Compact H-plane dual-band bandstop waveguide filter

Abstract

This paper proposes a third-order miniaturized H-plane dual-band bandstop waveguide filter. Split ring resonators (SRRs), in the form of printed-circuit inserts, are used for the filter design. A simple and straightforward novel design algorithm for the waveguide SRR is introduced, which provides essential foundation for the development of the H-plane filter with multiple individually tunable stopbands. The third-order H-plane dual-band bandstop filter is implemented using SRRs for each stopband separated by quarter-wavelength waveguide sections to realize the immittance inverters for the corresponding center frequencies. Miniaturization of the filter is accomplished by the use of a properly designed insert within the waveguide section acting as the inverter. To demonstrate the usefulness of the proposed novel design algorithm and miniaturization concept, a compact H-plane dual-band bandstop waveguide filter is designed featuring independent control of the specified stopbands. The stopbands are located at center frequencies $$f_{01}=8.90\hbox { GHz}$$ and $$f_{02}=10.90\hbox { GHz}$$ and exhibit equal bandwidths of 340 MHz. The undesirable coupling between the SRRs for different stopbands on the insert is eliminated, along with their respective couplings to the additional insert for the inverter miniaturization. Thus, each of the stopbands is flexibly tuned by the adjustment of dimensions of the particular SRR. The proposed design using a shorter inverter preserves the characteristics of the conventional filter, while the improvement of the overall device in terms of compactness is 32%. The designed compact H-plane dual-band bandstop waveguide filter is experimentally validated, and the three-dimensional electromagnetic simulation and measurement results are in good agreement.