Detailed Investigation on the Group-Type Unidirectional Inter-Digital SAW Transducer with its Application to Low Insertion Loss Surface Wave Filters

Filters employing the standard two-transducer configuration have an inherent 6 dB minimum insertion loss due to bidirectionality. Furthermore, they show a strong passband ripple owing to various reflections between the electrodes. In this paper, the applicability to very low insertion loss SAW filters of a recently proposed group-type unidirectional inter-digital transducer (GTIDT) is examined. Good agreement was found between theoretical and experimental data. A filter with minimum insertion loss of 1 dB without tuning and a passband ripple of less than 0.2 dB could be fabricated.