Inline Waveguide Filter With Transmission Zeros Using a Modified-T-Shaped-Post Coupling Inverter

Abstract

This letter reports the design techniques for a class of inline waveguide bandpass filters with sharp-rejection capabilities at the lower stopband based on a novel nonlinear-frequencyvariant-coupling (NFVC) structure. The proposed NFVC consists of a modified-T-shaped metallic post (MTP) that is placed at the center of the waveguide broad wall with its open arms lying along the waveguide width. The engineered NFVC structure produces a first-order bandpass filtering transfer function with a pair of transmission zeros (TZs) located below the passband range. To demonstrate the usefulness of the proposed NFVC inverter, a 9.9-GHz third-order inline waveguide bandpass filter prototype with two TZs is developed and tested. It consists of two half-wavelength cavity resonators coupled together via the conceived MTP coupling structure. The measured results are in close agreement with the EM simulated ones, thus validating the devised waveguide filter design principle.Index Terms-3-D filter, bandpass filter, coupling-matrix synthesis, frequency-dependent coupling, inline filter, microwave filter, transmission zero (TZ), waveguide filter.

A Compact Wideband Waveguide Filtering Antenna with Transmission Zero

“…ing various compact waveguide filters with several TZs [12][13][14]. However, these proposed FVC networks have been utilized for the design of narrowband waveguide filters (BW < 10%).…”