Limitations of the modified transmission line equations, a comparison with NEC

Abstract

We utilize both the NEC computer code and the transmission line models to compute the resonant frequencies, amplitudes and Q of the low order resonances (<6) of a transmission line illuminated by an electromagnetic wave. We find that the commonly used assumption that the transmission line equations are valid so long as the wavelength of the electromagnetic wave is much larger than the separation between the wires to be insufficient. In addition we find that unless the line is much longer than the separation between the wires, there can be major disagreements between the transmission line equations and Maxwell's equations. We find that in these cases the transmission line equations give resonant frequencies that are too high, field cable coupling that is too high and resonant Q's that are too high. The paper suggests some simple explanations in terms of re-radiation of energy and the electrical length of the transmission lines.