When a bistatic receiver is designed to operate directly with a cooperative mono-static radar, it is called a hybrid radar, and can sometimes improve the performance of the monostatic radar when compared to the performance of two netted mono-static radars. The principal example is countering three types of retrodirective ECM Systems: retrojammers, augmented decoys, and active cancellation. This hybrid radar configuration exploits two bistatic features for performance enhancement: spatial diversity, or transmitting-receiving site separation, and covertness, because the second site must be quiet to counter the retrodirective ECM operation. In some hybrid configurations, the bistatic receiver can be a second monostatic radar that operates in the receive-only mode. When a hybrid radar is configured to counter a retrodirective ECM System, it is sometimes called a "counter-retro" System. (Of course, a bistatic radar by itself is also a counter, but these radars are seldom used alone.)
A retrodirective ECM System operates by measuring the AOA of a signal, usu-ally a radar signal, and transmitting maximum or minimum power at that AOA. A retrodirective jammer, or retrojammer, is a typical example of a System transmitting maximum power. It might use a high-gain multibeam antenna when receiving and transmitting. A signal received on one beam identifies the AOA. The jamming signal is then retrodirected in the colinear transmit beam back to the signal source [192, 233]. The retrojammer operates as a self-screening escort or standoff Jammer and can transmit noise or deception waveforms. The jammer's ERP is, of course, enhanced...
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