Discussion of the Axial Ratio of a Square Loop Antenna with an Attenuating Current

The quality of the radiation field from a square loop antenna is evaluated using ARz, the axial ratio on the z-axis normal to the loop plane. For this evaluation, a generalized antenna model is used, where the current on a loop that is one guided wavelength in length is assumed to travel only in the forward direction, without backward currents. Firstly, the radiation field is formulated for the situation where the traveling wave current decays with attenuation constant $\alpha$ . It is found that ARz exponentially degrades as $\alpha$ increases. Secondly, a reactive current of weight q is superimposed onto the original current used for the first derivation. It is revealed that the degraded ARz is remarkably improved by the superimposed current. Throughout this discussion the difference in the axial ratios of the square and round loop antenna models is clarified.