Suppressed ambiguity in range by phase-coded waveforms

In Doppler radar for surveillance and remote sensing, the ambiguities in range/Doppler are usually solved by varying the pulse repetition frequency. In this paper, two alternative methods are discussed based on phase-coding and orthogonal waveforms. The first one distributes a phase code over a pulse sequence with only one phase step per pulse. The received pulses are correlated with the phase code sequence, and by varying the delay of the phase code, the subintervals in range are scanned and reflector responses outside the focused range interval become highly suppressed. The alternative method that was studied applies a set of near-orthogonal phase codes, which modulate the pulses transmitted. In the receiver, the different subintervals in range are scanned, or detected in parallel, by correlating the signal from the scene by the delayed code sequence of the pulse transmitted. Because orthogonal codes are used, a strong suppression is achieved for signals originating outside the focused subinterval in range.