Current Distribution and Radiation Characteristics of Thin, PEC Loops and Rings

Abstract

The current flowing around the circumference of a loop is symmetric in mode number n in a closed loop, but asymmetric in an impedance loaded loop. In other words for symmetric current, the Fourier coefficients $I_{-n} = I_n$, while for asymmetric current, this is not the case. Characterising this asymmetry is a recent advance in the theory. We set up this study in symmetry in this chapter and give the analytical formulae for the radiation from a closed loop. The radiation patterns at the fundamental resonance radiates directly along the $\pm z$ axis; the second harmonic shows an expected quadrupole behaviour. “Small” loops are defined as those with circumference less than $0.10 \lambda$, for decidedly good reasons and the radiation patterns for such loops are strongly azimuthal.