A Novel Unbalanced‐to‐Balanced Diplexer With High Isolation and Wide Stopband

ABSTRACT A novel unbalanced‐to‐balanced diplexer with high isolation and wide stopband characteristics is proposed. It uses a dual‐mode resonator as the common resonator, coupled with uniform impedance resonators and step impedance resonators at different center frequencies to form the lower and higher bands of the diplexer. Transmission zero introduced by the dual‐mode resonator effectively improves frequency selectivity, thus improving isolation. At the same time, a wide stopband is achieved by separating the spurious harmonics of the three resonators from each other. To verify the feasibility, a diplexer with center frequencies of 1.58 GHz and 2.46 GHz was fabricated, with in‐band differential‐mode isolation of 50 dB and 48 dB, respectively. Better than 20 dB stopband rejection up to 17 GHz.