Longitudinal triplex mode saw filter

TLDR: In this paper, a longitudinal SAW filter in which ripple and a difference from group delay times are limited by obtaining a pass band depending on three primary - ternary vibration modes in three input/output interdigital transducer electrodes (IDT).

Abstract: PURPOSE: To obtain a longitudinal SAW filter in which ripple and a difference from group delay times are limited by obtaining a pass band depending on three primary - ternary vibration modes in three input/output interdigital transducer electrodes (IDT). CONSTITUTION: Input/output electrodes 11, 12 of nT pairs respectively are arranged on a major surface of an ST-cut crystal substrate 1 along a propagation direction of a SAW(surface acoustic wave). Furthermore, a 3rd center IDT electrode 13 of nG pairs is arranged between the electrodes 11, 12 and reflectors 5, 6 having N sets of gratings are arranged at both sides of the three IDT electrodes. The electrode finger pitch of the IDT electrodes 11, 12, 13 is identical to each other, the grating pitch of the reflectors 5, 6 is set a little larger than that of the IDT electrodes to improve the reflecting efficiency and to attain the filter with a low loss. Then the interval between the IDT electrodes is to be an integral number of multiple of the electrode finger pitch the interval between the IDT electrode and the reflector is selected to be a half wavelength of a stimulated SAW and the primary - ternary vibration modes are confined between the reflectors 5 and 6. COPYRIGHT: (C)1994,JPO&Japio