Analysis of slotted sectoral waveguide antenna arrays embedded in cylindrically stratified media

Abstract

Slotted waveguide antenna arrays with dielectric covers are widely used in both military and civil applications due to their low-profile, high power handling capacity, and the ability to conform to the host platform. Conformity is especially required for air platforms where aerodynamics and radar cross section (RCS) of the vehicle are of utmost importance. For an air platform, one or more dielectric layers (monolithic or sandwich radomes) can be used to protect the antenna from the extreme flight conditions. Although accurate and efficient design and analysis of low-profile conformal slotted waveguide arrays is of great interest, available solution methods in the literature usually suffer in terms of efficiency and memory requirements. Among the available solution methods, integral equation (IE) based ones that utilize the Method of Moments (MoM) are widely used. However, the IE solvers suffer from long matrix fill times, especially when cylindrically stratified media are considered. In this study, a slotted sectoral waveguide antenna, coaxially covered by multiple dielectric layers is analyzed with a hybrid MoM/Green’s function technique in the space domain. Only the fundamental mode of propagation (TE11) is assumed to be excited inside the sectoral waveguide. The longitudinal slots are on the broadside wall of the sectoral waveguide and are very thin in the transverse direction; therefore, only the TE modes are assumed to propagate. The solution domain is divided into two by using the equivalence theorem and fictitious magnetic current sources on the waveguide slots. Note that for the purposes of this study, the waveguide wall thickness is assumed to be zero. However, it can be incorporated into the problem by adding a third region which would be a sectoral cavity. The magnetic sources on the slots are expanded by piecewise sinusoid basis functions, and the continuity of the tangential magnetic fields across the iii iv slots is enforced to construct the integral equation. The integral equation is then converted into a matrix equation using Galerkin’s procedure. To compute the elements of the mutual admittance matrix, two Green’s function representations for the two solution regions are used. For the sectoral waveguide interior, the dyadic Green’s function components for a sectoral waveguide corresponding to longitudinal magnetic currents are rigorously derived. For the cylindrically stratified dielectric region, closed-form Green’s function representations for magnetic currents are developed, which are valid for all source and observation points, including the source region, where two magnetic current modes fully or partially overlap with each other. The proposed analysis method can be easily extended to include: slotted substrate integrated waveguides, slotted cavity antennas, and similar aperture type antennas embedded in cylindrically stratified media. Numerical results in the form of equivalent slot currents and far-zone radiation patterns for a generic slotted sectoral waveguide are presented, and compared to the results obtained from the commercially available full-wave electromagnetic solvers