Planar MESFET grid oscillators using gate feedback

A method for quasi-optically combining the output power of MESFETs in which drain and source leads couple directly to the radiated field is introduced. The design consists of a planar grid of devices placed in a Fabry-Perot cavity. Capacitive feedback is provided to the gate, allowing oscillation at much higher frequencies than previous grids. The oscillation frequency is dependent on the device characteristics, the resonator cavity, and the symmetries of the grid. A transmission-line model for the grid is discussed and used to design two oscillator arrays. A 16-element grid has produced 335 mW of power at 11.6 GHz with a DC-to-RF conversion efficiency of 20%. This design was scaled to produce a 36-element grid oscillator with output power of 235 mW at 17 GHz. These results represent a significant improvement in the performance of planar grid oscillators. The planar configuration of the grid is very convenient for monolithic integration and is easily scalable to millimeter-wave frequencies