Surface acoustic wave filters

摘要

Surface acoustic wave bandpass transversal filters, e.g. television intermediate frequency filters, comprising a + theta DEG rotated Y-cut X-propagating lithium niobate substrate with theta in the range from 121 DEG to 127 DEG , preferably 123 DEG to 125 DEG . For a suitable range of filter bandwidths (35 db bandwidth between 0.05 and 0.5) these substrates provide reduced degradation of the filter upper stopband predominantly due to indirect bulk shear waves in the frequency range from the passband up to the frequency where direct bulk longitudinal wave degradation becomes significant. This frequency range is 41.5 MHz to approximately 55 MHz for a U.K. system t.v. i.f. filter and is 60.25 MHz to approximately 90 MHz for a Japanese system t.v. i.f. filter.