Diffracted Microwave Fields Near Dielectric Shells: Computation, Measurement, and Decomposition

Abstract

This paper describes the fields produced near finite dielectric slabs and cones by incident, plane electromagnetic waves. It presents calculated and measured fields and their decomposition into constituent waves. The purpose was to understand approximations in some methods for analyzing performance of pointed, dielectric radomes. These methods compute patterns of an enclosed aperture antenna by evaluating diffraction integrals that have T(P), the complex-valued transmittance for externally incident plane waves as a factor in the integrand, where P is a point in the radome-bounded region. T(P) depends on polarization because of curvature and large incidence angles. Overall, radome analysis accuracy also depends on antenna and radome dimensions and on their proximity. For radomes with diameters exceeding 10 wavelengths (?), accuracy was good if T(P) had the value for an infinite flat sheet tangent to the surface at the intersection of an incident ray directly to P.¹ This direct ray method failed for radomes with diameters approximately 5? . ² Accuracy was high when T(P) was evaluated by integrating over a portion of the incident wave surface. Neither method accurately predicted fields very near thin radomes.