Meet the editor

José Simão Antunes do Carmo obtained his master's degree in Hydraulics and Water Resources in 1990 from the University of Lisbon and his Ph.D. in Engineering Sciences in 1995 from the University of Coimbra, Portugal. He was director of several undergraduate and master's courses in Civil Engineering and Environmental Engineering in the period 1995-2010. He was a scientific advisor of twenty-five master's dissertations and two

Ph.D. theses in Hydraulics and Water Resources. He has published two books, sixty-five papers in scientific journals, fifteen book chapters, and more than one hundred papers in international conferences. He has edited eleven books and a special issue of a scientific journal. He is a member of the editorial board of several international journals. His main areas of scientific research are hydrodynamics, morphodynamics, coastal management, river and coastal processes, climate change, natural hazards, risks, and vulnerabilities.

## Contents


**6. Conclusions**

Electrification of agriculture is one of the main drivers for improving agricultural production and income of local farmers. Such investments have very low payback periods for the developing world and also present multiple site-benefits, such as reduced immigration to the big cities and abroad, creation of new jobs, increase of income, improvement of living conditions, and, ultimately, poverty alleviation.

The electrification of households is a challenging investment, as can be seen in Section 3.1. This is why the electrification of productive uses of energy has been proposed throughout the last decade in order to make both the electrification investments viable and improve the socio-economic conditions of these areas. Even with new digital technologies and business models developed in the last few years, it is very difficult to deploy viable microgrid investments through only commercial lending.

With the aid of digital technologies, it is easy to understand that the profits presented by agricultural electrification are so high, they can actually cross-subsidize household electrification. If the agricultural cooperatives and businesses becomes the main investor in a household electrification activity and this is considered a part of an agricultural electrification investment, it is possible to see higher electrification rates in the short term. This approach is fully in line with the guidelines for institutional and policy frameworks for microgrids that have been adopted by the African Union Commission and are also fully in line with the policy and regulatory frameworks of many Sub-Saharan African countries.

This paper provides justification for why such business models need to be developed further, applied, pilot tested, and evaluated in Sub-Saharan Africa.

**Author Contributions:** Conceptualization, G.K.; methodology, G.K. and A.T.B.; software, G.K.; validation, G.K. and D.B.; investigation, G.K.; resources, G.K. and A.T.B.; data curation, G.K. and D.B.; writing—original draft preparation, G.K.; writing—review and editing, D.B. and A.T.B.; visualization, G.K. and A.B.; supervision, D.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.


**•** Tuning frequency planar radiators,

**•** Dual frequency transmitters,

**•** Multilayer structures.

**2. Analyzed antenna**

planar array applications [2].

Choice of laminates and other materials for the implementation of the antenna and antenna system is one of the most important steps in the process of designing microstrip antennas. Planar microstrip antenna can be built with the theoretically infinite number of layers. This solution, unfortunately, leads to a reduction in antenna efficiency and leads to excitation of surface waves. In order to provide the required bandwidth efficiency of the antenna work and we need to limit the number of layers to this, to obtain both wide bandwidth operation and high efficiency.

In this case the optimization is folded, since all possible combinations of parameters will be examined. This optimization is time-consuming and complex process. In Figure 2 an algorithm of the optimization was presented. Bandwidth planar antenna can be expressed using the equation (1):

$$B = \frac{VSWR - 1}{\frac{c\sqrt{\varepsilon\_e}}{4f\_0h}}\tag{1}$$

and permittivity (Figure 3). On each of graphs optimum areas marked on the color red. Layer

Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna

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37

The object of the study is primarily broadband properties of the antenna input impedance and directional properties, which determine the further use of the model. Particular attention is

h3 has the optimum area smallest of all examined layers.

**5. The results of the optimization process**

**Figure 2.** Algorithm of the optimization

where:

*Q* - quality factor

*f* 0 - center frequency of band

*εe* - permittivity

*h* - thickness of antenna

Optimization parameters:

In order to optimize the iterative method was used. It is time consuming but allowed us to investigate the effect of dielectric parameters of the antenna operating band (fig.3). In the optimization process the following steps of changes of input parameters were accepted:

#### **4. Limitations of the optimization**

Permeability and thickness of each layer are limited typical values offered by various manu‐ facturers such as ROGERS, ARLON, etc. Different companies offer dielectrics with very similar structural parameters. Therefore, the values of h and εr values are limited discrete values occurring in the family.

As a result of computational series this way conducted for every of layers three-dimensional graphs giving the full image and the inspection of all possible combinations to the thickness Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna http://dx.doi.org/10.5772/54661 37

**Figure 2.** Algorithm of the optimization

we need to limit the number of layers to this, to obtain both wide bandwidth operation and

In this case the optimization is folded, since all possible combinations of parameters will be examined. This optimization is time-consuming and complex process. In Figure 2 an algorithm of the optimization was presented. Bandwidth planar antenna can be expressed using the

0

In order to optimize the iterative method was used. It is time consuming but allowed us to investigate the effect of dielectric parameters of the antenna operating band (fig.3). In the optimization process the following steps of changes of input parameters were accepted:

Permeability and thickness of each layer are limited typical values offered by various manu‐ facturers such as ROGERS, ARLON, etc. Different companies offer dielectrics with very similar structural parameters. Therefore, the values of h and εr values are limited discrete values

As a result of computational series this way conducted for every of layers three-dimensional graphs giving the full image and the inspection of all possible combinations to the thickness

4 *e*

*VSWR B c f h* e

1

(1)

high efficiency.

36 Advancement in Microstrip Antennas with Recent Applications

equation (1):

where:

*Q* - quality factor

*εe* - permittivity

*f* 0 - center frequency of band

*h* - thickness of antenna

Optimization parameters:

**•** Layers permittivity: ε1, ε2, ε3, ε4

**•** Layers thickness: h1, h2, h3, h4 (Fig.1)

**•** electric penetrability of layers (*ε*1, *ε*2, *ε*3, *ε*4) – 0.05

**•** thickness of layers (h1, h2, h3, h4) – 0.05 [mm]

**4. Limitations of the optimization**

occurring in the family.

and permittivity (Figure 3). On each of graphs optimum areas marked on the color red. Layer h3 has the optimum area smallest of all examined layers.

#### **5. The results of the optimization process**

The object of the study is primarily broadband properties of the antenna input impedance and directional properties, which determine the further use of the model. Particular attention is paid to the bandwidth of the work, which was the basic parameter determining the final construction of the structure. Using the current state of knowledge should lead to the use of dielectrics with relatively lowest values of electrical permittivity. Optimization was carried out by examining the every of the layers in structure. The results to optimize were presented on the graphs below. The optimization process was as follows: for each layer has been studied sufficiently large set of combinations of thickness and permeability, and for each of them determined the bandwidth of operation. As a result of a series of calculations for each of the layers was formed three-dimensional graphs which give a complete picture and review all possible combinations of thickness and permeability. On each of the graphs obtained areas with the best bandwidth - in the diagrams shown in red. As can be seen in the following analysis for each layer there is at least some optimum combinations. A limitation of choosing the right laminate is the availability of mass-produced laminates of sufficient thickness and permeabil‐ ity. Laminates as well as other electronic components such as resistors and capacitors are produced in the so-called series with typical values, with defined thicknesses and permittivity. This is some major difficulty for designers. The process of optimization and testing of all parameters of the antenna was carried out using IE3D software (Zeland Software) based on the method of moments. In order to verify the correctness of their analysis before the construction of physical model of antenna we one more time made calculations the VSWR and radiation characteristics of the final model using a different calculation method (fig.10 and 11). To perform calculations in order to verify the selected software CST Microwave Studio based on FDTD method. Smith chart of wideband multilayer antenna is show in figure 9.

Figure 9. Smith chart of wideband multilayer antenna. **Figure 3.** Results of optimization for the parameters of the four layers of the aperture-coupled microstrip antenna

that despite these changes the antenna VSWR <2.

Figure 10.Figure 10. Verification of model with using CST.

Input impedance of the antenna in operating band varies in the range of 30 to 70 [Ω]. This input impedance makes full use of the antenna in the whole operating band. Such changes in the impedance is a side effect for maximum bandwidth . It should be noted

The results also show how little room for maneuver there is for choosing the right laminate structure. For some structures may unfortunately find that the physical realization is impos‐ sible because in our area of interest is not in any laminate. Then we would look for a solution by changing the dimensions of the radiating elements so as to be able to use existing laminates.

Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna

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The thickness of layers in a multilayer structure is one of the more important elements affecting directly on the bandwidth of the work the whole structure of radiation. Analysis the impact of the thickness the layers on the bandwidth in the structure consisted of the cyclic change in thickness (in steps of 0.05 mm) layer and setting the bandwidth (VSWR <2) when the other elements in the construction of the antenna in the same state. Maintaining other elements of the antenna can be sure that the effect is obtained only from changes in thickness. The analysis was performed for all layers occurring in the structure. For obtained in the optimization

The first was analyzed h4 layer. It is located at the top of the antenna. The results are illustrated in Figure 4. The results can be concluded that the bandwidth of the work at a level above 50% can be achieved by changes in the thickness of this layer in the range from 0.008 to 0.062λ0.

As a result of optimization selected the following dielectrics:

**6. Influence of dielectric parameters on antenna bandwidth**

process the parameters of laminates determined parameters of the antenna.

h1=1,57 mm, ε1 =2.2 - Rogers-RT/duroid 5880

h4 =0,25mm, ε4 =3.50 - Rogers/RO3035

**Figure 4.** Influence thickness of h4 layer on bandwidth

h2 =3,048 mm, ε2 =2.6 -Rogers-RT/ULTRALAM 2000 h3 =3 mm, ε3 =1.07- polymethacrylamid hard foam.

