多対IDTを用いた2端子対弾性表面波共振器

抄録

Recently, many studies have been made of surface acoustic wave (SAW) resonators. Various configurations for them have been proposed. In previous papers, the authors have proposed a one-port SAW resonator composed of a long interdigital transducer (IDT) which has a large number of electrodes, and reported the realization of narrow band filters employing it. In this paper, a two-port SAW resonator using long IDT's is described. It is shown experimentally that narrow band-pass filters with low loss and a loaded Q of several thousand can be constructed monolithically employing two-port SAW resonators using long IDT's. The basic structure of the two-port SAW resonator is shown in Fig. 1. A theoretical consideration in chapter 2 indicates that two long IDT's positioned as shown in Fig. 1 constitute a two-port resonator by themselves. Typical measured frequency responses of the two-port resonators on ST-quartz with aluminum electrodes are shown in Figs. 3, 9 and 13. Steep peaks in each Fig. represent the resonances of the resonators. The minimum insertion loss in each Fig. is 2. 9-4 dB, with a loaded Q of 1, 800-3, 000. Grating reflectors made with aluminum strips were placed outside the two-port resonators whose frequency responses are shown in Figs. 9 and 13 to improve the insertion loss or Q. Figs. 12 and 14 show the frequency responses of the resonators with grating reflectors. Some improvement in the insertion loss and Q is seen from Figs. 12 and 14 compared with Figs. 9 and 13. The two-port resonator with grating reflectors whose frequency responses are shown in Figs. 12 were cascaded electrically to obtain a large out of band rejection. Figs. 15 shows the frequency response of the two-cascaded resonators. The minimum insertion loss is 6 dB at 156. 985 MHz, with a 3-dB width of 45 kHz, a loaded Q of 3, 500, a 40-dB width of 0. 21 MHz, and an out of band rejection of more than 70 dB over 0-200 MHz range.