On the Electromagnetic Fields Excited in a Finite-Length Circular Cylindrical Cavity by Plane Wave Incidence on a Longitudinal Aperture

A semianalytical solution for the electromagnetic fields produced in a finite-length circular cylindrical cavity by plane wave excitation of a thin longitudinal aperture is provided. A perturbative approach is applied in which internal fields are computed using a perturbed perfectly conducting cylindrical cavity dyadic Green's function applied to a magnetic current source representing the aperture fields. This magnetic source is approximated as equal to the magnetic current in a thin aperture of the same length within an infinite planar ground plane under plane wave excitation, and is determined from a numerical solution of the complementary problem (i.e., a finite-length thin PEC strip) that is independent of the cylinder radius and length. The resulting fields inside the cavity are expressed as a summation of the discrete transverse electric TE $^{z}$ modes of a perfectly conducting cylindrical cavity. The perturbative correction to Green's function accounts for power losses in the cavity walls and through the aperture, with the reciprocity theorem applied to estimate the latter. Predictions from this approximate method are compared with fully numerical simulations using the method of moments, and found to show reasonable agreement in situations for which the assumptions used should be applicable. Additional results are illustrated as cylinder and aperture properties are varied to demonstrate the utility and efficiency of the method.