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

Abstract

This 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.