SAW composite longitudinal mode resonator (CLMR) filters and their application to new synthesized resonator filters

Abstract

Digitalization of mobile communication systems requires SAW IF filters with high performance such as low loss, broader band width, flat group delay, steep filter skirt and high rejection level simultaneously. In order to realize such performance, a new resonator filter design technique and two other modified techniques have been developed to synthesize the filters. This paper describes the new design method for the filters. First one is the composite longitudinal mode resonator (CLMR) filter, which utilize three different longitudinal modes and expand the bandwidth more than twice the conventional one. Second one is two dimensional coupled mode SAW resonator (2D-CLMR) filters, which utilize longitudinal modes and transversely coupled modes simultaneously and synthesized multi mode resonance to obtain broader bandwidth, steeper filter skirt and higher out-of-band rejection. The third one, which is equivalent to the second one, is electrically synthesized CLMR filters, which are composed of two electrically connected CLMR filters instead of single 2D-CLMR filters. Several experiments have been made at 250 MHz and the results of new filters with insertion of less than 3 dB and relative bandwidth of about 0.15 percent are obtained with excellent filter skirts