Passive Metasurface Antenna with Perfect Aperture Efficiency

A passive metasurface antenna with perfect aperture efficiency is presented. The metasurface consists of an inhomogeneous impedance sheet placed above a conductor-backed dielectric substrate. The metasurface antenna is fed by a line source placed within the substrate, which couples to the impedance sheet. The impedance sheet transforms the cylindrical wave of the line source into an aperture field with uniform amplitude and phase. Since the inhomogeneous impedance sheet is fully reactive and the aperture fields are uniform, the metasurface antenna has 100% aperture efficiency. The inhomogeneous impedance sheet is designed in three steps. First, an integral equation is constructed that relates the surface impedance to the desired total electric field along the aperture. The integral equation is solved via the Method of Moments to find the required impedance sheet. The resulting impedance is complex-valued since the metasurface reshapes the power density. Subsequently, an optimization strategy is used to remove the real part of the sheet impedance while still achieving the field transformation of the complex-valued sheet. The reactive sheet introduces surfaces by way of discontinuities, which shuttle power across the metasurface to reshape the power density profile. Finally, the inhomogeneous impedance sheet is realized through the patterning of a metallic cladding.