Resonator to exert - ladder-type electric filter with acoustic surface waves

摘要

PROBLEM TO BE SOLVED: To obtain a sufficient and flat frequency characteristic with a wide pass band width without spurious within a pass band by defining the thickness of a metallic film as the specified percentage of an electrode period in IDt of parallel arm surface acoustic wave resonator. ;SOLUTION: In the parallel arm surface acoustic wave resonator 5 consisting of a pair of interdigital transducers IDTs which exciting surface acoustic wave, the width of the electrode finger of IDT is defined as Lm, the gap width of the electrode finger is as Lg and it is defined that η=Lm/(Lm+Lg). When ηbecomes larger than 0.5, a ripple within the pass band becomes larger. When ηbecomes smaller than 0.5, the ripple becomes smaller. When η becomes smaller than about 0.3, the electric resistance of IDT becomes larger with the rapid increase of an insertion loss and the frequency characteristic of the filter becomes inactive os that the ripple becomes large quickly. Therefore, it is necessary to set η to be 0.2≤η≤0 in order to make the ripple small with the ripple within the passage band where n is 0.5 as reference. At the time of this state, the sufficient frequency characteristic is obtained.;COPYRIGHT: (C)1997,JPO