電極つい数重み付け法による携帯電話用SAWフィルタの開発

抄録

This paper describes a new weighting method for SAW filters to increase the out-of-band rejection level and its application. The present method is to weight the number of finger pairs in the interdigitated interdigital transducer (IIDT) which are composed of overlapping electrodes of the same length. To calculate the optimum weighting condition, the IIDT structure with two reflectors has been expressed by ten port network model based on equivalent circuit model developed by W. R. Smith. Using this method, we designed and fabricated 800 MHz bandpass filters for portable telephones. We mounted them in small leadless chip carriers which were 5mm× 5mm×1.6mm in size. The characteristics of frequency response was 3.5dB maximum insertion Itss in pass-band, 24 dB stop-band rejection, and 1.75 input-voltage standing wave ratio between -30°C and 70°C. We also designed and fabricated 1.5 GHz band SAW filters for a future cellular telephone system. An IDT pattern with 0.7μm line-and-space was deliniated by g-line projection type stepper.