Low loss SAW matched filters with low sidelobe sequences for spread spectrum communications

A 300 MHz SAW matched filter with reduced mismatch-loss and with a coded transducer by a low autocorrelation sidelobe sequence has been developed for 1 Mbps SS weak radiation-power wireless communication modem. This low autocorrelation sequence of 25 chips was searched out to conform DS spreading DPSK signal. The sequence reduced output signal sidelobe 6 dB lower than 31 chip m-sequence, further obtained higher processing gain than that of Barker sequences. Furthermore, to reduce mismatch-loss in temperature stable SAW matched filters, a localized layered structure has been developed. ZnO is deposited only on the normal transducer on a ST-cut quartz substrate, reducing the mismatch-loss by 9 dB. A SS radio modem unit using this SAW matched filter shows a rather long transmission distance of about 20 m with a low current consumption 210 mA, considering such a high data rate 1 Mbps and the strict power regulation.