The authors reported band-pass (BP)-type tunable filters composed of ultrawide band (17%) surface acoustic wave (SAW) resonators composed of grooved Cu electrodes on 4°YX-LiNbO3 and interdigital capacitors (IDCs) on the same LiNbO3 substrate. However, the frequency of the tunable filter did not shift continuously because the capacitance of the IDCs was fixed. This time, the tunable filter with the frequency tunable range of 6.1% shifting continuously was obtained for the first time by applying voltage to the variable capacitance diode. The authors discuss the mechanical quality factor (Q) of variable capacitors and characteristics of the tunable filters.
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Kadota et al. (2012) studied this question.