The use of polarisation coherency in the detection of radar signals

Electronic support measures (ESM) receivers are used to try to intercept and detect radar signals. ESM receivers can detect most current radars easily, because these types of radar emit short-duration, unmodulated, narrow-bandwidth, high-peak-power pulses. ESM receivers tend to be well matched to such waveforms. However, current ESM receivers have much more difficulty in detecting low probability of intercept (LPI) radar signals of which they have no a priori knowledge. The authors are concerned with the specific problem of the detection of LPI radar using a ship-board ESM-set in a “blue water” scenario. It is assumed that, at any one time, there will be at most one LPI radar emitting, and the environment will be clean (no interference or multipath etc.). The detection of a completely unknown LPI radar signal is the only concern, and analysis to ascertain the type of waveform being used is not considered. The work is aimed towards signal detection with as low a signal-to-noise ratio as possible, which would give the earliest possible warning of radar activity