Quantitative assessment of the operation of the infinite balun

We investigate the balancing efficacy of the "infinite" balun using a numerical simulation of a log periodic dipole antenna fed from a coaxial source via an infinite balun. The simulation enables the accurate representation of the coaxial source and the computation of the current on the two conductors of the feed transmission line. We show that the infinite balun feed arrangement results in localized current imbalance and storage of surface charge in the vicinity of feed point of the antenna. The result is not unexpected, but it is interesting to see the degree of current imbalance and how this imbalance diminishes with distance away from the feed point. It is shown that lengthening the portion of the feed transmission line in front of the foremost elements improves the current balance and therefore the co-polarized gain at the upper operating frequency of the antenna where these elements are active.