This study presents a new class of independently polarization manipulable liquid-crystal (LC)-based reflective metasurface antenna. To the best of the authors’ knowledge, this study first introduces independent polarization controllability of the LC-based reflective metasurface in mmWave. Two LC layers are embedded into the proposed structure for independent manipulation of the polarization. Isolation topologies, such as rectangular patch shape and metal strip ground, are utilized to enhance polarization purity, achieving compact bias configuration. The independent polarization controllability and antenna performance, such as aperture efficiency, sidelobe level, and beam coverage, are validated as a reflectarray. The proposed antenna has a maximum aperture efficiency of 22.5% and beam coverage of over 120°. In addition, the proposed metasurface is employed to achieve link connectivity as a reconfigurable intelligent surface (RIS) at millimeter-wave 5G. The demonstration confirms a small aperture RIS concept, considering spillover and taper efficiencies.

This paper introduces a novel method for implementing a liquid crystal-based transmitarray (LCTA) antenna with two-dimensional (2D) beam scanning capability for the first time. Extending the phase tuning range of LCTA unit cells faces a crucial limitation in maintaining a thin single liquid crystal (LC) layer because the tuning range is significantly dependent on the LC thickness. The proposed transmission line-based unit cell design could overcome this limitation due to its horizontal propagation characteristic among the LC layers. Therefore, the proposed LCTA unit cell achieves a phase tuning range of 130° while maintaining the thickness of the LC under 0.25 mm at 28 GHz. Furthermore, a 10 × 10 array design is fabricated and measured to verify its 2D beam scanning capability. Consequently, the maximum scanning angle of 30° is obtained in the E-plane and H-plane from measurements. Comparative results with previous studies also emphasize the advantages of the proposed design.

This study presents a novel electromagnetic analysis and mathematical derivation for determining the locally optimal unit cell period that minimizes phase error losses in the macroscopic design of a periodic two-metal-layered refractive metasurface (TRM) for outdoor-to-indoor (O2I) communication. The TRM's periodicity is investigated for three main advantages: reducing design complexity, lowering lifecycle costs, and increasing area efficiency. The existence of locally optimal unit cell periods for each pair of incidence and refraction angles, along with a method to find them, was derived. Finally, a 6 G upper-mid optically transparent TRM with a locally optimal unit cell period was fabricated, and its path losses in both far-field and near-field scenarios were measured to validate the proposed technique.

This paper proposes a low voltage controlled fast beam switchable liquid-crystal-based reflectarray (LC-RA). By introducing a strip array of ground patterns and a transverse rubbing layer, a 1.5 V-powered falling response can be achieved for fast beam switching. Typically, the falling response of the LC cannot be controlled by the bias voltage, leading to slow beam switching. The strip array, in conjunction with the top electrodes, generates lateral fields for arranging the molecules of the LC, enabling the falling nature to be controlled by the bias voltage. In addition, the transverse rubbing layer achieves a low voltagebased fast-falling response without degradation of antenna performance. This study demonstrates the antenna performance and switching speed of the proposed LC-RA and compares it with other LC-based antennas. Finally, the proposed antenna achieves 1.6 sec of switching speed with under bias voltage of 5 V for the beamforming. Moreover, the proposed design shows high antenna performance, such as aperture efficiency, SLL, and scanning range, compared to the LC-based antennas at the mmWave band.

This letter proposes a near-field beam focusing transmitarray-based (TA-based) free space measurement system that is extremely miniaturized rather than horn-to-horn and dielectric lens-based measurement systems for radio frequency (RF) metamaterial composites. Reducing the size of the measurement setup is limited due to the natural phenomenon of conventional systems. Contrastively, TA-based system could overcome the limitation because of its phase-shifting ability to maintain the planar appearance. A device-under-test (DUT) was measured without any distortion utilizing the beam focusing characteristic of the proposed TA, which produces a uniform wavefront phase without diffraction over the DUT aperture. The proposed TA could focus the EM wave within a distance of 2 cm from the horn antenna while maintaining the phase error under $14.5^\circ$ , resulting in a plane wave-like phase. Consequently, the RF metamaterial composites could be measured at a short focal distance of 21.7% of the distance required by the conventional free-space system without additional absorbers. Further, the frequency response of DUT (i.e., $|S_{21}|$ and $\angle S_{21}$ ) could be obtained adequately compared to the full-wave simulation. The difference of transmission zero frequency between simulation and measurement was less than 1.6%.

This article presents a low-power consumption and beam-holding reconfigurable intelligent surface (RIS) for reliable millimeter-wave 5G fixed wireless communication. Conventional RIS designs require continuous power to maintain beamforming, with power consumption divided into two main parts: power drawn by the control board and power dissipated by unit cells. The strategies for reducing power consumption differ based on the adjustable components used. In this study, a liquid crystal (LC)-based RIS is employed to achieve low-power consumption, alongside a customized bias circuit that incorporates switches and capacitors. The proposed circuit operates using bias pulses, allowing charges to be stored in the capacitors, which in turn ensures beam sustainability. Prior research on LC-RIS reported the need for continuous power consumption and complex bias nodes to control the LC. Moreover, the proposed RIS, consisting of an ${N} \times {N}$ array, requires only $2{N}$ bias nodes for 2-D beamforming, unlike traditional RIS designs. This innovative biasing approach, referred to as an active-matrix scheme, enables a low-power, beam-sustainable RIS architecture and can be effectively applied to electrically large RIS arrays with 2-D beamforming capabilities.