Abstract: A small ladder-type electric filter for use in radio equipment or the like, includes a casing, a plurality of resonators having a small mechanical quality coefficient and a frequency constant, and a plurality of resonators having a large mechanical quality coefficient. The small mechanical quality coefficient resonators and the large mechanical quality coefficient resonators being combined in series-parallel to each other. The external size of the large mechanical quality coefficient resonators is substantially equal to the external size of the small mechanical quality coefficient resonators. A plurality of terminal plates hold the plurality of small and large mechanical quality coefficient resonators in the casing. Slits are selectively formed in side edges of each of the plurality of large mechanical quality coefficient resonators for adjusting the resonance frequency of the large mechanical quality coefficient resonators to a predetermined resonance frequency.

Abstract: A ladder-type piezoelectric filter having a plurality of piezoelectric resonator elements connected to a series branch and a plurality of piezoelectric resonator elements connected to a parallel branch wherein each of the series and parallel piezoelectric resonator elements positioned on the input and output terminal sides, respectively, has a Qm value larger than that of the remaining series and parallel piezoelectric resonator elements, thereby improving a group delay frequency characteristic while suppressing any increment of an insertion loss.

Abstract: A ladder-type piezoelectric filter comprising a series-parallel combination of piezoelectric ceramic resonators and a plurality of connector elements each disposed on each side of each resonator, wherein an insulating elastic member is inserted between each resonator and each connector element to provide an excellent impact resistance and group delay frequency characteristics.