This paper presents a reconfigurable metasurface that is able to dynamically and independently control the gain and propagation direction of the radiated field, with reduced biasing complexity and power consumption at a low profile. Moreover, the proposed metasurface is guided-wave fed thus leading to a compact tunable leaky-waveguide structure. Heretofore, reported reconfigurable metasurfaces have mainly demonstrated dynamic tailoring of free-space waves by redistributing their reflection or transmission phase profiles at a fixed amplitude. In contrast, we demonstrate dynamic transformation of a guided wave into an aperture field with controlled amplitude such that the gain and scan angle of the corresponding radiated field are dynamically and independently controlled. In particular, the aperture field is digitally synthesized by the proposed tunable Huygens’ metasurface whose local transmission coefficient is able to be dynamically tuned as two digital bits of $-|T_o|$ and $+|T_o|$, where $T_o$ represents a user-defined constant. This digital synthesis and the deliberate utilization of a nonbianisotropic type Huygens’ metasurface simplify biasing requirements, and make the proposed design more feasible. Through simulations and experiments, we show dynamic steering of a beam from $-{40}^{\circ }$ to $+{40}^{\circ }$, and two broadside radiations with different radiation gains at a fixed operating frequency of 5 GHz.

We propose a highly efficient (nearly lossless and impedance-matched) all-dielectric optical tensor impedance metasurface that mimics chiral effects at optical wavelengths. By cascading an array of rotated crossed silicon nanoblocks, we realize chiral optical tensor impedance metasurfaces that operate as circular polarization selective surfaces. Their efficiencies are maximized through a nonlinear numerical optimization process in which the tensor impedance metasurfaces are modeled via multi-conductor transmission line theory. From rigorous full-wave simulations that include all material losses, we show field transmission efficiencies of 94% for right- and left-handed circular polarization selective surfaces at 800 nm.

We propose a new family of impedance-matched chiral metasurfaces that offer arbitrary polarization control at two different frequencies. To this end, two main problems are addressed: (1) determination of the required surface impedances for a certain user-defined chiral functionality at two frequencies and (2) their physical realization at microwaves. The first milestone is achieved through a proposed synthesis method that combines a semi-analytical method and a nonlinear optimization technique. In particular, the impedances are computed such that the devised chiral metasurface is also impedance-matched to a terminating medium. The chiral metasurfaces are then physically realized at microwaves by cascading layers of rotated arrays of multiple concentric rectangular copper rings. We establish that these proposed unit cells offer distinct dual-resonances that can be arbitrarily and independently tuned for two orthogonal linear polarizations at each of the two operating frequencies. This allows simultaneous physical mapping of the required surface impedances at two frequencies. The versatility and generality of the proposed numerical and physical solutions are demonstrated through two design examples: A dual-band circular polarization selective surface (CPSS) and a dual-band polarization rotator (PR). The dual-band CPSS is further confirmed experimentally at 20 GHz and 30 GHz based on a free-space quasi-optical system.

We present the design and experimental demonstration of an impedance-matched circular-polarization-selective surface that also offers spin-selective phase modulations at microwave frequencies. We achieve this by leveraging the theory of Pancharatnam-Berry phase shift and cascading four tensor impedance layers, each comprising an array of crossed meander lines. These meander lines are precisely tuned and rotated to implement particular tensor surface impedance values to satisfy the impedance-matching condition for the transmitted right-handed circularly polarized field while inducing Pancharatnam-Berry phase shift for only the reflected left-handed circularly polarized field. We present a detailed numerical synthesis technique to obtain the required impedance values to satisfy the impedance-matching condition, and demonstrate spin-selective phase modulations based on Pancharatnam-Berry phase shifts. To verify the proposed idea, we experimentally demonstrate nearly reflectionless transmission of right-handed circular polarization at broadside and reflection of left-handed circular polarization at ${33}^{\circ }$ off broadside at 12 GHz. For this purpose, a free-space quasioptical setup and a near-field measurement system are used to measure the transmitted and reflected circularly polarized fields, respectively.

This letter presents a simple, yet effective method for dynamic beamforming that can be readily realized by integrating a tunable binary Huygens’ metasurface with a leaky-waveguide antenna. Heretofore, dynamic beamforming has been difficult to achieve owing to the challenges in attaining full 360 $^\circ$ of dynamic phase tunability, while also independently controlling the local aperture amplitudes from zero to unity. In contrast, the hereby proposed method only requires $\pm 90^\circ$ of dynamic phase tunability (with arbitrary transmission amplitudes), thereby significantly alleviating the stringent tuning requirements. In particular, the proposed method is obtained by leveraging the antenna-array and holography theories, and utilizing the idea of “ virtual ” electric line sources. Based on full-wave simulations, we demonstrate the versatility of the proposed method through the designs of a Huygens’-metasurface-assisted leaky-waveguide antenna that generates various complex far-field patterns such as sector beams and Dolph–Chebyshev patterns.