High frequency scattering by a conducting ring

Asymptotic formulae are derived for the Fourier coefficients of the thin wire kernel in the integral equation for the electric current on an electrically large, thin circular loop. The total current induced on the ring by a plane electromagnetic wave is approximated by a modified physical optics term proportional to the incident field, plus resonant terms of lossy circulating waves. Numerical evaluation of the dominant poles and residues of the ring transfer function provides the amplitudes and complex propagation constants of these natural modes.