RSPUDT filters based on different width split fingers

RSPUDT filters based on different width split fingers for IF applications have been developed. Such filters provide improvement of insertion loss comparing to DART-RSPUDT filters. A new optimization procedure for RSPUDT filter design has been proposed based on the adjustment of RSPUDT through a synthesis grid of narrow structure elements. The width of these elements is equal to or smaller than a minimal finger width of a basic SPUDT structure. This approach provides additional improvement of filter characteristics. DWSF-RSPUDT filters on quartz and 112°-LiTaO₃ are reported. Relative bandwidths of these filters are 1-3% and out-of-band rejection about 40 dB. Insertion loss is 1-3 dB better than that for equivalent filters based on other RSPUDT structures.