Modeling the radiation from cavity-backed antennas on prolate spheroids using a hybrid finite element-boundary integral method

Conformal antennas are increasingly being deployed on the surfaces of air and land vehicles. Quite often, the mounting surfaces are doubly curved. A characteristic property of these antennas is the curvature dependence of their input impedance, resonant frequency, and radiation pattern. In light of this, it is vital that conformal antenna models include surface curvature so that the effects of local surface geometry on their resonant behavior and radiation pattern can be predicted more precisely. This is especially important for a highly resonant antenna, such as the micostrip patch, due to its narrow bandwidth. In addition, advanced material antenna loadings are increasingly being used in practice. These factors motivate the development of a new approach to modeling the radiation from conformal antennas on convex, doubly curved platforms utilizing the hybrid finite element-boundary integral (FE-BI) method. The hybrid FE-BI method, which combines the finite element method with the method of moments, is extended to model convex, doubly curved platforms by means of a specially formulated asymptotic dyadic Green's function. This asymptotic Green's function, formulated within the context of the uniform theory of diffraction (UTD), incorporates the physics of interactions on the surface of an electrically large, perfect electrically conducting prolate spheroid and is highly amenable to numerical applications. The prolate spheroid is a canonical shape that is sufficiently general to model the curvature of a convex, doubly curved mounting platform. The FE-BI method is used to investigate the effect of curvature variation on the resonant input impedance of a cavity-backed slot and a cavity-backed patch antenna recessed in the surfaces of prolate spheroids of varying dimensions. The effect of curvature variation on the far field radiation pattern of a cavity-backed patch antenna recessed in the surfaces of prolate spheroids of varying dimensions is also investigated using this method. Measured input impedance data for a patch antenna mounted on a planar and a doubly curved surface also is presented.