The differentiated on-surface poynting vector as a measure of radiation loss from wires

Abstract

This article explores use of the on-surface Poynting vector to investigate the power flow at the surface of various thin wires, excited as antennas or scatterers. By differentiating the axial Poynting vector at the wire's surface, the rate of change of power flow in the current and charge along a perfectly electrically conducting (PEC) wire can be determined. The idea being explored is to see if a change in axial power flow can reveal anything about possible power loss due to radiation. The results from the differentiated Poynting vector are normalized with those obtained from an approach developed by the author called FARS (far-field analysis of radiation sources). Two antenna-excitation models are investigated for a straight-wire dipole: the usual tangential E-field model, and a two-wire transmission-line feed. Comparison of FARS and the differentiated Poynting vector results for a 10-wavelength dipole shows them to agree to within 10% relative to end peaks in the distribution of spatial radiation, except in the vicinity of the antenna's feed point. Both also show that radiation occurs not only near the feed point and ends of the antenna, but is distributed along its length, being associated with maxima of the current standing wave. Results presented for antennas such as a bent-wire dipole, circular and square loops, and for a straight-wire scatterer demonstrated the effects of shape and excitation on the distributed radiation