Surface acoustic wave matched filter with dispersive substrate and saw group velocity based output electrode design

Abstract

A surface acoustic wave matched filter for use in a spread spectrum communication system is disclosed. The surface acoustic wave matched filter includes a substrate having dispersity and is composed of a sapphire main body and a piezoelectric aluminum nitride. A tap distance L of an output side electrode is designed on the basis of a group velocity vg instead of a phase velocity vs in order to match the tap distance L with an input spread spectrum signal and to improve a correlation peak level of an output demodulated signal. When the tap distance L is set to satisfy a condition of vg/f1×0.97≦L≦vg/f1×1.02, a decrease in the correlation peak level of the matched filter can be improved from 7 dB to a value smaller than 3 dB, and S/N of the output demodulated signal can be increased. Thus, the disclosed device renders it no longer necessary to process the output demodulated signal by a complicated and power consuming circuit.

Dependencies are inferred from the claim text.