Active grids for quasi-optical power combining

Active grids are periodic structures loaded with transistors or diodes that interact with electromagnetic beams. These new quasi-optical components may make possible a new generation of low-cost, high-power solid-state millimeter-wave communications, broadcast, and radar systems. Quasi-optical power combining allows the output power from large numbers of individual transistors and diodes to be combined in free space without transmission-line losses. These components can often be made as planar structures that are suitable for large-scale monolithic integration. A variety of grids have been demonstrated, including detectors, phase shifters, multipliers, oscillators, and more recently, amplifiers and switches. In these grids, the power is proportional to the area, while the circuit impedances are determined by the dimensions of the unit cell. This allows great design flexibility. One can achieve high power and high efficiency simultaneously, or large dynamic range and low noise at the same time. The authors discuss the results for several grids. The first is a a doubler with an output power of 330 μW at 1 THz. The second is a 10×10 pHEMT hybrid grid amplifier with a 3 dB noise figure and 3.7 W output at 10 GHz. They also discuss current results on monolithic grid amplifiers for millimeter wavelengths