A Coupled-Line Balanced-to-Single-Ended Out-of-Phase Power Divider With Enhanced Bandwidth

In this paper, a coupled-line balanced-to-single-ended out-of-phase power divider is proposed. Configured by three quarter-wavelength coupled lines, the proposed power divider is compact and able to enhance the bandwidth of differential-mode power dividing, isolation, common-mode suppression, and phase difference between the output ports. Furthermore, enhancing the bandwidth for common-mode suppression using additional quarter-wavelength open stubs is discussed. Analytical solution of the parameters for specified bandwidth can be achieved using oddand even-mode analysis. Analytical and practical bandwidth limitation has been analyzed, and it is shown that the bandwidths can be controlled by the oddand even-mode impedance of the coupled lines. For demonstration, a prototype of size 15 mm x 95 mm (0.15 λgx0.95 λg) achieves an operating bandwidth (|SddAA| <; -20 dB) of 30% with the minimum insertion loss of 0.1 dB.