Cavity-excited Huygens' metasurface antennas: near-unity aperture efficiency from arbitrarily-large apertures

摘要

One of the long-standing problems in antenna engineering is the realizationof highly-directive beams using low-profile devices. In this paper we provide asolution to this problem by means of Huygens' metasurfaces (HMSs), based on theequivalence principle. This principle states that a given excitation can betransformed to a desirable aperture field by inducing suitable electric andmagnetic surface currents. Building on this concept, we propose and demonstratecavity-excited HMS antennas, where the single-source cavity excitation isdesigned to optimize aperture illumination, while the HMS facilitates thecurrent distribution that ensures phase purity of aperture fields. The HMSbreaks the coupling between the excitation and radiation spectrum typical tostandard partially-reflecting surfaces, allowing tailoring of the apertureproperties to produce a desirable radiation pattern. As shown, a singlesemianalytical formalism can be followed to achieve control of a variety ofradiation features, such as the direction of the main beam or the side lobelevel, by proper modification of the HMS and the source position. Relying on acavity excitation, this can be achieved without incurring edge-taper losses andwithout any degradation of the aperture illumination for arbitrarily-largeapertures. With the recent demonstrations of Huygens' metasurfaces atmicrowave, terahertz, and optical frequencies, the proposed low-profile designmay find its use in a myriad of applications across the electromagneticspectrum, from highly-directive antennas to highly-efficient quantum-dotemitters, reaching near-unity aperture efficiencies.