High power in-line pseudoelliptic evanescent mode filter using series lumped capacitors

A compact in-line pseudoelliptic evanescent mode filter for high power and wide spectrum applications is presented in this paper. The filter employs series lumped capacitors between adjacent resonators. Such capacitors are properly combined with the series distributed inductance of the evanescent mode sections so as to provide independently controlled transmission zeros. The proposed approach does not require any inductive wire connections between resonators and preserves the wide spurious free stopband characteristic typical of conventional in-line all-pole evanescent mode filters. The experimental results, including temperature and power tests, of a sixth order 11% fractional bandwidth prototype designed at 1.8 GHz with two symmetrically placed transmission zeros are reported.