A wideband and high isolation balun based on the ridge waveguide

This paper proposes a wideband and high isolation balun that mainly covers both the X and Ku bands based on the ridge waveguide. First, the design of the E-plane ridge waveguide power divider introduces equivalent amplitude and phase inversion between the two output ports along with high isolation, while realizing a wideband due to the characteristics of the ridge waveguide. Second, to facilitate the measurement and application, structures transitioning from single-ridge and dual-ridge waveguides to coaxial connectors are designed, respectively. Finally, by designing a cylindrical matching structure for the E-plane ridge waveguide power divider and terminating it with a 50 Ω matching load, the return loss and isolation performance between the two output ports of the balun are effectively improved. The proposed balun combines the wideband advantages of ridge waveguides with the four-port network characteristics, achieving the benefits of wide bandwidth, high isolation, and matching across all ports. The proposed balun is fabricated and measured, and the measurement results are consistent with the simulation results. The balun centered at 13.25 GHz has a 3 dB fractional bandwidth of 78.65% (8.1–18.6 GHz). The measured return loss of the balun is better than 10 dB, and the isolation between the output ports is better than 12 dB. Compared with the conventional balun, the balun in this paper operates with a wide bandwidth, high isolation, and better matching performance of each port.