Design of SAW expander and compressor on LiTaO₃ for a TCDMA spread spectrum system

We report on the design and performance of SAW minimum-shift-keying (MSK) tapped delay lines (TDL's) using pseudonoise (PN) code sequences of length 128 chips. As a substrate, LiTaO₃-X112°-rotY has been used due to the system requirements of a given CDMA/TDMA system (TCDMA). System IF frequency, bandwidth of the major lobe, and integration time were respectively 360 MHz, 63.5 MHz, and 3 μs. We used SAW TDL's employing non-weighted as well as cosine-apodized input transducers incorporating split-fingers. We designed both expander as well as compressor filters attaining very similar results. We found insertion loss values down to 16 dB and amplitude ripples of less than 2 dB. The close-in selectivity was 28 dB.