Currently, mobile or smart phones with multibands and a cognitive radio system require a tunable filter with a wide tunable range to simplify their circuits. An ultrawide-band resonator is an important device to realize the tunable filter. The relative bandwidths (BWs) of 12 to 17% of previously reported surface acoustic wave (SAW) resonators are not sufficient to realize the tunable filter. This time, the authors studied an SH 0 mode plate wave in a LiNbO 3 plate. As a result, plate wave resonators with a large electro-mechanical coupling factor ( k 2 ) of 0.55 (55%), an ultrawide bandwidth of 29%, a high Q of 700, and a large impedance ratio of 98 dB between resonance ( f r ) and anti-resonance ( f a ) frequencies were realized for the first time using 27.5–30°YX-LiNbO 3 plates. Applying these resonators to a ladder-type tunable filter, a wide tunable range of 19% was obtained.
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Kadota et al. (2013) studied this question.
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