Analytic Model of Coax-Fed Printed Metasurfaces and Analysis of Antenna Parameters

We present a model for waveguide-backed metasurface antennas fed by one or more coaxial ports and compute key antenna parameters using the model. The metasurface antenna consists of a coax-fed planar waveguide/cavity embedded with subwavelength-sized metamaterial radiators that convert energy from the guided mode into a radiated wave. Designing a metasurface requires tailoring the geometry of the individual metamaterial elements and arranging them over the aperture to achieve a desired radiation pattern—a typically cumbersome and time-consuming task when performed with full-wave solvers. In recent work, a coupled-dipole approach has been applied to modeling metasurfaces that significantly accelerates the design process by avoiding reliance on full-wave simulations or experimental trials. In this article, we extend the coupled-dipole model of a metasurface by including the analytic model of a coaxial port. Using the reaction and equivalent circuit model of a coaxial-to-waveguide transition, we also propose an efficient method to compute the input impedance of a metasurface, enabling the calculation of gain and efficiency. Close agreement between the proposed model and full-wave studies is demonstrated. The proposed method can find utility as an effective tool for the design and optimization of metasurfaces for applications including wireless communication systems, imaging, and wireless power transfer.