The radiation pattern of antenna has stable shape in the whole operating band. In the whole frequency range the gain of antenna

(calculated) is around 5 [dBi]. The width of the radiation characteristics (- 3dB) is around 100 °.

The results also show how little room for maneuver there is for choosing the right laminate structure. For some structures may unfortunately find that the physical realization is impos‐ sible because in our area of interest is not in any laminate. Then we would look for a solution by changing the dimensions of the radiating elements so as to be able to use existing laminates.

As a result of optimization selected the following dielectrics:

The process of optimization and testing of all parameters of the antenna was carried out using IE3D software (Zeland Software) h1=1,57 mm, ε1 =2.2 - Rogers-RT/duroid 5880 h2 =3,048 mm, ε2 =2.6 -Rogers-RT/ULTRALAM 2000 h3 =3 mm, ε3 =1.07- polymethacrylamid hard foam. h4 =0,25mm, ε4 =3.50 - Rogers/RO3035

paid to the bandwidth of the work, which was the basic parameter determining the final construction of the structure. Using the current state of knowledge should lead to the use of dielectrics with relatively lowest values of electrical permittivity. Optimization was carried out by examining the every of the layers in structure. The results to optimize were presented on the graphs below. The optimization process was as follows: for each layer has been studied sufficiently large set of combinations of thickness and permeability, and for each of them determined the bandwidth of operation. As a result of a series of calculations for each of the layers was formed three-dimensional graphs which give a complete picture and review all possible combinations of thickness and permeability. On each of the graphs obtained areas with the best bandwidth - in the diagrams shown in red. As can be seen in the following analysis for each layer there is at least some optimum combinations. A limitation of choosing the right laminate is the availability of mass-produced laminates of sufficient thickness and permeabil‐ ity. Laminates as well as other electronic components such as resistors and capacitors are produced in the so-called series with typical values, with defined thicknesses and permittivity.

FDTD method. Smith chart of wideband multilayer antenna is show in figure 9.

based on the method of moments. In order to verify the correctness of their analysis before the construction of physical model of

Input impedance of the antenna in operating band varies in the range of 30 to 70 [Ω]. This input impedance makes full use of the antenna in the whole operating band. Such changes in the impedance is a side effect for maximum bandwidth . It should be noted

The radiation pattern of antenna has stable shape in the whole operating band. In the whole frequency range the gain of antenna

(calculated) is around 5 [dBi]. The width of the radiation characteristics (- 3dB) is around 100 °.

This is some major difficulty for designers.

38 Advancement in Microstrip Antennas with Recent Applications

Figure 9. Smith chart of wideband multilayer antenna.

**Figure 3.** Results of optimization for the parameters of the four layers of the aperture-coupled microstrip antenna

that despite these changes the antenna VSWR <2.

Figure 10.Figure 10. Verification of model with using CST.

#### antenna we one more time made calculations the VSWR and radiation characteristics of the final model using a different calculation method (fig.10 and 11). To perform calculations in order to verify the selected software CST Microwave Studio based on **6. Influence of dielectric parameters on antenna bandwidth**

The thickness of layers in a multilayer structure is one of the more important elements affecting directly on the bandwidth of the work the whole structure of radiation. Analysis the impact of the thickness the layers on the bandwidth in the structure consisted of the cyclic change in thickness (in steps of 0.05 mm) layer and setting the bandwidth (VSWR <2) when the other elements in the construction of the antenna in the same state. Maintaining other elements of the antenna can be sure that the effect is obtained only from changes in thickness. The analysis was performed for all layers occurring in the structure. For obtained in the optimization process the parameters of laminates determined parameters of the antenna.

**Figure 4.** Influence thickness of h4 layer on bandwidth

The first was analyzed h4 layer. It is located at the top of the antenna. The results are illustrated in Figure 4. The results can be concluded that the bandwidth of the work at a level above 50% can be achieved by changes in the thickness of this layer in the range from 0.008 to 0.062λ0. Figure 4. Influence thickness of h4 layer on bandwidth

area of the upper frequencies.

0.250 (fig.6)

When we increase the thickness of the layer above the limit then the range bandwidth is narrows in the area of the upper frequencies. The first was analyzed h4 layer. It is located at the top of the antenna. The results are illustrated in Figure 4. The results can be concluded that the bandwidth of the work at a level above 50% can be achieved by changes in the thickness of this layer in the range from 0.008 to 0.0620. When we increase the thickness of the layer above the limit then the range bandwidth is narrows in the

Figure 5. VSWR for values outside of the optimal range (a) thickness >0.0620 (b) thickness <0.0080 **Figure 5.** VSWR for values outside of the optimal range (a) thickness >0.062λ0 (b) thickness <0.008λ0

Using the same calculation process, we determined the influence of thickness h3 to h1 on the bandwidth of the antenna. **7. Study the impact of the total thickness of the antenna operating bandwidth** Using the same calculation process, we determined the influence of thickness h3 to h1 on the bandwidth of the antenna.

Using the results obtained during the optimization and additional numerical calculations can be concluded that the multilayer

**Figure 6.** Bandwidth as a function of thickness of the multilayer structure due to the change in thickness of each layer.

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For optimized model antenna the electrical parameters were determined: VSWR, impedance, characteristic of radiation. Figure 6 shows the VSWR of optimal single patch antenna. How‐ ever, the input impedance is shown in Figures 7 (reactance and resistance). Resistance in the range of work fluctuates around the value of 50Ω. the reactance value fluctuates around the

**8. Calculation of parameters for optimum model**

value of the 0.

**Figure 7.** VSWR of optimal single patch antenna.

#### structure achieves the highest bandwidth for the measured quantity of work, as the ratio of thickness of the antenna to the wavelength and containing in the range of 0.21-0.27 0. When the thickness of the structure has a value outside this range is rapidly declining bandwidth operation. For all layers of optimum thickness ratio of the total structure to the radiated wave length (center frequency 8.27 GHz antenna operation) at which it achieves the greatest band of operation is in all cases very close to the value of **7. Study the impact of the total thickness of the antenna operating bandwidth**

Mistake how we can make when selecting layer h1 and h2 is the smallest of all the layers, both in terms of thickness and permeability. Minor deviations from the optimum value (due to the bandwidth of operation) the effect of limiting the bandwidth of operation well below 50%. For working bandwidth> 50% of the thickness and permittivity of each layer should contain, respectively, in the intervals: - layer h1: thickness from 0.041 to 0.062 0 and permittivity εr1 from 1.78 to 2.62; - layer h2: thickness from 0.084 to 0.121 0 and permittivity εr2 from 2.28 to 2.77; Using the results obtained during the optimization and additional numerical calculations can be concluded that the multilayer structure achieves the highest bandwidth for the measured quantity of work, as the ratio of thickness of the antenna to the wavelength and containing in the range of 0.21-0.27 λ0. When the thickness of the structure has a value outside this range is rapidly declining bandwidth operation. For all layers of optimum thickness ratio of the total structure to the radiated wave length (center frequency 8.27 GHz antenna operation) at which it achieves the greatest band of operation is in all cases very close to the value of 0.25λ0 (fig.6)

**Figure 6.** Bandwidth as a function of thickness of the multilayer structure due to the change in thickness of each layer.

#### **8. Calculation of parameters for optimum model**

When we increase the thickness of the layer above the limit then the range bandwidth is

Using the same calculation process, we determined the influence of thickness h3 to h1 on the bandwidth of the antenna.

Using the same calculation process, we determined the influence of thickness h3 to h1 on the

Using the results obtained during the optimization and additional numerical calculations can be concluded that the multilayer structure achieves the highest bandwidth for the measured quantity of work, as the ratio of thickness of the antenna to the wavelength and containing in the range of 0.21-0.27 0. When the thickness of the structure has a value outside this range is rapidly declining bandwidth operation. For all layers of optimum thickness ratio of the total structure to the radiated wave length (center frequency 8.27 GHz antenna operation) at which it achieves the greatest band of operation is in all cases very close to the value of

Mistake how we can make when selecting layer h1 and h2 is the smallest of all the layers, both in terms of thickness and permeability. Minor deviations from the optimum value (due to the bandwidth of operation) the effect of limiting the bandwidth of operation well below 50%. For working bandwidth> 50% of the thickness and permittivity of each layer should contain,

Using the results obtained during the optimization and additional numerical calculations can be concluded that the multilayer structure achieves the highest bandwidth for the measured quantity of work, as the ratio of thickness of the antenna to the wavelength and containing in the range of 0.21-0.27 λ0. When the thickness of the structure has a value outside this range is rapidly declining bandwidth operation. For all layers of optimum thickness ratio of the total structure to the radiated wave length (center frequency 8.27 GHz antenna operation) at which it achieves the greatest band of operation is in all cases very close to the value of 0.25λ0 (fig.6)

Mistake how we can make when selecting layer h1 and h2 is the smallest of all the layers, both in terms of thickness and permeability. Minor deviations from the optimum value (due to the bandwidth of operation) the effect of limiting the bandwidth of operation well below 50%. For working bandwidth> 50% of the thickness and permittivity of each layer should contain,

**•** layer h1: thickness from 0.041 to 0.062 λ0 and permittivity εr1 from 1.78 to 2.62;

**•** layer h2: thickness from 0.084 to 0.121 λ0 and permittivity εr2 from 2.28 to 2.77;

**•** layer h4: thickness from 0.008 to 0.062 λ0 and permittivity εr4 from 2.05 to 4.62;

**•** layer h3: thickness from 0.077 to 0.176 λ0 and permittivity εr3 from 1 to 1.36;

**7. Study the impact of the total thickness of the antenna operating bandwidth**

**7. Study the impact of the total thickness of the antenna operating**

**Figure 5.** VSWR for values outside of the optimal range (a) thickness >0.062λ0 (b) thickness <0.008λ0

The first was analyzed h4 layer. It is located at the top of the antenna. The results are illustrated in Figure 4. The results can be concluded that the bandwidth of the work at a level above 50% can be achieved by changes in the thickness of this layer in the range from 0.008 to 0.0620. When we increase the thickness of the layer above the limit then the range bandwidth is narrows in the

narrows in the area of the upper frequencies.

