Even–odd mode analysis for multiband bandpass filters having multiple resonators and its microstrip implementations

Abstract

ABSTRACTThis article presents even–odd mode impedance/admittance descriptions for dual‐mode multiband filters having independently controllable passbands formed by multiple resonators in different electrical lengths. Even–odd mode impedance models of dual‐mode ring resonators are used. Using these models, conventional equivalent admittance formulas are revised with a frequency dependent separation coefficient to obtain the desired in‐band return loss levels by keeping each passband from the effects of other passbands. As the proposed method can be applied for dual‐mode multiband filters, a dual‐mode dual‐band microstrip filter is designed, simulated, and fabricated. Designed filter has two dual‐mode resonators in different electrical lengths which are comprised by square loop resonators having narrow slits. Fabricated dual‐band filter has also been measured in a good agreement with the simulated results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2664–2667, 2014