Yasuhide Iwamoto

High-frequency SAW duplexer with low-loss and steep cut-off characteristics

In CDMA (code division multiple access), analog, and partly TDMA (time division multiple access) cellular phone systems, transmitting and receiving are carried out simultaneously. Thus, an antenna duplexer is needed. An antenna duplexer using ladder-type SAW filters was first applied in an AMPS (Advanced Mobile Phone System)-CDMA system in 1998. The package size was 9.5 /spl times/ 7.5 /spl times/ 2 mm. The development of SAW antenna duplexers will require SAW filter designs that enable lower loss and a sharper cut-off, electrode materials that provide higher power durability, and package designs that enable lower loss and a smaller size. The miniaturization of this duplexer has been achieved by improving the filter chip and reducing the package size to 5 mm square. However, SAW duplexer with low-loss and steep cut-off characteristics is needed for high frequency applications. Through improved SAW filter characteristics, a duplexer for a 1.9 GHz PCS (personal communication services)-CDMA system has been realized. This paper describes these advanced technologies.

1.9 GHz range ultra-low-loss and steep cut-off double mode SAW filter for the Rx band in the PCS antenna duplexer

This paper describes the DMS (double mode SAW) filter design techniques to achieve the ultra-low-loss and steep cut-off characteristics required for the Rx filter in the PCS (personal communications service) duplexer. It is the first attempt to employ DMS filters for antenna duplexers in mobile phones. It is demonstrated that the common ground inductance L/sub g/ and the coupling capacitance C/sub c/ between the input and output terminals of the DMS filters dramatically enhances the skirt steepness and the attenuation for the lower frequency side of the pass band. Based on this result, we propose a novel DMS filter structure that easily controls the L/sub g/ and C/sub c/ values. Moreover, we propose a compact DMS filter structure connected in parallel, which reduces the insertion loss. Applying these technologies to the Rx filter, we develop a DMS-employing PCS antenna duplexer.

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.

Extremely low-loss SAW filter and its application to antenna duplexer for the 1.9 GHz PCS full-band

An antenna duplexer for the 1.9 GHz PCS-band handsets is realized by developing extremely low-loss and ultra-steep cut-off SAW filters. In this paper, design techniques to achieve the characteristics that satisfy all severe specifications required for the PCS-band duplexer is presented. Developed SAW duplexers have the insertion loss of -2.0 dB and -3.2 dB in the Tx and Rx band, respectively. Also, the attenuation levels are -53 dB and -45 dB. The device size is as small as 5/spl times/5/spl times/1.5 mm/sup 3/. These performances are sufficient for the PCS duplexer to be practical.