40 Advancement in Microstrip Antennas with Recent Applications

Figure 5. VSWR for values outside of the optimal range (a) thickness >0.0620 (b) thickness <0.0080

Figure 4. Influence thickness of h4 layer on bandwidth

area of the upper frequencies.

0.250 (fig.6)

**bandwidth**

respectively, in the intervals:

respectively, in the intervals:

bandwidth of the antenna.

For optimized model antenna the electrical parameters were determined: VSWR, impedance, characteristic of radiation. Figure 6 shows the VSWR of optimal single patch antenna. How‐ ever, the input impedance is shown in Figures 7 (reactance and resistance). Resistance in the range of work fluctuates around the value of 50Ω. the reactance value fluctuates around the value of the 0.

**Figure 7.** VSWR of optimal single patch antenna.

**Figure 8.** Reactance and resistance of optimal single patch antenna.

The resultant input impedance allows the full use of the antenna in the whole range of work. As a result of optimizing the working range was achieved 62.5% (VSWR<2).

**Figure 9.** Smith chart of wideband multilayer antenna.

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**Figure 10.** Figure 10. Verification of model with using CST.

The process of optimization and testing of all parameters of the antenna was carried out using IE3D software (Zeland Software) based on the method of moments. In order to verify the correctness of their analysis before the construction of physical model of antenna we one more time made calculations the VSWR and radiation characteristics of the final model using a different calculation method (fig.10 and 11). To perform calculations in order to verify the selected software CST Microwave Studio based on FDTD method. Smith chart of wideband multilayer antenna is show in figure 9.

Input impedance of the antenna in operating band varies in the range of 30 to 70 [Ω]. This input impedance makes full use of the antenna in the whole operating band. Such changes in the impedance is a side effect for maximum bandwidth. It should be noted that despite these changes the antenna VSWR <2.

The radiation pattern of antenna has stable shape in the whole operating band. In the whole frequency range the gain of antenna (calculated) is around 5 [dBi]. The width of the radiation characteristics (- 3dB) is around 100 °.

Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna http://dx.doi.org/10.5772/54661 43

**Figure 9.** Smith chart of wideband multilayer antenna.

**Figure 8.** Reactance and resistance of optimal single patch antenna.

42 Advancement in Microstrip Antennas with Recent Applications

multilayer antenna is show in figure 9.

changes the antenna VSWR <2.

characteristics (- 3dB) is around 100 °.

The resultant input impedance allows the full use of the antenna in the whole range of work.

The process of optimization and testing of all parameters of the antenna was carried out using IE3D software (Zeland Software) based on the method of moments. In order to verify the correctness of their analysis before the construction of physical model of antenna we one more time made calculations the VSWR and radiation characteristics of the final model using a different calculation method (fig.10 and 11). To perform calculations in order to verify the selected software CST Microwave Studio based on FDTD method. Smith chart of wideband

Input impedance of the antenna in operating band varies in the range of 30 to 70 [Ω]. This input impedance makes full use of the antenna in the whole operating band. Such changes in the impedance is a side effect for maximum bandwidth. It should be noted that despite these

The radiation pattern of antenna has stable shape in the whole operating band. In the whole frequency range the gain of antenna (calculated) is around 5 [dBi]. The width of the radiation

As a result of optimizing the working range was achieved 62.5% (VSWR<2).

**Figure 10.** Figure 10. Verification of model with using CST.

Figure 11.Radiations pattern of multilayer antenna-simulations **Figure 11.** Radiations pattern of multilayer antenna-simulations

Selection of components of the antenna (thickness and permeability layers) gives the value of VSWR<2. The antenna's radiating patch has very similar level and distribution of currents. The main radiating element is side edges of the patches are the same as in single-layer structures. The distribution of currents guarantees consistent with the direction of the feed line. Selection of components of the antenna (thickness and permeability layers) gives the value of VSWR<2. The antenna's radiating patch has very similar level and distribution of currents. The main radiating element is side edges of the patches are the same as in single-layer structures. The distribution of currents guarantees consistent with the direction of the feed line.

Figure 12.Current distribution in antanna elements

**9. Physical model of the antenna**

**Figure 12.** Current distribution in antanna elements

Figure 13.Layers of antenna and model of antenna.

**Figure 13.** Layers of antenna and model of antenna.

Figure 14.Dimension of h1 layer

by the h1 and ε1.

impedance are a side effect for a maximum bandwidth of work.

changes of parameters of the aerial in (checked in measurements).

aerial in.

In the figure 13 shows the antenna layers. First from left is put layer h1 with coupling slot. Holes in layers of the antenna were carried out intentionally with a view to precise connecting with oneself layers, they aren't bringing changes of parameters of the

Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna

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In Figure 13 a ready model of the aerial was described, the structure of aerials is coated with foamed PCV. They aren't bringing

Obtained in a multi-layer band work is not possible in single layer antennas [2]. In the whole range of work input impedance of the antenna is stable. Antenna input impedance in the band of work is changing in the range of 36 to 67 []. Such changes in the

The result for the physical model confirms the correctness of the analysis and calculations obtained using the calculation method based on the method of moments. Three of the four laminates used in its construction include teflon, and one of the layers is made of polimethacrylamid foam. This caused some difficulties in the technological process of joining them together and generates small

The resulting optimization model of the antenna is shown in Figures 9, 10 and 11. The antenna is a multi-layered structure having in its construction of two radiating elements in the form of "patches" located on successive layers of the dish. Patch located in the h2 layer is fed by a line through a gap made in the plane of the masses. Above it there is another patch that by using the resonance (of another already in the structure) greatly improves the bandwidth of operation. The power supply line located on the layer defined

inaccuracies in the contact of subsequent layers. This gave slight differences between calculations and measurements.

#### **9. Physical model of the antenna**

In the figure 13 shows the antenna layers. First from left is put layer h1 with coupling slot. Holes in layers of the antenna were carried out intentionally with a view to precise connecting with oneself layers, they aren't bringing changes of parameters of the aerial in.

In Figure 13 a ready model of the aerial was described, the structure of aerials is coated with foamed PCV. They aren't bringing changes of parameters of the aerial in (checked in measurements).

In Figure 13 a ready model of the aerial was described, the structure of aerials is coated with foamed PCV. They aren't bringing **Figure 12.** Current distribution in antanna elements

changes of parameters of the aerial in (checked in measurements).

Figure 11.Radiations pattern of multilayer antenna-simulations

**Figure 11.** Radiations pattern of multilayer antenna-simulations

44 Advancement in Microstrip Antennas with Recent Applications

**9. Physical model of the antenna**

measurements).

[dBi]

Selection of components of the antenna (thickness and permeability layers) gives the value of VSWR<2. The antenna's radiating patch has very similar level and distribution of currents. The main radiating element is side edges of the patches are the same as in

[dBi] [dBi]

single-layer structures. The distribution of currents guarantees consistent with the direction of the feed line.

Selection of components of the antenna (thickness and permeability layers) gives the value of VSWR<2. The antenna's radiating patch has very similar level and distribution of currents. The main radiating element is side edges of the patches are the same as in single-layer structures.

In the figure 13 shows the antenna layers. First from left is put layer h1 with coupling slot. Holes in layers of the antenna were carried out intentionally with a view to precise connecting

In Figure 13 a ready model of the aerial was described, the structure of aerials is coated with foamed PCV. They aren't bringing changes of parameters of the aerial in (checked in

The distribution of currents guarantees consistent with the direction of the feed line.

with oneself layers, they aren't bringing changes of parameters of the aerial in.

Obtained in a multi-layer band work is not possible in single layer antennas [2]. In the whole range of work input impedance of the antenna is stable. Antenna input impedance in the band of work is changing in the range of 36 to 67 []. Such changes in the

The result for the physical model confirms the correctness of the analysis and calculations obtained using the calculation method based on the method of moments. Three of the four laminates used in its construction include teflon, and one of the layers is made of polimethacrylamid foam. This caused some difficulties in the technological process of joining them together and generates small

The resulting optimization model of the antenna is shown in Figures 9, 10 and 11. The antenna is a multi-layered structure having in its construction of two radiating elements in the form of "patches" located on successive layers of the dish. Patch located in the h2 layer is fed by a line through a gap made in the plane of the masses. Above it there is another patch that by using the resonance (of another already in the structure) greatly improves the bandwidth of operation. The power supply line located on the layer defined

inaccuracies in the contact of subsequent layers. This gave slight differences between calculations and measurements.

Figure 13.Layers of antenna and model of antenna. **Figure 13.** Layers of antenna and model of antenna.

Figure 14.Dimension of h1 layer

by the h1 and ε1.

impedance are a side effect for a maximum bandwidth of work.

Obtained in a multi-layer band work is not possible in single layer antennas [2]. In the whole range of work input impedance of the antenna is stable. Antenna input impedance in the band of work is changing in the range of 36 to 67 [Ω]. Such changes in the impedance are a side effect for a maximum bandwidth of work.

