Compact and tunable microstrip tri-band bandstop filter incorporating open-stubs loaded stepped-impedance-resonator

This article proposes a compact microstrip tri-band bandstop filter (TBBSF) operating at 2.57, 4.62, and 7.92 GHz. The proposed design composed of open-stubs loaded in a meandered stepped-impedance-resonator (SIR). Three different open-stubs are loaded in a SIR, among which first open-stub is responsible for realizing the second resonance frequency, whereas additional two identical open-stubs are capable of tuning the third resonance frequency. This allows the possibility of individual tuning of the resonance frequencies by adjusting the electrical length of the respective resonators. Based on the design concept, an experimental circuit is designed and fabricated, offering a simple design methodology and a very compact circuit size of 0.08 λ_g × 0.08 λ_g, which is more than 15 % smaller than the previously reported literatures. The simulation results are verified from the measurement and are found in good agreement. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:815–818, 2017