Efficient utilization of virtual antenna motion

Switching among spaced antenna elements can be used for various purposes in software defined receivers (SDRs). Since this switching introduces delays between transmit and receive points, it produces locally-controlled virtual motion of the receiver and transmitter antennas relative to each other. This motion creates a direction- and velocity-dependent Doppler shift of the received signal relative to the transmitted one. Due to the capability to separate signals arriving from different directions, virtual antenna motion can be used for direction finding, navigation, surveillance, investigation of channels with multipath propagation, optimal reception of signals in such channels, spatial rejection of interfering signals, simultaneous reception of several signals arriving from different directions on the same frequency, etc. The use of virtual antenna motion for spatial rejection of interfering signals is considered in this paper. To properly utilize this motion, Doppler effect should be interpreted as time-frequency scaling of the received signals rather than their frequency shifts. It is proven that switching among the antenna elements at the receiver input prior to the frequency selection causes appearance of many out-of-band interfering signals within the receiver passband. An effective solution of this problem has been proposed. Another problem solved in this paper is efficient utilization of signal energy available on the antenna elements. Application of these solutions to spatial rejection of interfering signals and to decoupling of co-located receivers and transmitters is discussed.