Minseok Kim

This paper presents a design framework for synthesizing angularly selective spatial filters using non-uniform metagratings. While traditional metagratings focus on channeling energy into higher-order Floquet modes for a fixed incidence angle, we leverage the fundamental mode as a versatile degree of freedom to engineer spatial dispersion over a continuous angular spectrum. By strategically distributing non-uniformly loaded metallic wires and rigorously modeling their mutual interactions through an impedance-matrix formulation, we realize prescribed angular transfer functions with high efficiency. In particular, the framework is validated at 3.5 GHz through full-wave simulations of (i) low-pass, (ii) high-pass, and (iii) all-pass spatial filters. The results demonstrate that fundamental-mode engineering in non-uniform metagratins offers a highly efficient platform for advanced spatial wave manipulation.

This work presents a non-local terahertz metasurface integrated into a leaky-wave antenna for robust, wide-angle beam steering. The metasurface encodes a holographic pattern by explicitly inducing tangential and normal susceptibilities, along with magnetoelectric coupling. This design maintains stable radiation performance even when the longitudinal wavenumber of the incident guided mode - and thus its effective impinging angle - varies as a function of frequency. In particular, we show that there exists a limit to achieving exact angular insensitivity and propose an optimization-based framework to obtain the required susceptibilities that closely approximate near angle-insensitive performance for stable beam-steering performance. Additionally, an iterative synthesis approach is introduced that maps abstract susceptibilities to physically realizable structures. Full-wave simulations demonstrate a beam-scanning range of nearly 50 degrees over the 2.0-2.7 THz band - a more than threefold improvement over conventional local-metasurface designs.

This paper introduces a nonlocal, dual-band reconfigurable intelligent surface (RIS) designed for full-space beam synthesis at 4.0 GHz and 6.3 GHz. The constituent unit cells comprise a pair of interleaved sub-cells that are specifically engineered to operate independently at their respective target frequencies. This hardware-level decoupling facilitates an efficient synthesis framework based on microwave network theory (MNT) that rigorously accounts for mutual coupling within both bands. Under this framework, the optimal biasing for sub-cells is determined to achieve precise full-space beam synthesis at both frequencies. The proposed method is numerically and experimentally validated with an RIS comprising 14 X 14 varactor-loaded unit cells that can be individually biased. We experimentally demonstrate arbitrary beam profile synthesis beyond simple beam steering, including dual-beam and sector patterns in full space. Experimental and simulation results show good agreement with the MNT model, confirming the effectiveness of the proposed method.

We present a simple yet effective method for realizing compact waveguides that support efficient below-cutoff propagation with user-defined modal characteristics. The design incorporates a Huygens’ metasurface (HMS) as one of the waveguide walls, engineered to transform a cutoff mode into a propagating one by satisfying suitable boundary conditions. By tuning the metasurface’s local electric and magnetic responses, the propagation constant can also be independently controlled. We validate this concept both numerically and experimentally around 4 GHz in a waveguide of height 15 mm, well below the 10-GHz cutoff of a conventional counterpart, and show that it supports user-defined phase constants.

A surface-wave-assisted, dual-band, circularly polarized reconfigurable intelligent surface is proposed that allows arbitrary beam-shaping capability within the [4.35 GHz–4.5 GHz] and [11.8 GHz–12.3 GHz] frequency bands. In particular, alongside the proposed physical design of the surface, a genetic algorithm-based design framework is introduced to enable the synthesis of complex radiation patterns beyond simple beam steering. It is shown that the phase profiles obtained from the proposed optimization scheme naturally lead to the excitation of surface waves, which facilitate arbitrary beam shaping by satisfying the local power conservation condition between the normally impinging and arbitrarily reflected waves. To physically construct the proposed surface, cascaded symmetric unit cells are employed to facilitate circular polarization operation and realize dual-band operation. Furthermore, varactor diodes are incorporated into the design of unit cells so that the reflection phase can be independently and continuously tuned across the two frequency bands, with a tuning range of 300 degrees. The versatility of the proposed surface is demonstrated through design examples that achieve (i) unidirectional beam steering, (ii) multi-directional beam steering, and (iii) sector-beam formation within each frequency band.

We hereby propose a dual-polarized beam-deflecting metasurface that can double the scan-angle range of a phased-array antenna without compromising the directivity across all scan angles, including broadside. In particular, our research focuses on expanding the scanning range of a dual-polarized phased-array antenna capable of independently steering TE and TM waves. This is achieved by placing a dual-polarized phase-gradient Huygens’ metasurface in front of the antenna. The Huygens’ metasurface employs crossed meander lines in four impedance layers that are suitably optimized to independently control the local electric and magnetic responses for maximizing the transmission for all incident beams. We validate our approach through theoretical analysis, full-wave simulations, and experimental verification. It is demonstrated that the beam-deflecting HMS achieves effective scan range expansion to −30° ∼ 0° and 0° ∼ 30° for TE and TM beams, respectively, using a dual-polarized phased array antenna source that scans from −15° and 15°.