Ka-Band Wideband-Gap Solid-State Power Amplifier: General Architecture Considerations,” The Interplanetary Network

Millimeter-wave power-combining techniques are reviewed, and three architec-tures are chosen for further analyses. Although microstrip binary and serial com-bining are the most straightforward techniques to implement, they generally suffer from excessive circuit loss. To maximize combining efficiency, we therefore chose three architectures that use low-loss waveguide structures. The first architecture is based on non-resonant radial combiners and offers the greatest flexibility in the number of ports combined. It may be possible to combine up to 200 monolithic microwave integrated circuits (MMICs) with a combining efficiency>70 percent. The second architecture is based on a more conventional corporate combining de-sign using a low-loss waveguide adder. Initial simulations indicate an insertion loss of 0.1 dB per adder, and greater than 30-dB port-to-port isolation may be possible. The third architecture is based on an oversized coaxial spatial combiner. Although all three architectures offer some flexibility, the approximate MMIC requirements are 1 to 4 W and>55 percent power-added efficiency. These power levels are on the upper range for gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) technology, but are expected to be easily achieved with gallium nitride (GaN). The high efficiency, however, seems beyond the reach of GaAs and will require a focused research effort for GaN