QUADRAPHASE UNIDIRECTIONAL SURFACE ACOUSTIC WAVE INTERDIGITAL TRANSDUCER

It is indicated that in comparison with three-phase unidirectional transducers and group-type unidirectional transducers the quadraphase unidirectional surface acoustic wave transducers (QPUT)³ are superior in directionality, suitable to the wideband low-loss filters. The equivalent circuit, acoustic radiation conductance, static capacity and frequency response of QPUT are derived, and the simple quadrature phase shift network and its influence on the frequency response are given. Thus, a rather complete design theory of QPUT are obtained.
A filter of insertion loss less than 0.72 dB is obtained by a uniform QPUT. The pas-sband ripple could not be observed by the instrument with division of 0.1 dB. The experimental frequency response agrees with the theoretical one very well.