Planar Low-Loss Ultra-Wideband Coaxial-Less Balun and 4-Way Combiner for High-Power Applications

This paper presents a planar high-power low-loss ultra-wideband balun and its application in the design of a 4-way combiner. The balun is based on a ferrite core and PCB transmission lines. Its coaxial-less design offers a PFAS-free alternative, enhanced flexibility due to unrestricted characteristic impedances, as well as improved repeatability and cost-efficiency by minimizing assembly steps. The paper details the balun’s analysis, simulation, and implementation, supported by experimental validation. Across the 20 to 835 MHz frequency range, the balun achieves a return loss and insertion loss better than 22.4 dB and 0.5 dB, respectively, with amplitude and phase imbalances less than 0.7 dB and 10°, respectively. Additionally, the paper demonstrates a 4-way combiner based on the proposed balun. The combiner achieves measured RL and IL values better than 17.5 dB and 0.5 dB, respectively, within the 20 to 500 MHz frequency range, while handling over 400 W of pulsed power.