The result for the physical model confirms the correctness of the analysis and calculations obtained using the calculation method based on the method of moments. Three of the four laminates used in its construction include teflon, and one of the layers is made of polimetha‐ crylamid foam. This caused some difficulties in the technological process of joining them together and generates small inaccuracies in the contact of subsequent layers. This gave slight differences between calculations and measurements.

**Figure 15.** Dimension of h2 and h4 layers

**10. Result of measurements**

**•** Standing wave ratio VSWR

**•** Input impedance Z

**•** Radiation patterns

articles[12,13,14].

**•** Resistance R

**•** Reactance X

measured results in the frequency range (5,5-11,5 GHz) for :

h3 and h4.

The h2 layer is made of foam, which cannot be applied metallization. Therefore, the patch was placed on the bottom layer of h4. In result the radiating patch will be located between the layers

Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna

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47

Measurement of parameters and antenna characteristics were carried out at the Laboratory for Electromagnetic Compatibility of the Electronics Department of the Military Technical Academy equipped with an anechoic chamber. A prototype is made and the following

Figure 16 shows the model of antenna VSWR during measurements. In the next Figure 17 shows the results of measurements of VSWR, which reaches a value of less than 2 in frequency range from 5.8 GHz to 10.15 GHz. during the measurement parameters and antenna charac‐ teristics of dielectric parameters was also studied based on the methodology described in the

**Figure 14.** Dimension of h1 layer

The resulting optimization model of the antenna is shown in Figures 9, 10 and 11. The antenna is a multi-layered structure having in its construction of two radiating elements in the form of "patches" located on successive layers of the dish. Patch located in the h2 layer is fed by a line through a gap made in the plane of the masses. Above it there is another patch that by using the resonance (of another already in the structure) greatly improves the bandwidth of operation. The power supply line located on the layer defined by the h1 and ε1.

**Figure 15.** Dimension of h2 and h4 layers

Obtained in a multi-layer band work is not possible in single layer antennas [2]. In the whole range of work input impedance of the antenna is stable. Antenna input impedance in the band of work is changing in the range of 36 to 67 [Ω]. Such changes in the impedance are a side effect

The result for the physical model confirms the correctness of the analysis and calculations obtained using the calculation method based on the method of moments. Three of the four laminates used in its construction include teflon, and one of the layers is made of polimetha‐ crylamid foam. This caused some difficulties in the technological process of joining them together and generates small inaccuracies in the contact of subsequent layers. This gave slight

The resulting optimization model of the antenna is shown in Figures 9, 10 and 11. The antenna is a multi-layered structure having in its construction of two radiating elements in the form of "patches" located on successive layers of the dish. Patch located in the h2 layer is fed by a line through a gap made in the plane of the masses. Above it there is another patch that by using the resonance (of another already in the structure) greatly improves the bandwidth of

operation. The power supply line located on the layer defined by the h1 and ε1.

for a maximum bandwidth of work.

46 Advancement in Microstrip Antennas with Recent Applications

**Figure 14.** Dimension of h1 layer

differences between calculations and measurements.

The h2 layer is made of foam, which cannot be applied metallization. Therefore, the patch was placed on the bottom layer of h4. In result the radiating patch will be located between the layers h3 and h4.

#### **10. Result of measurements**

Measurement of parameters and antenna characteristics were carried out at the Laboratory for Electromagnetic Compatibility of the Electronics Department of the Military Technical Academy equipped with an anechoic chamber. A prototype is made and the following measured results in the frequency range (5,5-11,5 GHz) for :

Figure 16 shows the model of antenna VSWR during measurements. In the next Figure 17 shows the results of measurements of VSWR, which reaches a value of less than 2 in frequency range from 5.8 GHz to 10.15 GHz. during the measurement parameters and antenna charac‐ teristics of dielectric parameters was also studied based on the methodology described in the articles[12,13,14].

**Figure 16.** Model of antenna during VSWR measurmeants.

**Figure 18.** Measured input impedance of optimal single patch antenna.

**Figure 19.** Photos of the antenna during measurments in the anechoic chamber.

Figure 18 shows the measured values of resistance and reactance of antenna model. The meas‐ ured resistance value ranges from 35 to 55 ohms. Reactance varies in the range from -10 to 5 ohms.

Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna

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49

**Figure 17.** Measured VSWR of optimal single patch.

Obtained in the measurement bandwidth of the work is:

$$B = \frac{2(f\_{\text{max}} - f\_{\text{min}})}{f\_{\text{max}} + f\_{\text{min}}} \cdot 100\% = \frac{2(10150 - 5800)}{(10150 + 5800)} \cdot 100\% = \frac{2 \cdot 4350}{15950} \cdot 100\% \approx 55\% \tag{2}$$

Figure 18 shows the measured values of resistance and reactance of antenna model.

**Figure 18.** Measured input impedance of optimal single patch antenna.

Figure 18 shows the measured values of resistance and reactance of antenna model. The meas‐ ured resistance value ranges from 35 to 55 ohms. Reactance varies in the range from -10 to 5 ohms.

**Figure 19.** Photos of the antenna during measurments in the anechoic chamber.

**Figure 17.** Measured VSWR of optimal single patch.

**Figure 16.** Model of antenna during VSWR measurmeants.

48 Advancement in Microstrip Antennas with Recent Applications

max min max min

*f f B f f*

Obtained in the measurement bandwidth of the work is:

2( ) 2(10150 5800) 2 4350 100% 100% 100% 55% ) (10150 5800) 15950

Figure 18 shows the measured values of resistance and reactance of antenna model.

The subject carried out by the author toprimarily study broadening the antenna bandwidth properties, which confirm the elimination of the problem of narrowband in the structures of planar antennas and directional properties. Particular attention is paid to the impedance properties defined by examining the standing wave ratio (VSWR) in the bandwidth of the antenna, the ratio was determined relative to a standard value of impedance 50Ώ. Radiation characteristics was investigated for frequencies from 5.5 GHz to 11.5 GHz in steps of 1 GHz. The paper presents the characteristics for a center frequency band operation (7.6 GHz) and for two frequencies distant by about 1 GHz bandwidth from the ends of the work, the frequency of 6.5 GHz and 9.5 GHz. For the same frequency were also determined and presented in the work sheet in the computer simulations. Figure 19.Photos of the antenna during measurments in the anechoic chamber. The subject carried out by the author toprimarily study broadening the antenna bandwidth properties, which confirm the elimination of the problem of narrowband in the structures of planar antennas and directional properties. Particular attention is paid to the impedance properties defined by examining the standing wave ratio (VSWR) in the bandwidth of the antenna, the ratio was determined relative to a standard value of impedance 50Ώ. Radiation characteristics was investigated for frequencies from 5.5 GHz to 11.5 GHz in steps of 1 GHz. The paper presents the characteristics for a center frequency band operation (7.6 GHz) and for

Figure 20 shows the far field radiation characteristics of the antenna at the center frequency (7.6 GHz) and at 6.5 and 9.5 GHz two frequencies distant by about 1 GHz bandwidth from the ends of the work, the frequency of 6.5 GHz and 9.5 GHz. For the same frequency were also determined and presented in the work sheet in the computer simulations.

Figure 20 shows the far field radiation characteristics of the antenna at the center frequency (7.6 GHz) and at 6.5 and 9.5 GHz

Width of the main lobe at the level of -3 [dB] in the whole operating band is approximately

Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna

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51

Width of the main lobe at the level of -3 [dB] in the whole operating band is approximately 140 °. Radiation pattern has a stable

Antenna gain is in the range from 4 dBi to 5.7 dBi. For multilayer structure with a bandwidth

Presented in a multi-layer structure despite the complex structure can be used to construct the antenna array, thereby increasing antenna gain. For this purpose, designed four element array,

Antenna gain is in the range from 4 dBi to 5.7 dBi. For multilayer structure with a bandwidth greater than 50% this is considered to

Presented in a multi-layer structure despite the complex structure can be used to construct the antenna array, thereby increasing

Parameters and characteristics of the antenna array were also measured in the anechoic chamber (fig.21). For the model was made the following we measured in this same frequency range (5,5-11,5 GHz) following parameters: standing wave ratio VSWR, input

impedance Z, resistance R, reactance X, radiation patterns. Measurement results are shown in Figures 23 and 24.

140 °. Radiation pattern has a stable shape in the frequency domain.

**Figure 21.** Measured antenna gain versus frequency.

shape in the frequency domain.

whose design is shown in Figure 21.

Figure 23.Antenna array during measurments in anechoic chamber.

be very good gain values.

Figure 22.Antenna array.

**Figure 22.** Antenna array.

Figure 21.Measured antenna gain versus frequency.

greater than 50% this is considered to be very good gain values.

antenna gain. For this purpose, designed four element array, whose design is shown in Figure 21.

Figure 20.Radiation paterrns(H - plane). **Figure 20.** Radiation paterrns(H - plane).

Width of the main lobe at the level of -3 [dB] in the whole operating band is approximately 140 °. Radiation pattern has a stable shape in the frequency domain.

**Figure 21.** Measured antenna gain versus frequency.

The subject carried out by the author toprimarily study broadening the antenna bandwidth properties, which confirm the elimination of the problem of narrowband in the structures of planar antennas and directional properties. Particular attention is paid to the impedance properties defined by examining the standing wave ratio (VSWR) in the bandwidth of the antenna, the ratio was determined relative to a standard value of impedance 50Ώ. Radiation characteristics was investigated for frequencies from 5.5 GHz to 11.5 GHz in steps of 1 GHz. The paper presents the characteristics for a center frequency band operation (7.6 GHz) and for two frequencies distant by about 1 GHz bandwidth from the ends of the work, the frequency of 6.5 GHz and 9.5 GHz. For the same frequency were also determined and presented in the

Figure 19.Photos of the antenna during measurments in the anechoic chamber.

