Synthesis of acoustic-surface-wave-resonator filters using any of various coupling mechanisms

Abstract

Design of surface-wave resonator bandpass filters from lumped-element low-pass prototypes is treated by use of a generalized version of Cohn's direct-coupled filter theory. Equations are presented for straightforwud application of the method to the design of SAW resonator filters with acoustic-array couplings, transducer couplings, or multistrip couplings. To illustrate this technique, a four-resonator filter with a given Chebyshev response is set as an objective, and several designs were worked out for such a filter, each using different coupling arrangements. The responses for the various designs were computed, and though an met the given passband specifications, some are seen to have stronger stopband attenuation than others. Conclusions are drawn with regard to the range of application of the various types of couplings. The derivation of the equations needed for the design of acoustic-array and multistrip couplings is outlined in appendices.