Dual-Mode Dual-Band DR Balun Filter Using Suspended Stripline Feeding Structure

This letter presents a novel dual-band balun filter based on dielectric resonators (DRs) fed by a suspended stripline (SSL) structure. By using the SSL feeding structure and the coupling slots, both the external couplings and the internal couplings of the two modes could be independently controlled at the same time. Thus, the bandwidths of two passbands are flexibly controlled. The principle of differential outputs is also analyzed. For demonstration, the dual-band balun filter centered at 3.93 and 4.14 GHz is fabricated and measured. From the measured results, low insertion loss, good amplitude, and phase imbalances are realized by the proposed balun filter.