Frequency-dependent behaviour of an acoustic-surface-wave multistrip coupler

Abstract

The distribution of acoustic intensity within a surface-wave multistrip coupler on lithium niobate has been observed using a laser probe. The number of metal strips required for complete transfer of energy between coupled tracks has been determined as a function of acoustic frequency. Two stopbands were observed in the frequency range explored. A simple analytic expression is presented which is in good agreement with experiment away from the vicinity of the stopbands. It may be regarded as useful for coupler design; it is used to demonstrate that the 3 dB fractional bandwidth of the coupler may exceed 120%.