Analyses of a square ring resonator used for bandpass filter design with multispurious suppression

In this article, we proposed a method to analyze the voltages, currents, and imaginary impedances of the resonant modes in the square ring resonator by converting the square ring resonator to a guided wavelength transmission line.The impedance of the first four resonant modes of the ring resonator can be found and used as the coupling region for the bandpass response design with a high quality and multispurious suppression. A filter example using this concept was designed, fabricated, and measured. The filter composed of two square ring resonators and a half wavelength microstrip line showed a wide rejection bandwidth until four times the passband frequency. The simulated and measured results of the filter example were in a good agreement. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1089–1092, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26702