SURFACE ACOUSTIC WAVE FILTERS

摘要

PHB.32.727 23 Surface acoustic wave bandpass transversal filters, e.g. television intermediate frequency filters, comprising a +.THETA..degree. rotated Y-cut X-propagating lithium niobate substrate with .THETA. in the range 121.degree. to 127.degree., preferably 123.degree. to 125.degree.. 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 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 60.25 MHz to approximately 90 MHz for a Japanese system t.v. i.f. filter.