SAW fixed-code matched filters for wireless spread spectrum consumer communications

We report on the design and performance of SAW MSK fixed-code matched filters using PN code sequences of length 128 chips. As a substrate, lithium tantalate has been used due to the system requirements of a given CDMA/TDMA system. The integration time was set to 3μs. We designed matched filter versions with two center frequencies 267 MHz and 360 MHz having bandwidths of the major lobe of respectively 65.7 MHz and 63.5 MHz. We used SAW tapped delay lines employing non-weighted as well as cosine-apodized interdigital transducers. Split-fingers with a metalization height of 150 nm (aluminum) were used. We attained insertion loss values down to 18 dB (@ 267 MHz) and 16 dB (@ 360 MHz). Amplitude ripples were less than 1 and 2 dB, and the close-in selectivity was 23 dB (@ 267 MHz) and 28 dB (@ 360 MHz).