Chebyshev quarter wavelength wideband bandstop filter based on dumbbell annular ring resonator

In this letter, a novel seventh order equal ripple wideband bandstop filter (BSF) is proposed and demonstrated. This device is based on dumbbell annular ring (DAR) resonators which introduces additional magnetic coupling with quarter wavelength open circuited stubs in the conventional 50-Ω transmission line. However, introducing this DAR resonators (DARRs) generate multiple transmission zeros which is responsible for wider stop band and can be determined from the S-plane. Moreover, the proposed BSF has selectivity up to 170 dB/GHz, rejection level is better than 50-dB, suppress reflection up to 12-dB in the pass band and fractional bandwidth 113.1%. Besides, the group delay is within 3 ns over the 80% of the stop band. The simulated frequency performances of the device from two different software's are in well agreement with the theoretical data.