Figure 20 shows the far field radiation characteristics of the antenna at the center frequency

5.8 GHz 6.5 GHz

7.6 GHz 9.6 GHz

frequency were also determined and presented in the work sheet in the computer simulations.

The subject carried out by the author toprimarily study broadening the antenna bandwidth properties, which confirm the elimination of the problem of narrowband in the structures of planar antennas and directional properties. Particular attention is paid to the impedance properties defined by examining the standing wave ratio (VSWR) in the bandwidth of the antenna, the ratio was determined relative to a standard value of impedance 50Ώ. Radiation characteristics was investigated for frequencies from 5.5 GHz to 11.5 GHz in steps of 1 GHz. The paper presents the characteristics for a center frequency band operation (7.6 GHz) and for two frequencies distant by about 1 GHz bandwidth from the ends of the work, the frequency of 6.5 GHz and 9.5 GHz. For the same

Figure 20 shows the far field radiation characteristics of the antenna at the center frequency (7.6 GHz) and at 6.5 and 9.5 GHz

work sheet in the computer simulations.

50 Advancement in Microstrip Antennas with Recent Applications

Figure 20.Radiation paterrns(H - plane).

**Figure 20.** Radiation paterrns(H - plane).

(7.6 GHz) and at 6.5 and 9.5 GHz

Antenna gain is in the range from 4 dBi to 5.7 dBi. For multilayer structure with a bandwidth greater than 50% this is considered to be very good gain values. Figure 21.Measured antenna gain versus frequency.

Presented in a multi-layer structure despite the complex structure can be used to construct the antenna array, thereby increasing antenna gain. For this purpose, designed four element array, whose design is shown in Figure 21. Antenna gain is in the range from 4 dBi to 5.7 dBi. For multilayer structure with a bandwidth greater than 50% this is considered to be very good gain values. Presented in a multi-layer structure despite the complex structure can be used to construct the antenna array, thereby increasing

antenna gain. For this purpose, designed four element array, whose design is shown in Figure 21.

impedance Z, resistance R, reactance X, radiation patterns. Measurement results are shown in Figures 23 and 24.

Parameters and characteristics of the antenna array were also measured in the anechoic chamber (fig.21). For the model was made the following we measured in this same frequency range (5,5-11,5 GHz) following parameters: standing wave ratio VSWR, input

Figure 22.Antenna array. **Figure 22.** Antenna array.

Figure 23.Antenna array during measurments in anechoic chamber.

shape in the frequency domain.

Figure 21.Measured antenna gain versus frequency.

be very good gain values.

Parameters and characteristics of the antenna array were also measured in the anechoic cham‐ ber (fig.21). For the model was made the following we measured in this same frequency range (5,5-11,5 GHz) following parameters: standing wave ratio VSWR, input impedance Z, resist‐ ance R, reactance X, radiation patterns. Measurement results are shown in Figures 23 and 24. Figure 22.Antenna array. Parameters and characteristics of the antenna array were also measured in the anechoic chamber (fig.21). For the model was made

Width of the main lobe at the level of -3 [dB] in the whole operating band is approximately 140 °. Radiation pattern has a stable

Antenna gain is in the range from 4 dBi to 5.7 dBi. For multilayer structure with a bandwidth greater than 50% this is considered to

Presented in a multi-layer structure despite the complex structure can be used to construct the antenna array, thereby increasing

the following we measured in this same frequency range (5,5-11,5 GHz) following parameters: standing wave ratio VSWR, input

Figure 24.Impedance of antenna array- measurmeants.

**[Ω]**

Figure 25.Radiation paterrns of array.

**Figure 26.** VSWR – simualtions and measurments.

**Figure 25.** Radiation paterrns of array.

well as the FDTD method.

**11. Comparison of simulations and measurements**

**11. Comparison of simulations and measurements**

10,5 GHz 5,8 GHz

The most important parameter in view of the article is the course of VSWR as a function of frequency. The result obtained for the physical model confirms the correctness of the analysis and calculations obtained using the calculation method based on the method of moments, as

method of moments, as well as the FDTD method.

The most important parameter in view of the article is the course of VSWR as a function of frequency. The result obtained for the physical model confirms the correctness of the analysis and calculations obtained using the calculation method based on the

4 5 6 7 8 9 10 11 12 13 14

**Frequency [GHz]**

Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna

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53

impedance Z, resistance R, reactance X, radiation patterns. Measurement results are shown in Figures 23 and 24.

antenna gain. For this purpose, designed four element array, whose design is shown in Figure 21.

Figure 23.Antenna array during measurments in anechoic chamber.

**Figure 23.** Antenna array during measurments in anechoic chamber.

**Figure 24.** Impedance of antenna array- measurmeants.

**Frequency [GHz]** Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna http://dx.doi.org/10.5772/54661 53

4 5 6 7 8 9 10 11 12 13 14

Figure 25.Radiation paterrns of array. **Figure 25.** Radiation paterrns of array.

Parameters and characteristics of the antenna array were also measured in the anechoic cham‐ ber (fig.21). For the model was made the following we measured in this same frequency range (5,5-11,5 GHz) following parameters: standing wave ratio VSWR, input impedance Z, resist‐ ance R, reactance X, radiation patterns. Measurement results are shown in Figures 23 and 24.

Figure 23.Antenna array during measurments in anechoic chamber.

6,5 GHz

shape in the frequency domain.

Figure 21.Measured antenna gain versus frequency.

be very good gain values.

Figure 22.Antenna array.

52 Advancement in Microstrip Antennas with Recent Applications

**Figure 23.** Antenna array during measurments in anechoic chamber.

**Figure 24.** Impedance of antenna array- measurmeants.

Width of the main lobe at the level of -3 [dB] in the whole operating band is approximately 140 °. Radiation pattern has a stable

Antenna gain is in the range from 4 dBi to 5.7 dBi. For multilayer structure with a bandwidth greater than 50% this is considered to

Presented in a multi-layer structure despite the complex structure can be used to construct the antenna array, thereby increasing

antenna gain. For this purpose, designed four element array, whose design is shown in Figure 21.

#### The most important parameter in view of the article is the course of VSWR as a function of frequency. The result obtained for the **11. Comparison of simulations and measurements**

method of moments, as well as the FDTD method.

**11. Comparison of simulations and measurements**

Figure 24.Impedance of antenna array- measurmeants.

**[Ω]**

The most important parameter in view of the article is the course of VSWR as a function of frequency. The result obtained for the physical model confirms the correctness of the analysis and calculations obtained using the calculation method based on the method of moments, as well as the FDTD method.

physical model confirms the correctness of the analysis and calculations obtained using the calculation method based on the

Reduction of bandwidth in the upper-frequency of band (as confirmed by further simulations and calculations exploring the effects of precision interfaces between layers of the antenna on its parameters), the inaccuracy of the interfaces between layers of the dish. Three of the four laminates used in its construction include Teflon, and one of the layers is made of foam polimethacrylamid. This causes some technological difficulties in the process of connecting them together and produce a minimum of contact inaccuracy of subsequent layers. The simulations confirm the situation.

layer substrates and they parameters. Calculations show how difficult it is to choose optimal value for laminates when we want to obtain wide band. Permittivity and thickness are equally important for bandwidth antenna. The analysis of the antenna was done by the usage of IE3D - Zeland Software (method of moments - MoM). The method has been applied to the micro‐ strip-fed slot antenna and to the aperture coupled antenna with a good result when compared

Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna

http://dx.doi.org/10.5772/54661

55

The model of antenna allows use of all the positive properties of planar antennas with simultaneous work in a wide frequency range, which so far has been the main element to eliminate this type of the antenna of use in many designs. Given the trend for miniaturization of antenna devices and the development of radio technology and integrated systems presented in the paper of construction seems to be very prospective. The design of this antenna is a modern solution to the antenna, which is especially important in the use of the moving objects. The results of experimental studies measuring fully confirm the possibility of constructing planar antenna with wide bandwidth operation. In addition, ease of implementation of antenna arrays using planar antennas opens up new possibilities in the use of this construction. Designed antenna operates in X-band and certainly could be an interesting alternative to the

currently used antenna antennas operating in this band.

\*Address all correspondence to<EMAIL_ADDRESS>
Faculty of Electronics, Military University of Technology, Warsaw, Poland

[1] Turker, N, Gunes, F, & Yildirim, T. Artificial Neural Design of Microstrip Antennas",

[2] Kumar, G, & Ray, K. P. Broadband Microstrip Antennas" Artech House, (2003).

[3] Garg, R. pp. Bhartia, I. Bahl "Microstrip antenna design handbook" Artec Hause,

[4] Bi, Z, & Wu, K. Ch. Wu, J. Litva "And dispersive boundary condition handicap mi‐ crostrip component analysis using the FDTD method", IEEE Trans. Antennas and

and Marian Wnuk

Turk J Elec Engin, (2006). , 14(3)

Propagation, (1992). , 40, 774-777.

1-58053-244-6

INC

with measured data.

**Author details**

Marek Bugaj\*

**References**

**Figure 27.** Radiation paterrns of antenna measurments (a) and simualtions (b).

#### **12. Conclusion**

This article presents issues related to the theory and technique of multilayer planar antennas fed by the slot. This paper describes multilayer configuration to increase the BW of the antenna. This configuration has many advantages, including wide BW, reduction in spurious feed network radiation, and a symmetric radiation pattern with low cross-polarization. The antenna configuration with a resonant aperture yields wide BW by proper optimization of the coupling between the patch and the resonant slot. The basic characteristics and the effects of various parameters on the overall antenna performance are discussed.

