A Simple Printed Compensated Balun for Enhanced Ultra-Wideband Performances

This letter presents a printed compensated balun of simple structure for enhanced ultra-wideband performances. The presented design stems from the generic compensated type of Marchand balun with an optimization on selected parameters for the bandwidth enhancement. A simple planar structure based on a 3-metal-layered PCB is proposed to realize the optimal design of the circuit scheme. The proposed balun design was implemented on a standard FR4 PCB and successfully verified with consistent simulation and measurement results. The presented balun achieves ultra wideband performances with a return loss better than 10 dB from 0.45 GHz to 6.85 GHz, a bandwidth ratio of 15:1. Over the entire bandwidth, the magnitude and phase imbalances are within 0.5 dB and 10 °, respectively. To the best of our knowledge, this work performs the largest bandwidth among the printed or planar baluns reported in the literature to date.