Shiyougo Inoue

A miniaturized 3 /spl times/ 3-mm SAW antenna duplexer for the US-PCS band with temperature-compensated LiTaO/sub 3//sapphire substrate

This paper describes a temperature-stable and miniaturized SAW antenna duplexer for the 1.9 GHz US-PCS band that uses a temperature-compensated 42/spl deg/ Y-X:LiTaO/sub 3//sapphire bonded substrate. In this duplexer, the temperature coefficient of frequency is reduced to half or two-thirds of that of a conventional LiTaO/sub 3/ substrate. Also, it is shown that our new duplexer has a smaller insertion loss and offers sufficient power durability. These improvements are mainly due to the characteristics of sapphire, such as its larger thermal conductivity and smaller dielectric constant. Furthermore, the performance of our SAW duplexer is compared with that of two kinds of BAW duplexers, which are competitive technologies. As a result, it is shown that our newly developed SAW duplexer offers equal or better performance in a smaller package. This implies that our SAW duplexer is the best and the smallest PCS duplexer.

Analysis and Suppression of Side Radiation in Leaky SAW Resonators

This paper discusses side acoustic radiation in leaky surface acoustic wave (LSAW) resonators on rotated Y-cut lithium tantalite substrates. The mechanism behind side radiation, which causes a large insertion loss, is analyzed by using the scalar potential theory. This analysis reveals that side radiation occurs when the guiding condition is not satisfied, and the LSAW most strongly radiates at the frequency in which the LSAW velocities in the grating and busbar regions approximately correspond to each other. Based on these results, we propose a narrow finger structure, which satisfies the guiding condition and drastically suppresses the side radiation. Experiments show that the resonance Q of the proposed structure drastically improves to over 1000 by suppressing the side radiation, which is three times higher than for a conventional structure. Applying the proposed resonators to the ladder-type SAW filters, ultra-low-loss and steep cutoff characteristics are achieved in the range of 800 MHz and 1.9 GHz.

Low-loss SAW filter on Li/sub 2/B/sub 4/O/sub 7/ using novel-shape apodized structure for 1 GHz RF-ID system

This paper describes the longitudinally-coupled double mode SAW (DMS) filter on 45 X-Z Li2B4O7 (LBO) substrate for the 1 GHz RF-ID system in Japan. Since LBO has a lower dielectric constant, the aperture of the IDT on LBO tends to be wider so that the input and output impedance correspond to 50 Ω. The higher order transverse modes existing in such a wide aperture cause ripple responses in the pass band. Generally, to suppress higher order transverse modes, IDTs are apodized. However, it appears that the conventional apodized structure generates a notch response in the pass band due to the longitudinal modes. We theoretically analyze this longitudinal modes response using the longitudinal mode separation technique and propose a novel-shape apodized structure, which we termed “wave-shape apodization.” This completely suppresses both the notch response due to the longitudinal modes and the higher order transverse modes. Applying this wave-shape apodization, we successfully develop a practical 953 MHz SAW filter for the RF-ID system.