The results of the study are satisfactory. The paper describes a clear advantage of multilayer antennas over monolayer ones, where the bandwidth is significantly narrower. The coupling aperture antenna after optimization can result in a considerable increase of bandwidth. The bandwidth of aerial is the outcome of the way feed as well as the utilization to build the multilayer substrates and they parameters. Calculations show how difficult it is to choose optimal value for laminates when we want to obtain wide band. Permittivity and thickness are equally important for bandwidth antenna. The analysis of the antenna was done by the usage of IE3D - Zeland Software (method of moments - MoM). The method has been applied to the micro‐ strip-fed slot antenna and to the aperture coupled antenna with a good result when compared with measured data.

The model of antenna allows use of all the positive properties of planar antennas with simultaneous work in a wide frequency range, which so far has been the main element to eliminate this type of the antenna of use in many designs. Given the trend for miniaturization of antenna devices and the development of radio technology and integrated systems presented in the paper of construction seems to be very prospective. The design of this antenna is a modern solution to the antenna, which is especially important in the use of the moving objects. The results of experimental studies measuring fully confirm the possibility of constructing planar antenna with wide bandwidth operation. In addition, ease of implementation of antenna arrays using planar antennas opens up new possibilities in the use of this construction. Designed antenna operates in X-band and certainly could be an interesting alternative to the currently used antenna antennas operating in this band.

#### **Author details**

Reduction of bandwidth in the upper-frequency of band (as confirmed by further simulations and calculations exploring the effects of precision interfaces between layers of the antenna on its parameters), the inaccuracy of the interfaces between layers of the dish. Three of the four laminates used in its construction include Teflon, and one of the layers is made of foam polimethacrylamid. This causes some technological difficulties in the process of connecting them together and produce a minimum of contact inaccuracy of subsequent layers. The

(a) (b)

This article presents issues related to the theory and technique of multilayer planar antennas fed by the slot. This paper describes multilayer configuration to increase the BW of the antenna. This configuration has many advantages, including wide BW, reduction in spurious feed network radiation, and a symmetric radiation pattern with low cross-polarization. The antenna configuration with a resonant aperture yields wide BW by proper optimization of the coupling between the patch and the resonant slot. The basic characteristics and the effects of various

The results of the study are satisfactory. The paper describes a clear advantage of multilayer antennas over monolayer ones, where the bandwidth is significantly narrower. The coupling aperture antenna after optimization can result in a considerable increase of bandwidth. The bandwidth of aerial is the outcome of the way feed as well as the utilization to build the multi-

**Figure 27.** Radiation paterrns of antenna measurments (a) and simualtions (b).

parameters on the overall antenna performance are discussed.

simulations confirm the situation.

54 Advancement in Microstrip Antennas with Recent Applications

**12. Conclusion**

Marek Bugaj\* and Marian Wnuk

\*Address all correspondence to<EMAIL_ADDRESS>
Faculty of Electronics, Military University of Technology, Warsaw, Poland

#### **References**

[5] Kin-Lu WongCompact and bradband miccrostrip antennas", (2002). by John Wiley & Sons, Inc., New York, 0-47122-111-2

**Chapter 3**

**Full-Wave Spectral Analysis of Resonant Characteristics**

During the last decades, superconducting antenna was one of the first microwave compo‐ nents tobedemonstratedas anapplicationofhigh-temperature superconductingmaterial[1-3]. High *Tc* superconducting microstrip antennas (HTSMA) are becoming popular and getting increased attention in both theoretical research and engineering applications due to their excellent advantages. Various patch configurations implemented on different types of substrates have been tested and investigated. In the design of microstrip antennas, anisotrop‐ ic substances have been increasingly popular. Especially the effects of uniaxial type anisotro‐ py have been investigated due to availability of this type of substances. These structures characterized by their low profile, small size, light weight, low cost and ease of fabrication, which makes them very suitable for microwave and millimeter-wave device applications [4-6]. HTSMA structures have shown significant superiority over corresponding devices fabricated with normal conductors such as gold, silver, or copper. Major property of superconductor is very low surface resistance; this property facilitates the development of microstrip antennas with better performance than conventional antennas. Compared to other patch geometries, the circular and annular ring microstrip patches printed on a uniaxial anisotropic substrate, have been more extensively studied for a long time by a number of investigators [7-11]. Circular microstrip patch can be used either as radiating antennas or as oscillators and filters in microwave integrated circuits (MIC's). The inherent advantage of an annular ring antenna is: first, the size of an annular ring for a given mode of operation is smaller than that of the circular disc resonating at the same frequency. Second, The presence of edges at the inner and outer radii causes more fringing than in the case of a circular microstrip antenna, in which fringing occurs only at the outer edge, and this implies more radiation from these edges, that leads to

> © 2013 Barkat; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2013 Barkat; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

distribution, and reproduction in any medium, provided the original work is properly cited.

**and Radiation Patterns of High Tc Superconducting**

**Circular and Annular Ring Microstrip Antennas**

Additional information is available at the end of the chapter

Ouarda Barkat

**1. Introduction**

http://dx.doi.org/10.5772/54665


**Abstract**

Advanced geopolymerization is a novel approach for the manufacture of geopolymers via innovative solid-state chemistry mechanism in which tailored geopolymeric precursors in solid powder form are the one part requirement, and only water is needed for its conversion to advanced geopolymeric material, in contrast to conventional process, where first solution of alkali is prepared and then mixed with silicoaluminous source materials. This novel process comprises of tailored geopolymeric precursors in solid powder form which is obtained via mechanochemical dry grinding of raw materials for prolonged hours. The basic raw materials include vitreous silica- and alumina-containing waste material/by-products, e.g. fly ash, activated by sodium hydroxide with or without sodium silicate. The solid powder needs only addition of water to form geopolymeric material. The advanced process includes solid-state reactions during dry grinding process and enables sequencing of reactions for preparation of geopolymeric material.

**Keywords:** advanced geopolymers, mechanochemical grinding, fly ash, mechanism, solid-state

### **1. Introduction**

Nowadays, safe disposal of different waste materials and industrial by-products is a key concern for global communities. In this context, the possibility to reuse industrial waste like fly ash to produce economical value-added important products, viz. geopolymers, by mitigating environmental hazards related to waste disposal is being explored on a large scale worldwide. The construction industries benefited using the concept of utilization of waste materials as resource material for the development of value-added materials certainly due to increasing cost and shortage of virgin raw materials. Reuse of industrial by-products to generate valueadded products is one of the promising ways to attain green and sustainable development. Geopolymers are one of the commercially important products suitable for construction sector manufactured using waste products like fly ash, slag, etc.

In this work a brief status of barriers in adopting conventional geopolymerization and the challenges that must be overcome to commercialize geopolymers is considered as research objective and successfully achieved by introducing advanced geopolymerization process for the manufacture of solid-state advanced geopolymeric materials. The authors of this research focused their aim to establish a new chemical mechanism behind advanced geopolymerization contrasting reaction mechanism of conventional geopolymerization with an objective to broaden application spectrum of geopolymer which will be an important part of sustainable development.


**3. Role of cytokines in oral cancer cell proliferation**

**Figure 3.** Schematic representation of coxsackievirus and adenovirus receptor on the tumor cells.

Finally, it was suggested that NCAM might be associated with not only a cell-to-cell adhesion mechanism but also tumorigenesis, including the occurrence, development, and perineural/

Further studies will be required to identify the signal transduction pathways by which treatment with cimetidine suppresses the growth of salivary gland tumors and to establish a strat-

Coxsackievirus and adenovirus receptor (CAR/CXADR), a transmembrane glycoprotein, was initially characterized as a viral attachment site on the surface of epithelial cells (**Figure 3**) [46]. Later it was identified as a component of the tight junction (TJ) complex, an interacting partner for a number of other TJ proteins and a regulator of TJ formation [47–52]. Furthermore, CAR is known to be a cell-cell adhesion molecule [53, 54]. In terms of function, loss of CAR has been considered to diminish intercellular adhesion, increase proliferation, and promote the migration as well as invasion of cancer cells [55, 56]. On the basis of these observations, a tumor-suppressive role of CAR in human cancers has speculated. Although it has recently been described [55–58] that CAR is observed in various organs, it is still unclear whether it is expressed in oral cancer. Therefore, we examined the role of CAR in SCC in the oral cavity (data not shown). This revealed that CAR was constitutively expressed in five oral SCC cell lines. To analyze the function of CAR, we then examined the proliferative activity of SAS cells

neural invasion of human salivary gland tumors.

88 Prevention, Detection and Management of Oral Cancer

egy for cimetidine-based therapy for those tumors.

**2.2. Coxsackievirus and adenovirus receptor (CAR/CXADR)**

Cytokines are composed of a large family of secreted proteins that bind to and signal through defined cell surface receptors on a wide variety of target cells, playing an important role in the maintenance of homeostasis. Furthermore, many cytokines share structural features and effects during inflammation, development, or immune responses.

The concept of a control mechanism for cellular growth via regulation of apoptosis has recently been erected in a wide variety of tissue systems. Changes in the balance between cell survival and death are definite signs of emergence of various tumors. Therefore, modulation of apoptosis is required so as to maintain the homeostasis of a living organism. The expression of cytokines and their receptors in human oral cancers has attracted a great deal of interest because of their potential importance in tumor immunity. In particular, it has been described that members of the tumor necrosis factor (TNF) family, including Fas/FasL and TNF-related apoptosis-inducing ligand (TRAIL), regulate the deletion of unnecessary immune cells through induction of apoptosis [59–61]. However, despite their expression of these obvious antigens, tumor evasion by the immune system is often inefficient. It is considered that tumor cells may also evade immune attack by expressing TRAIL, Fas ligand, or other molecules that induce apoptosis in activated T cells [62].

