High transfer-efficiency microsurface acoustic wave directional couplers

Surface acoustic waves (SAWS) directional couplers have long been known in both microwave and integrated acoustic applications. Such couplers, when both channels are of different widths and different dispersion characteristics, may also be used as electronic filters. SAW directional couplers are ideal for inclusion in acoustical signal processing devices, as modulators or switches. This article represents formulation and physical properties of advanced high transfer efficiency SAW directional couplers, using the coupled mode theory. One kind of directional coupler is especially considered and discussed in detail. The obtained coupling parameters are applicable to any guided modes in parallel waveguides of the same cross section, similar to 1/v index of refractive and identical shapes. Coupling constants and physical parameters for the coupled acoustic modes, computed according to this theory, are shown and seem to agree very well with experimental data.