Design of a Substrate Integrated Half Mode Coaxial Cavity Filter with Multiple Transmission Zeros

This article presents a second order Substrate Integrated Coaxial Line (SICL) based bandpass filter operating at 28 GHz with multiple transmission zeros. SICL cavity comprising of a L-bend line confined between a pair of dielectrics and shorted at both ends is conceived here. A bandpass filter is devised by coupling a pair of half-mode cavities generated from the proposed SICL cavity. In the designed bandpass filter, the selectivity is improved by placing a pair of transmission zeros on each lower and upper side of the passband. Three resonators operating in the out of band response of the bandpass filter is proposed to suppress the first higher order mode. These embedded resonators are realized by metallic vias connecting to the top conducting plane through a grounded coplanar waveguide (GCPW) line from the disconnected middle layer of SICL. Positioning of the three additional transmission zeros as a function of their GCPW length is analyzed. The proposed low insertion loss SICL filters exhibit 14.21% & 11.64% 3-dB fractional bandwidth and a good out of the band performance with rejection level better than 20 dB in both below and above the passband. Utilization of compact size and electromagnetically robust filters designed in SICL technology provide notable front end millimeter-wave communication system.