Microstrip balanced filter and balun filter incorporating edge couplings and connected couplings based on artificial transmission lines

The balanced filter with quarter-wave resonators using both edge- and connected-coupling mechanisms is proposed in this study. Under differential-mode excitation, two types of coupled-resonator pairs constitute the odd-mode half-circuit filter. Among the two coupled pairs, the connected coupling is realized by artificial transmission line with compact size possessing lowpass response. As a result, the constructed balanced filter has relatively low insertion loss. Specifically, by appropriately terminating one of the ports of the balanced filter, a balun filter features wide differential-mode/common-mode stopbands, good passband CMRR, and simple structure.