Passive coherent location radar systems. Part 2: Waveform properties

Resolution and ambiguity in both range and Doppler are parameters of fundamental importance in the design and subsequent performance of any radar system. In passive coherent location (PCL) systems these properties are determined by the transmitted waveform, the location of the transmitter, the location of the receiver and the location of the target. Consequently, the scope for radar design and optimisation would seem to be severely restricted as many factors are not within the control of the radar designer. In this paper practical measurements of transmitted waveforms are reported and used to illustrate their effects on the resulting system design and performance. In particular the ‘self-ambiguity’ which enables the limits on range and Doppler resolution to be evaluated is computed. The bistatic form of the ambiguity function is subsequently presented and used to illustrate how these best case parameters vary as a function of transmitter, receiver and target locations. Understanding the forms that these functions can take and subsequently the implications for system performance is most important if this type of radar is to be used effectively. It is shown that the radar designer does in fact have some limited freedoms to improve system performance. Finally the implications of transmitter waveform and bistatic geometry on target detection, location and imaging are discussed.