Systematic Phase Codes for Resolving Range Overlaid Signals in a Doppler Weather Radar

Abstract

This paper deals with the recovery of Doppler velocities in the presence of range overlaid echoes. Transmitted pulses are phase shifted to tag the echoes from scatterers, which are separated by the unambiguous range. A new systematic phase code and an algorithm for estimating the mean velocities of overlaid first- and second-trip signals are presented. The return samples are phase corrected to cohere the first- or the second-trip signal, leaving the other signal power spread in a deterministic manner across the Doppler spectrum. An algorithm has been developed to recover the velocity of the weaker signal even if the power ratio of overlaid signals is as large as 40 dB, for spectrum widths of 4 m s?1 or less, and an unambiguous velocity of 32 m s?1. Tests on simulated weather signals indicate that the method, employed in surveillance Doppler radars, can effectively double the unambiguous range without the sacrifice of the unambiguous velocity interval.