Analysis of three-conductor baluns using the static capacitance matrix

A coupled, three-conductor TEM network is analyzed in the distributed frequency domain using its static capacitance matrix. The results of the analysis are applied to three specific narrowband baluns used to connect a dipole antenna to its unbalanced coaxial feed line. Although all these structures are narrowband in terms of input impedance, the balun action is theoretically frequency independent. Extensive input impedance and reflection coefficient measurements have been made on the three balun types discussed. Agreement with theoretical predictions varied from good to moderate. In most cases the theoretical model provided good engineering insight, particularly into balun sensitivity to the cross-sectional dimensions of transmission lines. Junction discontinuities are not taken into account in the model, and this is thought to be the major cause of discrepancies.<>