Miniaturized planar antenna with NANOMET powder cores for the VHF band application
In recent years, the need for antennas with small size, light weight, and low profile have been continuously growing in modern wireless communication systems. The wavelength for the VHF band frequency of 300 MHz in free space is about 100 cm, and traditional antennas that operating at this frequency would be too large to be used for a wireless terminal. In order to reduce the antenna size, several different ways are reported recently. External lumped elements, such as capacitors and inductors, are used in the antenna design to reduce the antenna dimension. But lumped elements not only increase the fabrication cost but also decrease the antenna efficiency. The idea of shorting the radiating part of the antenna to the ground plane is introduced to miniature the antenna. This method also makes the antenna more stable to external influence. A straightforward way by using special substrate material with high relative permittivity is applied to reduce the antenna size. However, antennas with high permittivity substrates will result in decreased bandwidth and the excitation of surface waves leading to lower radiation efficiency.