 view of FIG. 3B, the diode circuit 110 is not shown, which makes the various metallization layers (e.g., pads) visible, such as pad 122.
[0053] According to embodiments, the mixer 100 can be optimized for a particular frequency range. For example, the width of the patterned metal features (e.g., filter widths) on the surface of the waveguide element 108 may be set to approximately 0.3-0.4 l, where l is the free-space wavelength. For instance, for operation at 375 GHz, the filter channel width may be approximately 0.3mm. In some embodiments, the mixer is optimized at one of 125 GHz, 250 GHz, and 375 GHz. While specific frequencies/wavelengths are provided in this example, the design and manufacture of the disclosed mixers may be optimized across a wide band of frequencies/wavelengths. For example, mixer 100 may be applicable as a mixer in the microwave, millimeter, and sub-millimeter ranges.
[0054] According to embodiments, the center part of the LO and RF filter arrangement is designed to be as wide as possible in order to minimize ohmic losses. In some embodiments, the width of the center line is 30%-50% of the width of the cavity in which the mixer is mounted. In some embodiments, the width of the center line is 50% or more of the width of the waveguide substrate. In some embodiments, the width of the line is between 0.1-0.2 l at the operating frequency. For example, for optimization at 375 GHz, the width of the center line running from the signal end to the IF output end may be approximately 100 microns wide.
[0055] In some embodiments, the patterned metal microstrip transmission line comprises a center line that extends from the diode circuit to the output and through one or more filter elements, the width of the center line is equal to or greater than 0.1 l and less than or equal to 0.2 l, the width of the suspended waveguide element is approximately 0.2 l, and the thickness of the substrate is 0.04 l. The housing cavity may have a width (e.g., in the transverse direction) of approximately.35 l (e.g., between 0.3-0.4 l), and the patterned microstrip transmission line is arranged in the cavity to couple an even transmission mode to a sidewall of the housing 132 cavity.
[0056] According to embodiments, the mixer 100 can be implemented without separate tuning stubs (e.g., wires) or a machined LO filter pin. This can be contrasted, for instance, with the design of WO 2007/125326, which requires one or more stub tuners in the form of extra wires as well as an orthogonal coaxial filter at the IF output to handle LO signal filtering.
[0057] According to embodiments, and in order to achieve the highest bandwidth in the RF and LO input circuit, an open circuit waveguide probe is used. This may provide an improvement, as short circuited waveguide are inherently narrow band, often resulting in poor power coupling across the desired band.
[0058] Referring now to FIG. 4, a method 400 of operating a mixer according to some embodiments is provided. The mixer may be, for instance, mixer 100 or any other mixer have features shown with respect to FIGs. 1, 2A, 2B, 3 A, 3B, and 6A.
[0059] The method 400 may begin with step s410, which comprises receiving an RF signal at a first input of a mixer apparatus having a suspended waveguide element, a plurality of suppression elements, and a diode circuit. In step s420, a local oscillator signal is provided to the mixer. In step s430, an intermediate frequency (IF) signal generated by the diode circuit is outputted. According to embodiments, outputting the IF signal comprises propagating the signal along a longitudinal direction of the mixer (e.g., mixer 100) through a plurality of filters. The filter may be, for example, a part of the plurality of suppression elements. According to some embodiments, the RF signal and LO signal are received and provided along a first axis with respect to the mixer, while the IF is output along a different, perpendicular axis.
[0060] Referring now to FIG. 5, a detection system 500 according to some embodiments is provided. In this example, an array of feedhorns 502 provide RF signal to one or more mixers 504, such as mixer(s) 100 described above. The RF signal can be mixed with a LO signal 512 from source 508, such as one or more Gunn oscillator sources. The resultant IF can then be fed to processing circuitry 506 for subsequent processing, including one or more of amplification, filtering, analog-to-digital conversion, and image generation. In some embodiments, the output IF is provided via a coaxial line from the mixers to one or more of the processing circuitry 506.
