Effect of waveform coding on stepped frequency modulated pulsed radar transmit signals

Abstract

The choice of a waveform in a radar system plays a predominant role in characterizing the radars’ ability to differentiate two closely spaced targets in both range and Doppler domains. RADAR waveforms are broadly categorized into two types, viz. pulsed or continuous waveform. A waveform can be analyzed in both time and frequency domains. The frequency domain analysis informs about the range and Doppler resolution of the radar target. The ambiguity of the transmitted waveform in both range and Doppler domain is used to understand the critical parameters used in the design and performance of any radar system. Precise radar measurements like range and Doppler calculation need higher resolution in both domains. But, in a pulsed radar system, there is an important factor of trade-off between range resolution and sensitivity, that necessitates pulses of smaller width, while the pulse energy in the transmitted waveform requires a longer pulse duration. An approach to overcome this trade-off is pulse compression which modulates the pulses to be transmitted. In the work reported here, a new approach to pulse compression technique is provided by modulating the transmitted waveform of a stepped frequency waveform (SFW) with orthogonal frequency-division multiplexing (OFDM). The reported work evaluates the performance of frequency spacings that are either uniform or non-uniform in the SFW waveform in terms of their maximum detection capability, observed from the graphs of delay and Doppler cuts in the ambiguity function plot. Various phase coding techniques are also used to define the non-uniform spaced SFW. The robustness of radar waveforms in terms of their static and dynamic resolution parameters, as well as their ambiguities, is also evaluated.