Yasuhiro Kuratani

Ultra-wideband and high frequency resonators using shear horizontal type plate wave in LiNbO3 thin plate

A cognitive radio system requires a tunable filter with a wide tunable range to compose a simple front-end. Because the tunable range is limited by the bandwidth (BW) of resonators, an ultra-wideband resonator is an important device to implement the tunable filter. The authors previously obtained low frequency resonators with a wide BWs of 26 to 29% and a large impedance ratios of 92 to 98 dB between resonance (fr) and anti-resonance frequencies (fa) using 0-th mode shear horizontal (SH0 mode) plate wave in a LiNbO3 plate. Also, a tunable filter with the tunable range of 13% was demonstrated. However, the frequency (fr =1.8 MHz and fa = 2.3 MHz) is too low for modern wireless communication. Also, the resonators suffered from ripples due to transverse mode between fr and fa. In this study, high frequency SH0 mode plate wave resonators (fr = 430–560 MHz and fa = 530–670 MHz) with a wide bandwidth and a large impedance ratio have been fabricated using an ultrathin LiNbO3 plate. The ripples were suppressed by an apodized interdigital transducer.

Ultrawide band ladder filter using SH 0 plate wave in thin LiNbO 3 plate and its application

Currently, a cognitive radio using vacant frequency band of digital TV (DTV) channels (TV white space: 470 to 710 MHz in Japan) is receiving a lot of attention. The cognitive radio strongly requires a tunable filter covering a wide frequency range of DTV band and bandwidth tunability. Authors previously fabricated ultra-wide band 0-th mode shear horizontal (SH0) plate wave resonators for the DTV band. A T type ladder filter, which has a low minimum insertion loss and an ultra-wide bandwidth covering the DTV channels, was numerically synthesized from the measured characteristics of the resonators. Combining the wideband filter and a band rejection filter composed of several resonators with different frequency, the band pass filters with center frequencies of 530 and 660 MHz, which are corresponding with lowest and highest frequencies in DTV band, were obtained. This paper shows that the combination of the wideband filter and both type band rejection filters connected with variable capacitors enables a tunable filter with large tunable range of frequency and bandwidth, and a large rejection of the outside of DTV band.

High frequency resonators with wide bandwidth using SH 0 mode plate wave in thin LiNbO 3

Currently, an ultrawide band resonator used for a tunable filter with a wide tunable range is strongly required, because a mobile phone with multi-bands and a cognitive radio system require such a tunable filter to simplify their wirelss front-end circuits. The authors developed resonators with ultrawide bandwidths of 26% to 29% and large impedance ratios of 92 to 98 dB between resonance (fr) and anti-resonance frequencies (f_a) using a 0-th shear horizontal (SH₀) mode plate wave in a 28-30°YX-LiNbO₃ plate. However, the resonators were of low frequency as f_r = 1.8 MHz and f_a = 2.3 MHz and suffer from ripples due to transverse mode between f_r and f_a. In this study, high frequency SH₀ mode plate wave resonators (f_r = 440 ~ 560 MHz) with a wide bandwidth and a large impedance ratio and without ripples have been fabricated using an ultrathin LiNbO₃ plate and an apodized interdigital transducer.