Design of Ultra-Wideband Balun Using Coaxial Transmission Line

Ultra-wideband baluns have been proposed using coasial transmission line. The amplitude imbalance of the coasial balun is found to be within 0.9 dB to -0.3 dB, from 0.3- 2.7 GHz. Similarly, the phase imbalance ranges between 10^° and -7^° from 0.6-2.7 GHz. Due to the design technique of the balun, its response in the lower frequency region is found to be poor. In order to overcome this, a number of annular ferrite beads are used around the coaxial cable. These ferrite beads act as RF chokes, whose impact on the balun has been analyzed in this paper. The modified balun displays significant reduction in the amplitude imbalance (upto 16.5 dB) and phase imbalance (upto 82^°) in the VHF region. The results of both the baluns are also compared in terms of their mised-mode S-parameters.