Suppression of gating sidelobes

Surface acoustic wave devices are frequently used in FM pulse expansion and compression systems. These devices are usually used in conjunction with a time gate and limiter following the expander and a weighting filter such as a Hamming filter after the compressor. For moderate compression ratios (time bandwidth product), this results in undesirable gating sidelobes. It is shown that the level of these sidelobes can vary by up to 6 dB depending on the response of the SAW devices outside of their desired bandwidth. In order to reduce the in-band ripple, SAW devices are usually built with more fingers (when using interdigital chirped combs) or more grooves (when using chirped reflective gratings) than necessary to provide the required bandwidth. It is important to consider the effect of this excess bandwidth on gating sidelobes when designing systems using such devices. It is shown that best results occur when the excess bandwidth of the compressor is filtered out and the excess bandwidth of the expander is not removed.