Low insertion loss surface acoustic wave matched filter with low sidelobe sequence and its application for spread spectrum communication

For direct sequence (DS) spread spectrum communication systems with differential phase-shift keying (DPSK) modulation, we have calculated low autocorrelation sidelobe pseudo noise (PN) sequences. We constructed a matched filter comprising localized layered structure on a quartz crystal to obtain low matching loss. As a result of the sequences and the construction, 14 dB (6 dB improvement on that of the conventional sequences) peak vs sidelobe of correlated output signal and 9 dB lower loss than that of a conventional filter was achieved. We have applied these matched filters to SS rf-modem units for weak-power digital communications. In these modem units high data rate (1 Mbps), long communication distance (about 20 m) and low current (210 mA when received) performances are obtained.