### **3.1. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)**

TRAIL, also called APO2 ligand (APO2L), is a novel member of the TNF cytokine family that was originally characterized by its ability to induce apoptosis [59, 60]. It is recognized that at least four closely related receptors bind to TRAIL: death receptor-4 (DR4) and DR5/ KILLER, which contain cytoplasmic death domains and signal apoptosis [60, 61]; decoy receptor-1 (DcR1) [61–63], which lacks a cytoplasmic tail and inhibits TRAIL function; and DcR2 [64, 65], which contains a cytoplasmic region with a truncated death domain that does not transduce the death signal [67]. TRAIL interacts with its agonistic receptors DR4 and DR5, inducing apoptosis in a wide variety of cancer cell lines derived from breast carcinoma, lung carcinoma, colon carcinoma, lymphoma, malignant melanoma, and malignant glioma [59, 60, 68, 69]. Although DR4 is expressed in many normal human tissues and cells, including spleen and peripheral blood leukocytes, TRAIL induces apoptosis in various cancer cells, but not in normal cells [70]. This may be explained by the fact that TRAIL also interacts with the antagonistic decoy receptors DcR1 and DcR2, which are expressed in normal tissues but not in cancer cells (**Figure 5**) [66, 67]. Neither DcR1 nor DcR2 receptors induce apoptosis, but they protect cells from TRAIL-induced apoptosis [64–66]. Until now, the biological involvement of the complex TRAIL receptor system has remained unclear, and the existing data are conflicting. Nevertheless, because of its selective cytotoxicity against tumor cells, TRAIL is regarded as a promising anticancer weapon that might be highly effective *in vivo* with few side effects, as it has little or no function on normal tissues.

samples (48%) of HOSCC tissue, and there was no correlation among the WHO grades. These findings suggest that HOSCC has the potential to escape immune surveillance by killing host T lymphocytes via DR4/TRAIL and DR5/TRAIL interactions, as suggested for FasL [72–74].

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**Figure 5.** Schematic representation of the death receptors and decoy receptors on the tumor cell.

The expression of decoy receptors in cancer cells is, however, a phenomenon that objects against previous reports [62, 63]. Indeed, several authors have currently described that a decoy receptor is expressed in various cancer types and our results are consistent with their findings [75–77]. Therefore, cancer cells may also avoid TRAIL-induced apoptosis by express-

On the other hand, cells differ significantly in their response to TRAIL. As contrasted to HUVEC or other oral cancer cells, only KB cells undergo significant apoptosis following exposure to recombinant human (rh)TRAIL. The reason why KB cells, despite their expression of

Commonly, the most proximal step in suppression of a death receptor pathway is inhibition of ligand binding. This may be acquired by lack, or the presence of decoy receptors [65–68], or mutations of death receptors [78, 79]. However, it has recently been described that there is no correlation between the expression of TRAIL receptor and susceptibility to TRAIL-induced apoptosis in various cancer types [75–77]. Furthermore, the existence of antiapoptotic proteins, such as bcl-2, bcl-xL, and/or fas-like IL-1-converting enzyme (FLICE)-like inhibitory protein [80, 81], also seems to be significant, as they are resistant to death receptor-mediated

ing a decoy receptor.

a decoy receptor, react to rhTRAIL remains unresolved.

TRAIL is expressed in most normal human cells and tissues, including the peripheral blood leukocytes, spleen, lung, and prostate, but not the brain [60]. However, the expression of TRAIL in human neoplasms is largely unknown. Accordingly, we have examined whether TRAIL and its receptors are expressed in HOSCC tissues or cell lines and whether these cell lines are sensitive to TRAIL-induced apoptosis [71]. This revealed that the mRNA and protein levels of TRAIL and its receptors are co-expressed in HOSCC cell lines in the absence of paracrine fratricide or autocrine suicide. Moreover, TRAIL protein was also detected in 24 of 50

**Figure 5.** Schematic representation of the death receptors and decoy receptors on the tumor cell.

the maintenance of homeostasis. Furthermore, many cytokines share structural features and

The concept of a control mechanism for cellular growth via regulation of apoptosis has recently been erected in a wide variety of tissue systems. Changes in the balance between cell survival and death are definite signs of emergence of various tumors. Therefore, modulation of apoptosis is required so as to maintain the homeostasis of a living organism. The expression of cytokines and their receptors in human oral cancers has attracted a great deal of interest because of their potential importance in tumor immunity. In particular, it has been described that members of the tumor necrosis factor (TNF) family, including Fas/FasL and TNF-related apoptosis-inducing ligand (TRAIL), regulate the deletion of unnecessary immune cells through induction of apoptosis [59–61]. However, despite their expression of these obvious antigens, tumor evasion by the immune system is often inefficient. It is considered that tumor cells may also evade immune attack by expressing TRAIL, Fas ligand, or other molecules that

TRAIL, also called APO2 ligand (APO2L), is a novel member of the TNF cytokine family that was originally characterized by its ability to induce apoptosis [59, 60]. It is recognized that at least four closely related receptors bind to TRAIL: death receptor-4 (DR4) and DR5/ KILLER, which contain cytoplasmic death domains and signal apoptosis [60, 61]; decoy receptor-1 (DcR1) [61–63], which lacks a cytoplasmic tail and inhibits TRAIL function; and DcR2 [64, 65], which contains a cytoplasmic region with a truncated death domain that does not transduce the death signal [67]. TRAIL interacts with its agonistic receptors DR4 and DR5, inducing apoptosis in a wide variety of cancer cell lines derived from breast carcinoma, lung carcinoma, colon carcinoma, lymphoma, malignant melanoma, and malignant glioma [59, 60, 68, 69]. Although DR4 is expressed in many normal human tissues and cells, including spleen and peripheral blood leukocytes, TRAIL induces apoptosis in various cancer cells, but not in normal cells [70]. This may be explained by the fact that TRAIL also interacts with the antagonistic decoy receptors DcR1 and DcR2, which are expressed in normal tissues but not in cancer cells (**Figure 5**) [66, 67]. Neither DcR1 nor DcR2 receptors induce apoptosis, but they protect cells from TRAIL-induced apoptosis [64–66]. Until now, the biological involvement of the complex TRAIL receptor system has remained unclear, and the existing data are conflicting. Nevertheless, because of its selective cytotoxicity against tumor cells, TRAIL is regarded as a promising anticancer weapon that might be highly effective *in vivo* with few side effects,

TRAIL is expressed in most normal human cells and tissues, including the peripheral blood leukocytes, spleen, lung, and prostate, but not the brain [60]. However, the expression of TRAIL in human neoplasms is largely unknown. Accordingly, we have examined whether TRAIL and its receptors are expressed in HOSCC tissues or cell lines and whether these cell lines are sensitive to TRAIL-induced apoptosis [71]. This revealed that the mRNA and protein levels of TRAIL and its receptors are co-expressed in HOSCC cell lines in the absence of paracrine fratricide or autocrine suicide. Moreover, TRAIL protein was also detected in 24 of 50

effects during inflammation, development, or immune responses.

**3.1. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)**

induce apoptosis in activated T cells [62].

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as it has little or no function on normal tissues.

samples (48%) of HOSCC tissue, and there was no correlation among the WHO grades. These findings suggest that HOSCC has the potential to escape immune surveillance by killing host T lymphocytes via DR4/TRAIL and DR5/TRAIL interactions, as suggested for FasL [72–74].

The expression of decoy receptors in cancer cells is, however, a phenomenon that objects against previous reports [62, 63]. Indeed, several authors have currently described that a decoy receptor is expressed in various cancer types and our results are consistent with their findings [75–77]. Therefore, cancer cells may also avoid TRAIL-induced apoptosis by expressing a decoy receptor.

On the other hand, cells differ significantly in their response to TRAIL. As contrasted to HUVEC or other oral cancer cells, only KB cells undergo significant apoptosis following exposure to recombinant human (rh)TRAIL. The reason why KB cells, despite their expression of a decoy receptor, react to rhTRAIL remains unresolved.

Commonly, the most proximal step in suppression of a death receptor pathway is inhibition of ligand binding. This may be acquired by lack, or the presence of decoy receptors [65–68], or mutations of death receptors [78, 79]. However, it has recently been described that there is no correlation between the expression of TRAIL receptor and susceptibility to TRAIL-induced apoptosis in various cancer types [75–77]. Furthermore, the existence of antiapoptotic proteins, such as bcl-2, bcl-xL, and/or fas-like IL-1-converting enzyme (FLICE)-like inhibitory protein [80, 81], also seems to be significant, as they are resistant to death receptor-mediated apoptosis. Holistically, our results also suggest that there may be no correlation between the expression of TRAIL receptor and sensitivity to TRAIL-induced apoptosis in HOSCC cell lines and that TRAIL-resistant cells (HSC-2, HSC-3, HSC-4, and Ca9-22) may express cytoprotective proteins that block TRAIL-induced apoptosis or that the apoptotic effect of TRAIL is regulated by other mechanisms. It has also been described that TRAIL, in combination with an anticancer drug, acts cooperatively to induce apoptosis in various cancer cells that are resistant to TRAIL or chemotherapy [75, 82, 83]. This combination of TRAIL with chemotherapeutic reagents might be a useful therapeutic strategy against TRAIL-resistant cell lines such as HSC-2, HSC-3, HSC-4, and Ca9-22 used in our investigation.

