Hybrid Quasi-Reflectionless Filter Based on EMSIW and Microstrip T-junction

A quasi-reflectionless filter based on EMSIW (eighth-mode substrate integrated waveguide) resonators and microstrip T-junction is introduced in this paper. The bandpass filtering (BPF) response of the EMSIW cavities is analyzed in the first part of this paper. In order to optimize the selectivity, two TZs (transmission zeros) are achieved by introducing the source-load coupling. In the second part, the response of the bandstop filter (BSF) constructed with the microstrip T-junction structure is analyzed. Based on the analysis above, a reflectionless bandpass filter formed by the two structures analyzed above is proposed. Finally, in order to verify the design approach, the filter is fabricated and measured. The measured result is basically consistent with the simulation results.