Mixed-Mode Magic-Ts and Their Applications on the Designs of Dual-Band Balanced Out-of-Phase Filtering Power Dividers

In this article, two types of mixed-mode magic-Ts are proposed, which can realize out-of-/in-phase equal power divisions of multiple mixed modes ports with high isolation, common-mode (CM) rejection, and compact size. The first one, which has five ports, consists of a microstrip T-junction as a single-ended-to-single-ended (SETSE) in-phase power division network, and a microstrip/slotline transition as a balanced-to-single-ended (BTSE) out-of-phase power division network. Through the analysis of scattering matrix, a high isolation is obtained in the mixed-mode magic-T. The second one, which consists of a single-ended-to-balanced (SETB) in-phase power division network based on a microstrip T-junction, and a balanced-to-balanced (BTB) out-of-phase power division network based on a slotline T-junction. Taking advantage of the two types of mixed-mode magic-Ts, a BTSE filtering power divider (FPD) and a BTB FPD are investigated, respectively. The characteristics of the mixed-mode magic-Ts make the proposed configurations unique, since most published balanced FPDs based on complex multi-layer structures to achieve miniaturization. The proposed FPDs are integrated with a pair of asymmetric shorted-stub-loaded resonators (ASSLRs). The expected frequencies and bandwidths of the two differential-mode (DM) passbands can be obtained by turning the parameters of ASSLRs. Meanwhile, multiple transmission zeros (TZs) can be generated to improve the passbands selectivity by employing multiple coupling paths. Besides, a high and broadband CM rejection can be generated by introducing U-type balanced port, which simplifies the design process considerably.