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Abstract

A two-pole monolithic crystal filter is described that includes grounded strip electrodes between input and output electrodes. The grounded strip electrodes have a higher resonating frequency than the input and output electrodes and also provide increased acoustical coupling and lower inter-electrode capacitance between the input and output electrodes, while having little or no effect on the midband electrical characteristics of the filter. Because of the increased coupling, the input and output electrodes can be spaced further apart than heretofore possible in prior monolithic crystal filters. Moreover, further increases in the acoustical coupling can be achieved by arranging a plurality of strip electrodes between the input and output electrodes. The inventive monolithic crystal filter can be advantageously utilized for filtering the IF signal developed in the IF portion of an FM radio receiver.

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First Claim