Using of self-resonance approach for high selectivity low loss SAW filters

Low loss high selectivity surface acoustic wave (SAW) filters realized on the basis of the self-resonance approach without the use of matching LC-networks are presented. This approach is based on input interdigital transducer (IDT) static capacitance compensation by radiation susceptance and the choice of a definite number of finger pairs. Self-resonant SAW filters are developed on the basis of a ring configuration with reflecting multistrip couplers (RMSC) and unidirectional IDTs with U-shaped multistrip couplers. The optimization of filter topologies is achieved using computer programs based on the equivalent circuit model. At 45 MHz the ring filters show insertion loss below 2 dB, 2-5% fractional bandwidth, and stopband attenuation over 50 dB