BEAM-PROPAGATION ALGORITHMS FOR FREQUENCY-RESPONSE OF SURFACE-ACOUSTIC-WAVE DIRECTIONAL-COUPLERS

Surface acoustic wave directional couplers have long been known in bot h microwave and integrated acoustic applications. Such couplers are id eal for integration in acoustical signal processing devices, such as m odulators or switches. There are, however, very few publications conce rning the frequency response of these devices. This article represents both experimental and theoretical studies on the frequency response o f directional couplers, with and without a thin strip deposited in the gap between the main channels. The beam propagation method, used in i ntegrated optics, was adapted for acoustical directional couplers. It enabled the analysis and prediction of the frequency response of these types of couplers. Calculations were performed for the channels and i nterdigital transducers in the frequency range of 50-90 MHz. By using proper dimensions of the couplers? parameters, coupling efficiency for the higher part of the frequencies, in the receiver channel, was incr eased. This increase enables the selection of receiver frequencies and , therefore, a frequency channelizer could be developed. A thin strip between the main channels increases the coupling efficiency between th e two channels and thereby reduces by about 30% the length of the coup ler required for different frequency selections or conventional switch es. This reduction makes it possible to obtain more compact devices wi th reduced losses. (C) 1996 American Institute of Physics.