Analysis and synthesis of two step coupled gap resonator and its application as a bandpass filter

In this manuscript, a two step gap coupled resonator is modelled for designing a bandpass filter. The proposed structure is viewed simultaneously as edge coupled section and parallel coupled section. A detailed nodal analysis of the proposed coupled gap sections using different current and voltage equations are described, which is further derived to obtain different admittance parameter equations. Finally comparing those equations with normal two port network, even and odd mode impedance difference (Z0o-Z0e) equations are obtained in terms of parallel coupled admittance inverter (Jg1) and shunt susceptance (Bg1) at the edge coupled section. This equation is further used for designing the resonator with bandaccepted characteristics. A three pole wideband bandpass filter is demonstrated by series arrangement of four such coupled resonator unit. The proposed bandpass filter exhibits FBW of 53.5%. All the results are well verified by numerical simulation and validated through experiments.