A compact UWB ring resonator BPF with double notched bands

In this paper a new design of ring resonator bandpass filter (BPF) with enhanced out of band efficiency and double band notch operation for ultra-wideband (UWB) applications is designed. The employed multi-mode resonator (MMR) is excited by two cross-form coupled lines (CFCLs) at two sides to attain quadruplet-mode UWB BPF performance. Besides, the features of CFCLs are manipulated to stop the unwanted passband harmonics and extra resonances, leading to an enhanced in-band efficiency of the BPF. Also, the size of the microstrip BPF is reduced using the CFCLs. In addition, in the suggested BPF structure dual band notch property is created by coupling dual-mode stepped impedance resonator (DM-SIR) to the main ring resonator. In addition to the dual bad notch performance, the employed DM-SIR provides a higher degree of freedom for tuning the resonant frequencies.