Balanced and Unbalanced Duplexers Using Common Oval Dielectric Resonators

In this paper, dual-mode oval dielectric resonator (DR) is proposed as common resonator to realize all four kinds of balanced and unbalanced duplexers. The conventional topology is replaced with the novel one of sharing input and output dual-mode resonators at the same time for miniaturization. By adjusting the aspect ratio and height of the oval DR, the two modes are separated properly to form two channels of duplexers. After locating probes delicately according to the orthogonality of dual-mode fields, the channel transmission and isolation are ensured simultaneously under sharing output DR. Moreover, both dual-mode unbalanced and balanced operations are studied to extend the topology to all four kinds of duplexers. For verification, balanced-to-unbalanced (B-U) and balanced-to-balanced (B-B) duplexers are both fabricated and tested. Low insertion losses better than 0.59 dB are achieved in both two designs. High isolations lower than -36 dB and -50 dB and common-mode rejections lower than -44 dB and -52 dB are observed in the B-U and B-B duplexers, respectively. The exhibited high performance with reduced resonators demonstrates the potentials of the proposed duplexers in miniaturized FDD communication systems for connecting balanced/unbalanced transceivers with balanced/unbalanced antennas.