A theory of antenna performance in scatter-type reception

Many of the diversity techniques currently proposed or in use for scatter reception may be viewed as utilizing antenna systems with several adjustable parameters-typically two to four which are continually varied in response to fluctuations in the incident waveform, so as to maximize received power. An investigation is described which defines an ideal upper bound on performance of a linear variable-parameter antenna system in a scatter-type reception situation. The important results are 1) a standard for evaluation of antenna performance, and 2) deeper physical insight into the problem of antenna operation in scatter-type reception. A reception model is used in which the receiving antenna views a set of radio sources on a hypothetical celestial sphere. For each such set of sources possible, a "matched" antenna excitation exists which maximizes received power. Assuming random fluctuations in the radio source consistent with those observed in the transhorizon phenomenon, statistical properties of the received power are derived for the optimized antenna. Similar properties are then investigated for standard diversity systems. A significant "gap" is found to exist between the performance of existing or contemplated systems and the theoretical optimum.