The Performance of Balancing Networks Derived from the Shunt-Series, Equal-Delay Hybrid

Abstract

Both voltage and current baluns can be derived from the shunt-series equal-delay hybrid, but the voltage balun is superior to the current balun in applications such as broadband dipole antennas. To understand the lack of performance of the current balun it is necessary to distinguish between balance and symmetry. Both the voltage and current baluns exhibit the appropriate balancing behavior as is shown here. However, the current balun lacks symmetry when driving high impedances. This is shown through measurements and simulations of a representative shunt-series equal delay hybrid configured as both balun types. A 1.4-m biconical antenna exhibits a high input impedance well below its fundamental series resonance. For this reason the voltage balun topology provides better symmetry than does the current balun with such biconical antennas. The asymmetry manifests itself in vertical polarization measurements and is demonstrated here with a vertical polarization inversion test using two 1.4-m biconical antennas.