Frequency response of surface acoustic waves directional couplers

Surface Acoustic Waves (SAW) directional couplers have long been known in both microwave and integrated acoustic applications. However, there have been very few publications concerning the frequency response of these devices. This paper represents both experimental and theoretical studies on the frequency response of directional couplers, with and without a thin strip deposited in the gap, between the main channels. Beam propagation method (BPM), adapted from integrated optics, was used to analyze the frequency response of this type of couplers. Calculations and measurements were performed in the frequency range of 50-90 MHz. By using proper dimensions of couplers parameters, the efficiency of coupling for the higher part of the frequencies, in the receiver channel, was increased. 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 the two channels and, therefore, reduces by about 30% the length of the coupler required for different frequency selections or conventional switches. This reduction makes it possible to obtain more compact devices with reduced losses.