Extreme Beam-Forming With Impedance Metasurfaces Featuring Embedded Sources and Auxiliary Surface Wave Optimization

We present the end-to-end design of compact passive and lossless metasurface antennas with integrated feeds. The complete low-profile system consists of a single-layered reactive impedance metasurface on top of a grounded dielectric substrate, and is fed by sources which are embedded inside the substrate. The top impedance layer is implemented with an array of printed metallic wires, each of which is periodically loaded with subwavelength reactive elements (e.g. printed capacitors). An accurate and efficient volume-surface integral equation-based model of the device is developed, and used as the basis for the rapid optimization of the wire impedances, with the goal of producing the desired radiation characteristics. It is found that the optimized designs leverage tailored surface waves to facilitate the realization of extreme field transformations. In particular, we present surfaces capable of wide-angle beamforming up to 60 degrees off-broadside with nearly 100% aperture efficiency. We also demonstrate a multi-input, multi-output, antenna with two embedded sources emitting independent beams at +/- 20 degrees. The output beams each exhibits an aperture efficiency of around 90%, despite sharing the same physical aperture. Our design framework is supplemented by several feasibility-related constraints, which can significantly enhance the power efficiency as well as the bandwidth of the metasurface antennas when they are implemented in practice. Utilizing these constraints, a Chebyshev pattern antenna with a side lobe level of -20 dB is designed with realistic loaded wires and validated with full-wave simulations. The obtained radiation pattern confirms the ability of the developed framework for arbitrary beam-shaping. The realized power efficiency (limited by copper and dielectric losses) is over 93% and the 3-dB directivity bandwidth slightly over 6%.