In some embodiments, the feedhorns 502, mixers 504, and signal paths (e.g., 512) can be housed in a block 514. A block for use with one more mixers described herein is illustrated, for instance, with respect to FIGs. 6A-6C. [0061] According to embodiments, the set of mixers 504 includes at least three types of mixers, where a first mixer is optimized a first frequency, a second mixer is optimized at a second frequency, and a third mixer is optimized at a third frequency. In this example, all types of mixers follow the design and configuration of mixer 100 as set forth in FIGs. 1-3. In some embodiments, the frequencies are 125 GHz, 250 GHz, and 375 GHz. In some embodiments, a fourth type of mixer is included using the design and configuration of mixer 100, which is optimized at 500 GHz.
[0062] Referring now to FIG. 6A, two machined halves of a detector block 600 are illustrated according to some embodiments. In this example, the first machined portion 602 can be combined with the second machined portion 604 to form a detector block. The block may comprise, for instance, the housing 132 of mixer 100 and block 514. As shown in FIG. 6A, each of the halves can include one or more feedhorn portions 606, which can serve as channels to deliver RF signals to a mixer 100. Each of the halves may also include input signal (e.g., LO) delivery portions 608, as well mixer cavities, shown in the detail 610. Additionally, and in some embodiments, the mixer can couple its output into a signal output 612 (e.g., containing a coaxial or other transmission line), which can be formed in the respective block halves such that a coaxial cable can run through the mixer housing 132. The output 612 may, for instance, carry IF signals generated by the mixer. According to embodiments, the feedhorns 606 and LO input 608 can be machined along the same axis (e.g., the x-axis) or in the same plane (e.g., the plane formed by the x- and z-axes). Additionally, in some embodiments, the mixer output 612 can be machined in a perpendicular/orthogonal fashion (e.g., along the y-axis). In this respect, the output signals from the mixer can be delivered in a different direction than the direction in which the input signals are received. For instance, signals may be output in a direction perpendicular to the plane in which signals are received.
[0063] Referring now to FIGs. 6B and 6C, one or more detector array blocks are illustrated according to some embodiments. These may correspond, for instance, to arrays 502 and blocks 514. A detector element, such as block 514 with an array of feedhorns 502, can be formed as a single block (e.g., as shown in FIGs. 6A and 6B). Also it can be formed from multiple blocks (e.g., with two sub-blocks as shown in FIG. 6C) to form a combined detection block with multiple rows and columns of feedhorns. Additionally, and according to embodiments, each sub-block can be formed from two parts as illustrated with respect to FIG. 6A, which shows the attachment of a half-block portion 602 with another half-block portion 604 to form block 600.
[0064] Referring now to FIG. 6B, a block 620 according to some embodiments is provided. In some instance, one or more of detector arrays 502 and block 514 may comprise block 620. Block 620 includes one or more signal inputs 622, one or more secondary inputs 624, and one or more outputs 626. For instance, signal inputs 622 may correspond to a plurality of detector feedhorns as illustrated in FIGs. 2, 5, 6A, and 9. Similarly, the secondary input(s) 624 may be an LO signal input, such as described with respect to FIGs. 2, 5, 6A, and 9. The output(s) 626 may be detected signal outputs, such as one or more IF signals from a mixer 100, as described in connection with FIG. 9, for instance. According to embodiments, the inputs are provided in the same plane while the outputs are provided in a transverse plane. In the example of FIG. 6B, the inputs 622, 624 are provided along the x-axis while the outputs 626 are provided along the y- axis. According to embodiments, processing circuitry may be connected to the outputs 626. For example, a plurality of processing circuitry units may be stacked in the z-axis direction to process the signals output from block 620. Likewise, additional blocks may be stacked in the z- axis direction to expand the detector. A similar arrangement is shown in FIG. 6C with elements 660a -n