Acoustic wave bandpass electrical filters.

摘要

A surface acoustic wave bandpass electrical filter consists of input and output interdigital transducers (IP, OP) with an interposed track changing multistrip array (MSA). A conventional broadband array (MSA) is divided into two subgroups of strips with respect to a centre of symmetry (C) separated by different distances along the input track (T1) and the output track (T2) such that the amplitude-frequency response of the array (MSA) has a stopband centred on a predetermined frequency. If the input and output transducers (IP, OP) both have a double electrode configuration, electrode separation lambda o/4, providing a fundamental passband at a corresponding frequency fo and an equal amplitude passband at the third harmonic 3fo, then a separation difference of lambda o/6 between the sub-groups of the array (MSA) in the two tracks (T1, T2) can suppress the third harmonic passband in the filter output. The multistrip coupler may instead be divided into three sub-groups. The sub-groups of the multistrip array may be further sub-divided to suppress more than one frequency. Also a multistrip array arranged in groups to provide a shaped bandpass response may have each group divided into sub-groups to suppress a selected harmonic-passband of the array.