Low-Loss Gigahertz Range Surface Acoustic Wave Filters using Harmonic Two-Phase Unidirectional Transducers

Abstract

The fabrication of surface acoustic wave (SAW) filters employing the conventional interdigital transducer (IDT) involves significant loss in the transmitted signals. An inherent problem in IDT is that the minimum insertion loss is 6 dB (1) owing to bidirectionality and strong passband ripple from triple-transit echo and secondary effects. To avoid these flaws and gain a simple structure of the filter, two-phase unidirectional transducers were chosen in this study. The fabrication of devices for frequencies above 1.5 GHz is still difficult and hence expensive. In this paper, a computer simulation model is built and used to study the frequency response of two GHz harmonic filters using unidirectional transducers. The proposed design provides moderate insertion loss. A simple model to find the input impedance of the proposed transducer is discussed.