A novel reflector-filter using a SAW waveguide directional coupler

摘要

The SAW waveguide technique was used to form a novelnreflector-filter for the realization of compact IF filters in CDMAnhandsets. The reflector-filter design is an attractive technique tonobtain characteristics with steep skirts in a short device length,nbecause the SAW propagation path is folded and the frequency response isnsynthesized by utilizing both IDT and reflector responses. In thisnpaper, we propose a new reflector-filter structure using a SAW waveguidendirectional coupler. For the implementation of the proposednreflector-filter, the key technology is the design of SAW waveguides. Wenhave formed SAW waveguides using Al gratings loaded on the surface ofnthe substrate. The pitch of the Al gratings has been chosen unequal tonhalf the acoustical wavelength to avoid the occurrence of the gratingsnstopband at the filters passband position. Using the proposednreflector-filter structure, PCS-CDMA IF filters were fabricated onnquartz substrates. The filter exhibited an insertion loss of 8.5 dB, a 5ndB bandwidth of 1.45 MHz, and a rejection of more than 33 dB at thencenter frequency +/-1.25 MHz with the package size of 4.8×9.1 mmn2. i.e., half the size of a conventional transversal filternwas achieved using the proposed reflector-filter technique