microRNA-mediated dysregulation) of MET [92–94]. c-Met overexpression and MET amplification are thought to be associated with a poorer prognosis in some types of tumors, including non-small cell lung cancer and gastric cancer [94]. In HOSCC, it has also been reported that c-Met expression is associated with cisplatin resistance and a strong propensity for metastasis *in vivo* [95], as well as a poor prognosis [96]. However, details of the involvement of c-Met in oral carcinogenesis are still unclear. Accordingly, we investigated how the relationship between the expression of c-Met and several tumor activation-related markers such as NF-κB is associated with oral carcinogenesis (data not shown). In addition, the expression and distribution of c-Met and NF-κB were also examined in HOSCC tissues (data not shown). The results of real-time qRT-PCR and immunoblot analysis indicated overexpression of c-Met mRNA and protein in SAS cells. Therefore, SAS cells were used in this study. To investigate how c-Met functions in SAS cells, c-Met knockdown analysis was performed. c-Met knockdown appeared to reduce the number of SAS cells. To confirm whether this had been due to apoptosis, caspase activity was then analyzed, and this revealed that apoptosis had indeed occurred via activation of caspases-9 and caspases-3/caspases-7 in SAS by c-Met knockdown. Furthermore, SAS showed cell cycle arrest at S/G2/M phase during this apoptotic cell death. Subsequently, to determine NF-κB expression after c-Met knockdown, we also used a siRNA approach to reduce the expression of c-Met and determine the effects on NF-κB activity. As expected, the level of c-Met mRNA was markedly reduced by c-Met siRNA. Moreover, c-Met knockdown by c-Met siRNA clearly decreased the activation of NF-κB mRNA in SAS cells, in comparison with controls. These data indicated that c-Met upregulated NF-κB activation and consequently that c-Met knockdown led to apoptosis of SAS cells. These combined data suggested that c-Met produced by autologous cancer cells promoted tumor growth. Furthermore, our *in vivo* studies demonstrated c-Metspecific immunoreactivity, consistent with the observation of NF-κB-positive cells in HOSCC biopsy samples (c-Met expression, 9/20 (45%); NF-κB expression, 18/20 cases (90%)). This result suggests that c-Met expression correlates with increased activation of NF-κB. Based on these in vitro and *in vivo* observations, it can be hypothesized that c-Met function leads to NF-κB activation and subsequently anti-apoptosis and that as a consequence, it may be associated

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with tumorigenesis, including growth, development, and angiogenesis in HOSCC.

**4. Energy metabolism in oral cancer**

**4.1. Glucose metabolism in oral cancer**

Further investigations of the role of c-Met will be required to fully understand c-Met-mediated tumor proliferation and to establish a therapeutic strategy for c-Met-based oral cancer.

In normal tissues, adenosine triphosphate (ATP) is mainly produced in mitochondria via complete oxidative phosphorylation (OXPHOS) of glucose. Conversely, only 10% of ATP is produced from glycolysis in which glucose is replaced to lactate [97]. Interestingly, cancer tissues possess high levels of glycolysis in the cytosol even under aerobic conditions, which is upregulated by PI3K/Akt signaling in the mitochondria, a phenomenon known as the "Warburg effect" or "aerobic glycolysis" [98–103]. More than 80 years ago, Otto Warburg

In fact, we are currently investigating the synergistic effects of α-mangostin and TRAIL on induction of apoptosis via the mitochondrial pathway in squamous cell carcinoma of the oral cavity [84]. To summarize, mangosteen (*Garcinia mangostana*) is a tree discovered in Southeast Asia, and the pericarp of its fruit has been used in folk medicine for the treatment of many human diseases. The rinds of mangosteen fruit contain a high concentration of xanthone, a type of polyphenol. One form of xanthone, α-mangostin, has been described to exhibit chemopreventive effects against chemically induced colon cancer through a decrease of c-Myc expression, suppressing tumor growth in a mouse model of mammary cancer. A recent study has proved the inhibitory effect of α-mangostin on the growth of prostate cancer. However, it is still unclear whether α-mangostin induces cell death in oral cancer. Then, the present study examined the impact of α-mangostin on HOSCC. First, we analyzed the expression of c-Myc in five HOSCC cell lines (HSC-2, HSC-3, HSC-4, Ca9-22, and SAS). The highest level of c-Myc mRNA expression was found in SAS cells and the lowest in HSC-4 cells. Therefore, SAS cells were treated with α-mangostin, which was observed to exert a weak cytocidal effect. Since α-mangostin has been described to exert synergistic effects on cancers when combined with anticancer drugs, we tried to evaluate these synergistic effects of α-mangostin in combination with TRAIL. We found that this combination induced apoptosis in SAS cells through the mitochondrial pathway via activation of caspase-3/caspase-7 and caspase-9, following the release of cytochrome c. In addition, this apoptosis was induced by S/G2/M-phase arrest. Immunoreactivity for c-Myc was revealed in the cytoplasm of cancer cells in 16 (40%) of the 40 cases of HOSCC. These data showed that the combination of α-mangostin and TRAIL may have considerable potential for the treatment of oral cancer.

Further investigation of TRAIL-mediated cell death, including the interaction of TRAIL and its receptors in oral cancer cells under various conditions, will be required to establish a strategy for TRAIL-based oral cancer therapy, which does not cause liver toxicity.

#### **3.2. Hepatocyte growth factor (HGF) and its receptor, c-Met**

The tyrosine kinase receptor c-Met ordinarily binds with hepatocyte growth factor (HGF), which triggers its involvement in processes such as cell differentiation, cell growth, angiogenesis, and embryogenesis [85, 86]. However, c-Met activation is also associated with processes related to malignant transformation, such as invasion, tumor growth, angiogenesis, and metastasis [87–91]. In addition to autocrine or paracrine signaling via HGF, c-Met may also be activated via the mutation, protein overexpression or amplification, or transcriptional alteration (via microRNA-mediated dysregulation) of MET [92–94]. c-Met overexpression and MET amplification are thought to be associated with a poorer prognosis in some types of tumors, including non-small cell lung cancer and gastric cancer [94]. In HOSCC, it has also been reported that c-Met expression is associated with cisplatin resistance and a strong propensity for metastasis *in vivo* [95], as well as a poor prognosis [96]. However, details of the involvement of c-Met in oral carcinogenesis are still unclear. Accordingly, we investigated how the relationship between the expression of c-Met and several tumor activation-related markers such as NF-κB is associated with oral carcinogenesis (data not shown). In addition, the expression and distribution of c-Met and NF-κB were also examined in HOSCC tissues (data not shown). The results of real-time qRT-PCR and immunoblot analysis indicated overexpression of c-Met mRNA and protein in SAS cells. Therefore, SAS cells were used in this study. To investigate how c-Met functions in SAS cells, c-Met knockdown analysis was performed. c-Met knockdown appeared to reduce the number of SAS cells. To confirm whether this had been due to apoptosis, caspase activity was then analyzed, and this revealed that apoptosis had indeed occurred via activation of caspases-9 and caspases-3/caspases-7 in SAS by c-Met knockdown. Furthermore, SAS showed cell cycle arrest at S/G2/M phase during this apoptotic cell death. Subsequently, to determine NF-κB expression after c-Met knockdown, we also used a siRNA approach to reduce the expression of c-Met and determine the effects on NF-κB activity. As expected, the level of c-Met mRNA was markedly reduced by c-Met siRNA. Moreover, c-Met knockdown by c-Met siRNA clearly decreased the activation of NF-κB mRNA in SAS cells, in comparison with controls. These data indicated that c-Met upregulated NF-κB activation and consequently that c-Met knockdown led to apoptosis of SAS cells. These combined data suggested that c-Met produced by autologous cancer cells promoted tumor growth. Furthermore, our *in vivo* studies demonstrated c-Metspecific immunoreactivity, consistent with the observation of NF-κB-positive cells in HOSCC biopsy samples (c-Met expression, 9/20 (45%); NF-κB expression, 18/20 cases (90%)). This result suggests that c-Met expression correlates with increased activation of NF-κB. Based on these in vitro and *in vivo* observations, it can be hypothesized that c-Met function leads to NF-κB activation and subsequently anti-apoptosis and that as a consequence, it may be associated with tumorigenesis, including growth, development, and angiogenesis in HOSCC.

Further investigations of the role of c-Met will be required to fully understand c-Met-mediated tumor proliferation and to establish a therapeutic strategy for c-Met-based oral cancer.


**5. Conclusions**

Polish MS patients surveyed during the first stage of the COVID-19 pandemic presented with a moderate to high level of perceived stress and preferred problem-focused coping strategies. The burden of the pandemic perceived by the patients was associated mainly with their social functioning and, to a lesser degree, with health status or health care services. The level of stress and coping profile showed more relationships with pandemic impact upon social issues than with disease-related variables. Consequences of the pandemic should be addressed with adequate support and counseling in management of MS patients.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/jcm10184215/s1, Supplementary Materials: Covid MS questionnaire.

**Author Contributions:** Conceptualization, A.P.-D., J.R. and S.B.; Methodology, A.P.-D., M.P. and A.R.-M.; Software, M.P. and T.P.; Validation, M.P. and A.R.-M.; Formal Analysis, A.R.-M., J.C.-Ł. and M.P.; Investigation, A.P.-D., J.C.-Ł., E.G. and M.P.; Resources, J.C.-Ł. and E.G.; Data Curation, A.P.-D. and T.P.; Writing—Original Draft Preparation, A.P.-D. and J.C.-Ł.; Writing—Review and Editing, J.R. and T.P.; Visualization, J.C.-Ł.; Supervision, S.B. and J.R.; Project Administration, A.P.-D.; Funding Acquisition, A.P.-D. and S.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** The study was supported with Wroclaw Medical University grant SUB.C 220.21.088.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee of Wroclaw Medical University (Ref. No KB-417/2020).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.