Frequency stability in adaptive retrodirective arrays

The frequency stability of communications or remote sensing systems using phase conjugation as a means of retrodirective signaling is developed under the influence of constant rectilinear motion. The results indicate that for dynamic mobile platforms such as aircraft, helicopters, and ground vehicles the retrodirective properties of phase conjugating arrays are not guaranteed due to a possible instability of the frequency. It is shown that the frequency transmitted by each platform has a dependence on the open loop gains of the transceivers on each platform in the link. Fast and accurate reconstruction of the phase of the signal requires a high open loop gain, however, too high a gain will cause instability and eventual loss of lock. Design tradeoffs are discussed.