Toyoji Tabuchi

SAW integrated modules for 800-MHz cellular radio portable telephones with new frequency allocations

Several technologies are developed to achieve broader band surface-acoustic-wave (SAW) filters for portable telephones used in an 800-MHz wideband (25-MHz) cellular radio system. The design and realization of a transmitter final stage filter (high-power filter) and a prefilter (high-performance filter) are examined from initial specification to final device operation. An insertion loss of less than 2 dB and a rejection level of more than 20 dB are achieved for the final stage filter, and less than 5 dB and more than 50 dB, respectively, are achieved for the prefilter. Two integrated SAW modules, an antenna duplexer and a high-power amplifier, that include the above SAW filters and satisfy almost all requirements for wideband cellular radio have been developed. Their physical dimensions are the same as those of previously developed 20-MHz models. New SAW electrode materials (Al+Ni, Al+Cu+Ni) have also been investigated to improve the power-handling characteristics of the transmitter final stage filter.<<ETX>>

Miniaturized SAW devices for radio communication transceivers

Various applications of surface-acoustic-wave (SAW) technologies are investigated in which the use of SAW devices would result in reduced volume and weight for VHF/UHF radio communication transceivers. Attention is given to improved insertion loss and power requirements reported for SAW filters. In particular, by analyzing the loss mechanisms of a previously developed high-performance SAW filter for mobile telephones, a new extremely low-loss SAW filter (loss of as low as 1.2-2.0 dB at 600 MHz) has been developed. The results of fundamental experiments for a SAW antenna duplexer using this new SAW filter as the transmitter filter with a semicoaxial filter as the receiver filter at 800 MHz are presented. >

New high-performance and low-loss SAW filters used in ultra-wideband cellular radio systems

Several new technologies are reported for the design of high-performance and low-loss surface acoustic wave (SAW) filters used in ultra-wideband cellular radios. Among them, new configurations for wideband bandpass filters applicable as receiver filters have been developed. These configurations allow 3- or 4-dB insertion loss and sharp-cutoff frequency responses. New structures for wideband band-rejection filters applicable as transmitter final stage filters have also been developed. Their use results in loss as low as 1.4 dB as well as high-power characteristics. A SAW front-end module constructed with SAW filters, with a low-noise amplifier, and with a single balanced mixer is described.<<ETX>>

A wideband SAW resonator and its application to a VCO for mobile radio transceivers

A new wideband SAW resonator has been developed for SAW-VCOs used in mobile radio communication transceivers. The resonator is based on a repeated structure of pairs of electrically connected IDTs, which provides a high Q and a wide frequency bandwidth. An experimental SAW-VCO module measuring 8/spl times/8 mm/sup 2/ offers a frequency-variation bandwidth of about 20 MHz, a C/N of 75 dB, and an output power of 3-4 dBm at 900 MHz, satisfying the specifications for Japanese MCA and business-use radio transceivers. >

Investigation of new low-loss and high-power SAW filters for reverse-frequency-allocated cellular radios

Japanese cellular radios employ reverse frequency-allocations of the transmitter and receiver frequency bands. A rather narrowband surface acoustic wave (SAW) transmitter prefilter and a new type of SAW low-loss and high-power transmitter final stage filter-dual configurations to previously developed US cellular radio system filter-have been developed. The dual configurations provide the stopbands for the filter at the lower side of the pass bands, which is a requirement for reverse frequency-allocation systems. Design procedures, including those for the piezoelectric substrates and the experimental results obtained for the filters of 1.5 dB low insertion-loss and over 30 dB stop band rejection at 920 MHz, are also presented. In addition, the frequency characteristics of the SAW antenna duplexer module used in Japanese new common carrier (NCC) systems are discussed.<<ETX>>

Acoustically-induced migration of thin film electrodes in SAW-resonator-coupled filters

The aging characteristics of recently developed SAW-resonator-coupled filters are discussed. The rejection level of the filter was decreased by applying power. This result means that the Q-factor of the surface acoustic wave (SAW) resonator decreases with applied power. This change was studied by means of resistivity measurement and microscopic observation. It was found that the resistivity of the thin film increases by stress-induced migration. The decrease of rejection level and the decrease of the resonators Q-factor are explained by the measurement resistivity. Voids and hillocks were observed on thin-film electrodes. These observations also support the resistivity increase caused by stress-induced migration. It was seen that the formation of voids and hillocks induced the resistivity increase in thin-film electrodes. It is concluded that the cause of electrical characteristics change is the resistivity increase in the thin-film electrodes.<<ETX>>