Compact iris-coupled evanescent-mode filter for spacecraft S-band data transmitters

A modified combline structure is presented to design a compact narrowband bandpass filter. The length of the resonator is reduced effectively by introducing inductive iris in the conventional capacitive-post loaded combline structure. Further, the insertion loss of the filter is improved significantly by adjusting the cavity dimensions. A prototype narrowband (<;1% fractional bandwidth) filter, operating at 2.28 GHz, is realized for spacecraft data transmitter application. For comparison purposes, the measured performances of both the conventional and present filters are presented. The insertion loss of the present filter is reduced greatly from 2.35 dB to 0.9 dB, but exhibiting almost same electrical performance, while the length is reduced by 40% and thereby having reduced weight and volume.