Yasuyuki Ida

Tunable Filters Using Ultrawide-Band Surface Acoustic Wave Resonator Composed of Grooved Cu Electrode on LiNbO3

A leaky surface acoustic wave (LSAW) with a leaky component on a 0–15°YX-LiNbO3 substrate has a large electromechanical coupling factor. In order to change the LSAW to a Love wave without a leaky component, a high-density electrode with a low velocity such as a Au or Cu electrode is composed on the substrate. A SAW resonator with a Cu-electrode/15°YX-LiNbO3 structure has been reported to have a wide bandwidth of 12%. In this study, in order to obtain a SAW resonator with a wider bandwidth for application to tunable filters, the authors fabricated one-port resonators with a grooved Cu-electrode/4°YX-LiNbO3 structure. This resonator had a 1.3-fold wider bandwidth of 17% and 1.3-fold higher resonant and antiresonant frequencies than a conventional resonator composed of the same thick Cu-electrode on 4°YX-LiNbO3 fabricated for reference. Moreover, the authors proposed the application of this resonator to a tunable filter by using a circuit to modify a conventional band-pass filter composed of inductors and capacitors (LC) and a tunable filter with a ladder-type circuit. As a result, tunable filters having tunable ranges of 7 and 9% at the center frequency and 3 dB bandwidths of 3 and 5%, respectively, have been realized.

Band-Pass-Type Tunable Filter Using Surface Acoustic Wave Resonator Composed of Grooved Cu Electrodes on LiNbO3

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.

Ultra wide band resonator composed of grooved Cu-electrode on LiNbO 3 and its application to tunable filter

A leaky surface acoustic wave (LSAW) on 0–15°YX-LiNbO3 has a large electro-mecahnical coupling factor, but it has a leaky component. The LSAW changes to Love wave without its leaky component, by using a high density metal electrode with a low velocity such as Au and Cu on that substrate. It was reported that a resonator composed of a Cu-electrode/15°YX-LiNbO3 had wide bandwidth of 12%. This time, in order to obtain a resonator with a wider bandwidth, authors attempted to fabricate one-port resonators composed of a grooved Cu-electrode/4°YX-LiNbO3. As the result, this resonator had a wider bandwidth of 17% of 1.3 times and higher resonant and anti-resonant frequencies of 1.3 times than the resonator composed of a conventional type of same thick Cu-electrode on 4°YX-LiNbO3 for reference. Authors proposed to apply this resonator to a tunable filter. As the result, the tunable filter having tunable range of 7% in center frequency was realized.

High Q SAW resonator using upper-electrodes on grooved-electrodes in LiTaO 3

Al-electrodes on 36–48°YX-LiTaO<inf>3</inf> substrates have been widely used in surface acoustic wave (SAW) filters and SAW duplexers because of having an optimum electro-mechanical coupling factor, reflection coefficient and good Q-factor. In this paper, authors proposed and constructed a new SAW structure composed of upper Al-electrodes accumulated on lower grooved Cu-electrodes in the LiTaO<inf>3</inf> substrate, which has approximately same electro-mechanical coupling factor and reflection coefficient as the Al-electrodes (0.1λ)/36–48°YX-LiTaO<inf>3</inf> in order to realize high Q-factor. As the result, the SAW resonator having superior Q-factor was realized compared with that of Al-electrodes( 0.1λ)/42°YX-LiTaO<inf>3</inf> substrates.

Improvement of insertion loss of band pass tunable filter using SAW resonators and GaAs diode variable capacitors

Tunable filters with a wide band tunable range are required for mobile phones with multi-bands and cognitive radio systems to simplify their circuits. Previously, the authors prototyped a band pass tunable filter, which continuously changes frequency from 1734 to 1844 MHz (6.1%) using surface acoustic wave (SAW) resonators and Si diode variable capacitors (varicap). However, the insertion loss was large compared with calculated one because the Q factor of the Si diode varicap was as low as 1 at 1.8 GHz. In this study, the authors improved the insertion loss of the tunable filter using GaAs varicaps. Compared with the Si varicap, the GaAs varicap has a higher Q factor of about 41 at 1.8 GHz. The authors fabricated a tunable filter composed of two SAW resonators and the GaAs varicaps instead of the Si varicaps on a printed circuit board (PCB). As a result, the insertion loss was drastically improved by 12 dB at the maximum, and the frequency characteristic approached the calculated one. The tunable range was also improved from 6.1% to 6.8%.

Band Pass Type of Tunable Filters composed of Ultra Wide Band SAW Resonators by adjusting Capacitors connected SAW Resonators

Authors realized a one port surface acoustic wave (SAW) resonator composed of grooved-Cu- electrodes/4°Y-X· LiNbO3 with an ultra wide bandwidth of 17 %. This time, the authors fabricated band pass type tunable filters using the SAW resonators instead of inductances and 2 kind of capacitors of interdigital capacitors (IDCs) and Si-diode variable capacitors. As a the result, when the IDCs were used, the tunable filter with the frequency tunable range of 6.8 % has been obtained by using 3 kinds of LiNbO3 substrates having different capacitances of IDCs and the same designed SAW resonators. On the other hand, when the Si-diode variable capacitors were used, by applying the voltage of 1.2 V to 10 V to the Si variable capacitors (Toshiba JDV2S71E) in order to adjust the capacitance, a tunable filter with the frequency tunable range of 6.1% has been continuously obtained for the first time.