Phase Modulated Waveforms for Transponder-Based Radar Sensing: Signal Optimization and Experiments

Both the theoretical and engineering aspects of using transponder-based signal waveforms, such as pulse-position-modulated 1090-MHz Automatic Dependent Surveillance-Broadcast, for noncooperative target sensing are discussed in this article. The random binary phase modulation coding technique is applied to the original transponder signal waveforms to improve the autocorrelation and sidelobe performance. A detailed study of the characterizations of this waveform and its potential for target detection is presented. The impact of random phase coding is analyzed from both signal spectrum (based on stochastic signal model) and radar ambiguity functions (based on deterministic signal model). The combination of pulse-position modulation and maximum length binary random phase coding sequence is shown to have satisfactory performance. In terms of optimal receiver, the traditional correlation receiver (or matched filter) and mismatched filters with different criteria are analyzed. The tradeoffs of receiver design for transponder-based radars are discussed. The experimental implementation of a transponder-based radar sensor with arbitrary waveform generator and commercial, off-the-shelf components is introduced and discussed. The experiment results show that noncooperative target detection using such a radar sensor is feasible with appropriate design of waveforms, system architecture and signal processors.