Stepped-Impedance Band-Pass Filters with Improved Selectivity
Rectangular waveguide stepped-impedance structures have been recently proposed to achieve band-pass filters with reduced sensitivity to fabrication tolerances and routing capabilities. In this paper, a novel method is presented to enhance their selectivity. The design technique preserves the advantages of the baseline filter while allowing the inclusion of transmission zeros in its band-pass frequency response. This is achieved by introducing λg/4-stubs in some of the filter sections following a modular design process which implies a quick redesign of the sections affected only. The inclusion of the transmission zeros does not alter the good in-band behavior of the original filter and the method avoids cumbersome optimization processes. The technique has been tested by designing a Ku-band filter with two transmission zeros, one on each side of the passband.