Acoustic wave bandpass electrical filters.

摘要

A surface acoustic wave bandpass electrical filter has double electrode input and output transducers (IP and OP) whose combined amplitude-frequency response has a fundamental passband centred on a frequency fo and a corresponding third harmonic passband. An interposed multistrip coupler (MSA2) has strips (ST) with a mark-to-space ratio of one-to-one and a centre-to-centre spacing λs2/2 chosen such that fo/fs2 is in the range 0.80 to 1.14 but excluding substantially 1.0, whereby a stopband in the amplitude-frequency response of the coupler (MSA2) between 2fs2 and 4fs2 suppresses the amplitude-frequency response of the input and output transducers (IP and OP) over a range of frequencies including 3fo ± 0.5fo.