A SAW shaping filter for high data rate MSK-encoding in a broadband DS-CDMA system

We report on two surface acoustic wave (SAW) shaping filters which generate a minimum shift keying (MSK) modulated signal by converting a BPSK modulated signal. The filters are intended to be used for modulators with high data rates, as it is necessary in broadband direct sequence code division multiple access (DS-CDMA) systems. One filter has been fabricated from a lithium tantalate (LiTaO/sub 3/) substrate, and one from a quartz substrate. The filter on LiTaO/sub 3/ fulfills all requirements dealing with spectrum shaping. However, the temperature range is not as wide as with quartz substrates due to the higher temperature coefficient of LiTaO/sub 3/. The filter on quartz is very stable from the temperature coefficient point of view, but the insertion attenuation and spurious electromagnetic feedthrough are relatively high.