An active retrodirective array for satellite communications

The concept and design of an active retrodirective array, resulting from the specialized requirements and constraints of space/earth communications, is presented. The advantages of employing active microwave gain are discussed. The attendant problem of instability is defined and several aspects of the solution, namely frequency offsetting and polarization isolation, are detailed. The latter technique makes use of orthogonally polarized "subarrays" -one for receiving and one for transmitting-intermeshed on a common aperture surface. A discussion of tolerable phase errors and the effect of element failure on the system reliability is presented. Techniques for realizing the active circuitry required for the functions of RF amplification, frequency conversion and modulation are described. An experimental model, employing strip transmission line techniques throughout, was fabricated and tested. All results, including those of array gain, retrodirectivity and simultaneous retrodirectivity from several sources at different frequencies, and effects of element removal, corresponded closely to their calculated predictions.