Abstract: A method of fine-tuning a monolithic crystal filter (11) having a solid electrode (16) on one side of a crystal wafer (13) and a pair of split electrodes (12-1 and 12-2) on an opposite side of the wafer, to define a pair of resonators (19 and 21), involves short-circuiting one of the split electrodes to the solid electrode to produce a filter resonator coupling frequency wave form having first and second peaks (P.sub.A and P.sub.B), the positions of which correspond to upper and lower short circuit resonator resonant frequencies (F.sub.A and F.sub.B), respectively, of the filter. Additional electrode material then is plated on one or the other half of the solid electrode (16) to balance the wave form peaks (P.sub.A and P.sub.B), thus balancing the open circuit resonator resonant frequencies of the filter (11). Additional electrode material then is plated on the entire solid electrode to fine-tune the midband frequency (F.sub.M) of the filter (11) to a final desired value (F.sub. MF).

Abstract: A method of manufacturing a monolithic crystal filter, and particularly a filter having a high midband frequency (e.g., 20 MHz or above) and a wide resonator coupling (e.g., 4 KHz or above), involves the plating of additional electrode material onto a pair of base-plated split electrodes on one side of a crystal wafer to establish a desired coupling between resonators of the filter. Additional electrode material then is plated onto a base-plated solid electrode on the opposite side of the crystal wafer to establish a desired midband frequency of the filter. When the electrodes are plated in this sequence, the resonator coupling decreases substantially during the additional plating of the split electrodes, but remains essentially constant, within tolerance limits, during the plating of the solid electrode, whereby further adjustment of the coupling is not necessary.

Abstract: A band-pass filter comprising a plurality of coupled electromechanical filters is disclosed. Each electromechanical filter has a frequency pass-band centered about a fundamental frequency and a plurality of higher frequency pass-bands which are centered about overtones of the fundamental frequency. At least one of the electromechanical filters has a fundamental frequency that is different from the other filters and all the filters have a common overtone frequency. The band-pass filter will pass all frequencies falling within the band about the common overtone frequency, while all other frequencies will be suppressed.