Acoustic resonator - surface acoustic wave filter with improved stop band attenuation at the upper stop band and low insertion loss

摘要

PROBLEM TO BE SOLVED: To reduce loss more than before, to improve high band side attenuation characteristics and to provide a filter smaller than before further in the resonator type surface acoustic wave filter of multi-ladder type circuit constitution for which serial arm surface acoustic wave resonators and parallel arm surface acoustic wave resonators are respectively constituted of surface acoustic wave resonators provided with an interdigital electrode and reflectors respectively provided on both sides of the interdigital electrode with a distance (t). ;SOLUTION: For serial arm surface acoustic wave elements 21a 21n, the distance (t) is defined to the value of the range of (n/2+0.55)λ₁-(n/2+0.81)λ₁. For parallel arm surface acoustic wave elements 23a-23n, the distance (t) is defined to (n/2+0.5)λ₂. The (n) is '0' or a positive integer and the λ₁ and λ₂ are the wavelengths of surface acoustic waves excited respectively by the serial arm surface acoustic wave resonators and the parallel arm surface acoustic wave resonators.;COPYRIGHT: (C)1997,JPO