IDT EXCITING LONGITUDINAL COUPLING TYPE DUAL MODE FILTER

摘要

PURPOSE:To attain the filter with broad band and low loss by arranging two interdigital transducer(IDT) electrodes in series on a piezoelectric substrate along the propagation direction of a wave stimulated by them, arranging plural shield electrode fingers between both the IDTs and arranging a reflector at the outside of both the IDTs. CONSTITUTION:The IDTs 2, 3 whose electrode finger period is LT are arranged on the piezoelectric substrate 1 so as to satisfy the relation of IDT interval la(m+1/4)LTla(m+1)LT, m-set of shield electrode fingers 4', 4',... whose electrode finger period is LS between the IDTs 2,3, and reflectors 5, 6 whose electrode finger period is LR are provided at the outside of the IDTS respectively and the relation of the electrode finger periods LS, LT, LR is selected as LS LTLR. Thus, the filter characteristic with a broad band and a low loss is obtained.