Microwave Network Analyses of Surface Acoustic Waveguides - II. Rectangular Ridge Guides

Abstract

Ahfruct-The microwave network approach to the solution of guided acoustic wave problems was applied in Paper I to two examples of the class of flat overlay guides: the strip and the slot guides. In this paper, the methods are applied to two different rectangular ridge StNChIeS, the well-known topographic ridge guide and the newer overlay ridge guide. In contrast to the flat overlay guides, for which good analytical results were previously available, no other analytical results have been published for the ridge guides which furnish good accuracy (although excellent numerical methods have been described). In addition, little information is available elsewhere on the pseudo-Rayleigh mode of the ridge guides, which is treated here in detail, and the overlay ridge structure itself is a new one whose properties are not yet appreciated. N THE COMPANION paper [l81 , a microwave network approach was presented for the analysis of waveguides for acoustic surface waves. The philosophy underlying this new approach was discussed, the basic features of the method were presented, and the method was applied to two examples of flat overlay waveguides, the strip and the slot guides. In the present paper, this method is applied to a different class of waveguides: rectangular ridge guides. The rectangular ridge waveguides themselves are of two types: the topographic ridge guide, for which the ridge and the substrate are composed of the same material, and the overlay ridge guide, in which the ridge is comprised of a material different from that of the substrate. The two structures are shown in Figs. l(a) and l(b). Both of these ridge guides are fundamentally different from the strip and slot guides, which appear respectively in Figs. l(a) and l(b) of Paper I. In the latter two guides, thin platings are employed to perturb the Rayleigh mode of the substrate, with the result that almost all of the energy in the waveguide mode resides in the sub