Ferrite Rotary-field Phase Shifters: A Survey Of Current Technology And Applications

fits the descriptor “rotary–field” well, has been used in a number of antennas with single–axis phase scanning, where high phase accuracy and/or the ability to handle moderate amounts of r–f power is important. A summary of performance statistics on a group of medium power (40 KW. peak, 600W. average) S–Band rotary–field phase shifters is available from the literature [6]; these units operated with typical rms phase errors on the order of 0.75° and average insertion loss around 0.35 dB. As with most human endeavor, arriving at a hardware realization of the rotary–field phase shifter was achieved only after dealing with a host of design parameters, each of which had to be optimized to some degree, in many cases compromising other parameters. In the original production design for the AWACS antenna, much of the optimization was done empirically, because of the novelty of the approach, the effective lack of computational models, and the program schedule demand for a timely solution. The success of that effort is measured by the fact that the design still remains at the state–of–the–art with respect to performance, and that virtually all of the hardware items delivered have remained in service without failure, in some cases for a period now exceeding twenty years. While r–f characteristics have not been substantially improved, understanding of the design considerations has increased very greatly, and some simple computational models have been developed for predicting the performance of trial designs. The material presented below discusses a few selected topics affecting performance, and also reviews the extensions in device application at lower frequencies and higher power levels that have recently been achieved through the use of filter–like geometries of alternating ferrite and ceramic dielectric disks in place of the simple ferrite rod half–wave plate.