A low loss CDMA-IF filter based on RSPUDT on LBO substrate

A high performance and novel SAW IF 210 MHz filter for CDMA (PCS) system is developed on LBO substrate. The filter consists of double-tracked filters which are connected in parallel on one chip. The main track-filter is RSPUDT filter having grating reflectors, and mainly performs low loss pass-band of the total filter. The sub-track filter consists of SPUDTs arranged either side of grating reflectors. It is set to be phase-inversion at the cutoff frequency region to improve the skirt slope of the main-track filter, but is suppressed at the pass-band to avoid degrading the insertion loss of main-track filter. The minimum insertion loss of 3.5 dB, the phase linearity of 3.3° rms and the stop band attenuation better than 35 dB are achieved successfully. The developed IF filter fits into small sized ceramic package (7.0×5.0×1.6 mm
³
) and has high performances of the frequency characteristics.