Single-Ended-to-Balanced Power Divider With Extended Common-Mode Suppression and Its Application to Differential 2 x 4 Butler Matrices

A new type of wideband single-ended-to-balanced (SETB) power divider (PD) is presented. The design achieves high level and extended frequency range of common-mode (CM) suppression. Slotline-to-microstrip transitions are essential parts of the design, for the CM signals will be terminated in the slotline and thus will be rejected. Slotline resonators are used to provide multiple resonances which form a constant passband. The design is verified via experiments and excellent performance is obtained, including 27 dB of CM rejection and 25 dB of mode-conversion suppression levels with 200% fractional bandwidth (0- $2f_{o}$ ). Based on this property, a differential $2\times4$ Butler matrix (BM) is presented using two SETB PDs and a 90 degrees hybrid coupler. A differentially fed array, which is composed of four wideband linear-polarized elements and fed by the proposed differential BM, achieves a very low cross-polarization level due to the excellent CM suppression from the BM.