Novel Planar Compact Coupled-Line Single-Ended-to-Balanced Power Divider

In this paper, a novel planar compact coupled-line circuit is proposed to design a single-ended-to-balanced power divider (PD) that can be used in numerous balanced circuits and systems. By using the matrix transformation between the mixed-mode (MM) scattering parameters and the single-ended scattering parameters, the constraint rules are deduced to realize the performance of equal power division with in-phase, good input (output) port matching, high isolation between two balanced outputs, high suppression of the common-mode (CM) noise, as well as the mode-conversion suppression between differential-mode signals and CM noise. Then, the closed-form design equations are derived using the even- and odd-mode analysis. Finally, a microstrip PD, which works at 1 GHz, is designed and fabricated. The measured (simulated) operating relative bandwidth is 37% (38%) from 0.76 (0.83 GHz) to 1.13 GHz (1.21 GHz). The consistency between the simulated and measured MM scattering parameters verifies the correctness of the design theory.