High Power Spatial Combiners: Tile and Tray Approaches

Abstract

Spatial power combining is a method of coherently combining the power of manyamplifying devices using free space as the power dividing/combining medium in contrastto traditional circuit based combiners. The spatial combiner is formed from anarray of amplifying unit cells, with each cell receiving a signal, amplifying it, and thenradiating it into free space. Two methods of spatial powercombining, tile and tray, are investigated in this thesis.The tile-based spatial combiner consists of a thick groundplane with receiving microstrip patch antennason one side and transmitting microstrip patch antennas on the other. In addition, amplifiers are placedon both sides of the thick groundplane, which provides efficient heat removal.This research is focused on the optimal array spacing, biasing,and feeding of tile-based arrays to achieve high output power levels atKa-band (Lockheed Martin was specifically interested in achieving greater than 25 Watts ofradiated power under a DARPA MAFET-3 program). Several arrays were developed, consisting of13, 45, and 98 elements. Noteworthy results were obtained from theexperiments with this design approach. A tray-based approach is also investigated in this thesis. This approach differsfrom the tile-based approach by having multiple groundplanes (trays) containingamplifiers stacked to form an array of amplifying unit cells. In addition,microstrip patch antennas are placed at the ends of the trays and radiate in an end-fire pattern with respectto the tray containing the amplifiers. For this purpose, an approach has been developedfor the feeding of the microstrip patch antennas. This feeding mechanismallows the amplifiers and radiating elements to be isolated. Thus moreroom is allowed for the amplifiers, while minimizing coupling that may causespurious oscillations. An X-band and Ka-band array have been developed, consisting of 25 and 49 elements, respectively. Both arrays provide efficient heat sinking through thick metal groundplanes. In addition, an experimentalanalysis on the array tolerance to device failure has been performed on both tray-basedarrays. This study examines the effect of device failure on the gain, power output, and radiationpattern.