OVERVIEW

As defined in Chapter 1, a multistatic radar uses two or more receiving sites with overlapping coverage and combines target data coherently or noncoherently at a central location. Examples of noncoherent data combining are SPASUR [1,7, 184, 185] and the MMS [13, 14] although for both Systems, each transmitting-receiving pair operates coherently; that is, each receiver establishes phase coherence with the transmitter and coherently processes the bistatic echo. Examples of coherent data combining are thinned, random, and distorted arrays [3-6], the Radio Camera [11, 12], and interferometers, such as SPASUR when it operates in a calibration mode by cross-correlating radio star signais. Multiple transmitters can also be used, but they are not essential to the definition. When multiple transmitters are used and the transmissions from each site are coherently phased so that the multiple transmitters operate as a single transmitting array, the configuration is called a distrib-uted array radar (DAR) [3, 5].

When the multistatic receiving sites are widely separated, the bistatic echo from complex targets at each receiving site can become spatially decorrelated; that is, a different phase and amplitude of the bistatic echo will be received by each site. When the multistatic radar combines data noncoherently, the system's S/N is improved by noncoherent integration of the decorrelated signais [225-228]. This process is analogous to signal decorrelation by frequency agility in a monostatic radar. For example, a target exhibiting Swerling 1 or 3 fluctuation statistics at one frequency (or site) might exhibit Swerling 2 or 4 statistics...