Tomoya Komatsu

Tunable Radio-Frequency Filters Using Acoustic Wave Resonators and Variable Capacitors

In this paper, we describe possible configurations for tunable filters based on RF surface or bulk acoustic wave (SAW/BAW) technologies. The frequency tuning is made possible by variable capacitors (VCs) connected to SAW/BAW resonators in the ladder-type filter configuration. First, it is shown that the passband edges can be controlled by one VC connected to each resonator. Second, it is discussed that the width and location of a passband can be controlled flexibly by two VCs connected to each resonator both in parallel and in series. Finally, the SAW filters with the proposed configuration are fabricated on a Cu-grating/15°YX-LiNbO3 substrate structure, and the tuning capability is demonstrated.

Wideband tunable love wave filter using electrostatically-actuated MEMS variable capacitors integrated on lithium niobate

A tunable bandpass filters with low insertion loss, sharp cut-off characteristics, wide bandwidth and wide tunability is strongly expected for future reconfigurable and cognitive wireless systems. We have demonstrated a wideband tunable filter with the center frequency of 1.08 GHz by directly integrating Love wave resonators and electrostatically-actuated MEMS variable capacitors on a 15 ° Y LiNbO 3 wafer. The Love wave resonators have an extremely large electromechanical coupling coefficient (k2 ∼ 30 %), providing wide bandwidth and wide tuning range. We confirmed that the 3 dB bandwidth was tuned from 146 MHz to 130 MHz by applying 15 V to one of the MEMS variable capacitors.

Design of narrow bandwidth ladder-type filters with sharp transition bands using mutually connected resonator elements

This paper proposes a new design technique for a ladder-type filter to reduce the passband width without sacrificing the insertion loss, out-of-band rejection, and steepness of the transition bands. First, it is shown that 2 transmission zeros can be generated by connecting an additional resonator in either series or parallel arm of the ladder filter topology. This new filter topology can be designed systematically by the derived-m transformation. Second, it is demonstrated that the narrow bandwidth, sharp transition bands, and large out-of-band rejection are simultaneously realized by applying the present technique to specifically designed ladder-type filters. Finally, this technique is applied to the design of a SAW filter fabricated on the Cu-grating/15degYX-LiNbO3 structure.

Reduction of Transverse Surface Acoustic Wave Leakage in Resonator on Al/42° YX-LiTaO3 Substrate for High-Frequency Applications

In this paper, we propose a new structure for reducing the extent of transverse surface acoustic wave (SAW) leakage for the SAW resonator on a 42° YX-LiTaO3 substrate. Such leakage occurs from the interdigital region toward the busbar region in the SAW resonators. The new structure has a Ta2O5 film outside the interdigital region. This structure can make the SAW velocity in the busbar region lower than the velocity in the interdigital region. Therefore, the new structure could reduce the extent of leakage, and contribute to confine the SAW energy in the interdigital region. This structure was applied in SAW resonators and ladder-type SAW filters fabricated on a 42° YX-LiTaO3 substrate. The insertion loss could be improved by suppressing transverse SAW leakage. This technique could be applied to the fabrication of the filters and duplexers using leaky SAW on a 42° YX-LiTaO3 substrate, and the SAW devices could exhibit excellent performance.