A dual-band bandpass filter using open-loop resonator

This paper presents a way of dual-band bandpass microstrip filter design based on open-loop resonator. The asymmetric structure gets better out-of-band rejection comparing to the symmetric structure for the two open-loop ring resonators. This paper also discusses the transmission characteristics of asymmetric two open-loop ring resonators varys with the feed lines position, the coupling spacing and the width of the loop line. Then, based on this foundation, four plane cascaded couple open-loop resonator are used to design a dualband bandpass filter with low insert loss and high image-rejection for dual-band Wimax receiver application.