Evaluation of pulse compression techniques for X-band radar systems

Abstract

Detection of moving targets using a moving target indication (MTI) type radar system has two important tasks viz., determination of the precise range and the velocity of the target. Precise range calculations require the radar system to have a high range resolution ability. An important trade-off factor in radar systems is between range resolution, that requires shorter pulse, and transmitted pulse energy, that necessitates longer pulses. Pulse compression is a technique that helps overcome this tradeoff by modulating the pulses to be transmitted. Various frequency and phase modulation techniques can be used to achieve compression of the pulses. In the discussions here, the linear frequency modulation (LFM) and non-linear frequency modulation (NLFM) methods are compared with phase modulation techniques such as Barker codes and polyphase codes. Two new approaches for pulse compression that employ quadrature phase-shift keying (QPSK) and quadrature amplitude modulation (QAM) are also presented. These pulse compression techniques are compared for relative performance using parameters such as the peak-sidelobe ratio (PSLR), pulse compression ratio and Doppler tolerance. Results show that polyphase codes have high Doppler tolerance. QAM and QPSK, like polyphase codes, are not limited by number of bits that can be used within a pulse, and thus can be used to achieve good compression ratios.