Low probability of intercept (LPI) techniques and implementations for radar systems

After a brief overview of optimal low-probability of intercept (LPI) radar design criteria, it is shown that for a given radar signal code length, many more codes are available by using higher-order Galois fields; that is, polyphase coding will supply the required diversity. Various aspects of polyphase coding are described because Doppler compensation of the returned signal is a polyphase process. It is shown that radiated spectral components are minimized if the code modulation is restricted to codes that have two-level autocorrelation functions. In addition, polyphase code modulation assignments allow the peak correlation sidelobes to be minimized in contrast to biphase coding that relies only on the best choice for the starting code element. The RMS sidelobe values are likewise reduced, so clutter rejection is actually improved with polyphase coding