Quasi-optical planar grids for microwave and millimeter-wave power combining

Solid-state devices that produce radiation in the microwave and millimeter-wave region of the electromagnetic spectrum have relatively low power outputs compared to their electron-tube counterparts. In an attempt to obtain more power from solid-state sources, a number of power-combining schemes have been developed through the years. One of the most promising techniques involves superposing the outputs of many devices in free space. This quasi-optical approach has several advantages: the losses associated with waveguides and feed networks are eliminated, the power can be distributed over a large number of devices, and an external phase-locking signal is unnecessary. In this work, a method for quasi-optical power combining which is based on integrating devices into periodic grids is discussed. The approach is relatively simple to implement because the grid structures are planar. Thus they easily accommodate solid-state devices and allow for the possibility of wafer-scale integration. A method for analyzing the grids is presented and used to derive models for a variety of configurations. The validity of these models is investigated using a quasi-optical reflectometer. Designs and experimental results for MESFET oscillator grids operating in X-band and Ku-band are examined and discussed in detail.