A Novel Balanced-to-Unbalanced Diplexer Based on Four-Port Balanced-to-Balanced Bandpass Filter

In this work, a novel balanced-to-unbalanced (balun) diplexer is presented. By properly converting symmetric four-port balanced-to-balanced bandpass filter to a three-port device, a balun bandpass filter with high selectivity and extended stopband can be realized. Based on such a well-designed balun bandpass filter, a balun diplexer can be accomplished by combining two balun bandpass filter with two 50 matching lines. For demonstration, two fourth-order balun bandpass filters centered at 1.2 GHz and 1 GHz are employed to design and fabricate the balun diplexer. Specifically, the fabricated balun diplexer has the merits of compact size, wide stopbands, high isolation, and good common-mode rejection ratio.