Matsushita Electric Industrial Co., Ltd.

Yukio Kashiwagi

Toshio Ishizaki

Tomoki Uwano

Yukihiko Ise

Yasuteru Asakawa

Hiroshi Fukushima

In a piezoelectric resonator having a piezoelectric bar formed in a substantial rectangular parallelopiped and electrodes formed on a pair of confronting surfaces of the piezoelectric bar for resonating in the length expander mode, the piezoelectric bar has at least a bevel portion extending the longitudinal direction. In a ladder filter having series and parallel piezoelectric resonators, the series piezoelectric resonator has the bevel portion to shift a frequency of a spurious response to that of the parallel piezoelectric resonator to suppress the spurious response. It is disclosed that a second piezoelectric resonator has a piezoelectric bar formed in a rectangular parallelopiped has a length L, a width W, and a thickness T wherein L&gt;W&gt;T; and electrodes formed on a pair of confronting surfaces defined by L and T. Another ladder filter includes the second piezoelectric resonator as the series resonator to decrease a capacitance between the electrodes to increase an amount of attenuation. In the second piezoelectric resonator, when W&lt;T and 0.42&lt;T/L&lt;2.5, a coupling factor is large.

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Takarazuka, Japan

Yukio Kashiwagi