Indicating Hypersonic Moving Targets Based on A Phase Coded Waveform with High Doppler Tolerance and Low Sidelobe Levels

The ultrafast motion of hypersonic flight vehicles will lead to a large Doppler frequency shift in the echo, thereby contributing to severe mismatch loss during pulse compression that poses great challenges on achieving precise detection and indication of them for radar systems. To deal with it, a unimodular waveform with high Doppler tolerance and low sidelobe levels referred to as HDTLS is first introduced in this paper. Therein, an optimization model that is able to control the peak mainlobe and sidelobe levels under Doppler shifts according to a Pareto weight is presented, and the memory-less Broyden-Fletcher-Goldfarb-Shanno (MM-BFGS) algorithm is adopted to address its minimization problem. Then, it is known that most of Doppler-tolerant waveforms are with a diagonal-ridge-type ambiguous function, and thus there inevitably appears the presence of range-Doppler coupling. Consequently, to correctly indicate the hypersonic moving targets, two schemes for separately estimating the Doppler shifts and time delay are further proposed. Specifically, we employ the difference in spectrum modulus between the transmitted and received signals to realize the measurement of Doppler frequencies without being influenced by time delay. And then, the ranges of moving targets are estimated by approaching the extra linear phase function of the echo spectrum after Doppler compensation. In the end, a number of experiments are conducted to demonstrate the superior performance of the proposed waveform in comparison with the state-of-the-art ones and the effectiveness of the designed parameter estimation methods.