A novel SAW filter for IF-filtering in DECT systems

We have developed an improved SAW filter for IF-filtering in DECT systems. The filter is a two track reflector filter using EWC-SPUDTs as in- and output-IDTs and reflectors in the center of each track The propagation path of the SAW is folded in order to make better use of the total chip length. A similar configuration with identical reflectors in the tracks is known in literature, however, we used different reflectors in the tracks and this way we could improve the filter performance and especially the stop band attenuation considerably. The SPUDTs are withdrawal weighted, for the reflector design we used an electrode width weighting technique. The filter fits into a very small QCC10 package (9.1×7.1×1.8 mm³) and has high performance so that it can be used in a DECT base-station, too. The substrate is LiTaO ₃, X112.2Y, the center frequency is 110.59 MHz, the minimum IL is 8 dB typically, the 3-dB-bandwidth is 1.1 MHz and the stopband attenuation is better than 40 dB