Dual-coupled monolithic crystal element for modifying response of filter

摘要

A dual-coupled monolithic crystal element is connected to a crystal filter to bypass signals of a predetermined frequency which are applied through the filter. The shunt connected crystal element can be used with a bandpass filter to bypass frequencies at which the crystal filter produces a spurious response so that such frequencies will not appear in the filter output. Alternatively, the monolithic element can be selected to bypass frequencies adjacent the edges of a band which is selected, to provide sharp attenuation at the edges of the band thereby providing a very steep filter characteristic. The monolithic element includes a flat quartz wafer with electrodes provided on both sides at two separate portions of the wafer to form two resonant portions coupled through the wafer. The electrodes of one portion are connected across the input or the output of the crystal filter, and both electrodes of the other resonating portions are grounded.