The concept of dual-polarized reconfigurable reflectarray (RRA) featuring dual-polarized beam control is proposed and demonstrated using a dual-channel programmable metasurface. The p-i-n diodes are incorporated into each metasurface element as the active components to provide independent phase control in two orthogonal polarization channels. By altering the working states of each p-i-n diode, well-defined beam scanning can be obtained. Element design, focal diameter ratio selection, and discretized phase distributions are carefully optimized to ensure stable radiation performance of the proposed RRA. As verification, a prototype consisting of 20 $\times20$ elements is fabricated and measured, which is controlled by a field programmable gate array-based controller. Measured results show that wide-angle beam scanning up to ±40° can be obtained around 7.45 GHz, with peak gains of 21.13 and 20.89 dBi in dual channels, corresponding to aperture efficiencies of 16.35% and 15.47%. The proposed dual-polarized RRA brings a new freedom in polarization manipulations for versatile beam scanning, which provides promising applications in wireless communication and tracking/detecting systems.

Active metasurfaces pave a way for manipulating electromagnetic (EM) waves in real-time by incorporating with tunable materials or components, emerging as an attractive solution to achieve versatile EM functionalities in dynamic fashions. However, most of the active metasurfaces demonstrated so far only support tunable responses for a certain single frequency band, or have obvious frequency cross-talks that cannot provide dual-band independent operations, limiting their further uses in practical applications. Here, we propose a 1-bit high-efficiency programmable metasurface to achieve completely independent functions with real-time reconfigurability controlled by FPGA hardware system in both C-band and X-band. Specifically, the metasurface is designed with abilities of generating multi-beams or twin-beam scanning in the low frequency band while dynamic beam-scanning in high frequency band. As the experimental verifications, a double-layered metasurface has been fabricated and tested, and the measured results agree well with the simulations, demonstrating its abilities of independent, high-efficiency, real-time, and programmable manipulation of EM waves in two discrete frequency bands. The proposed concept may largely enhance the information capacity of the metasurface, bringing new degrees of freedom in achieving versatile tunable functionalities and offering useful applications in the radar and wireless communication systems.

This paper presents a switchable dual-polarized frequency-selective rasorber/absorber at low microwave frequency based on double-layered metallic resonant structure array loaded with lumped elements. The proposed metamaterial structure consists of an absorbing layer and a bandpass frequency-selective surface layer loaded with PIN diodes, sandwiched with an air-spacer between them. Its operating principle is analyzed with the help of an equivalent circuit model. By biasing the PIN diodes on or off, it can be easily switched between the rasorber and absorber modes. When in the rasorber mode, it exhibits a transmission window at 1.6 GHz with 1.6 dB insertion loss between two neighboring absorption bands. While switched to the absorber mode, it achieves more than 80% absorptivity ranging from 0.8 to 3.4 GHz, corresponding to a fractional bandwidth of 124%. The total thickness is less than 8% of the free-space wavelength at the lowest operating frequency. A prototype of the proposed structure is fabricated and measured, where reasonable agreements between simulations and measurements are observed, verifying the effectiveness of the design.

A novel high-efficiency polarization-selective bifunctional metasurface (MS) is proposed, which can realize cross-polarized focusing transmission for left-handed circular polarization (LHCP) incidence and co-polarized specular reflection for right-handed circular polarization (RHCP) incidence. As an example of its practical application, the designed MS is applied to form an RHCP folded transmitarray antenna (FTA) whose feed source (FS) is integrated with the bottom metallic surface. To prove the concept, a prototype of millimeter-wave (MMW) FTA based on the proposed MS is numerically simulated, physically implemented, and experimentally measured. The measured results coincide well with the simulated ones, showing a peak gain of 23.6 dBi at 27.7 GHz with the peak aperture efficiency of 43.1%, a 3 dB gain bandwidth of 15.8% (25–29.3 GHz), and a 3 dB axial-ratio (AR) bandwidth over 29.6%. The proposed high-performance antenna has the advantages of low profile, high efficiency, integration design, and broad bandwidth, which may have promising applications in the fifth-generation MMW communication system. The proposed MS and its application to high-gain antenna may promote the uses of MS to real-world applications in satellite communication, radar detection, and wireless communication.

In this article, a single-sheet metasurface (MS) for independently manipulating the transmissive phase and amplitude of linearly polarized electromagnetic (EM) wave is proposed. The amplitude modulation is achieved via imposing a rotation angle to flexibly control the ratio of polarization conversion, while the phase modulation is realized by tuning the physical parameters of the unit cell to change its resonance. By integrating the proposed single-sheet MS, a low-profile metalens antenna operating around 12.2 GHz is designed, fabricated, and experimentally validated. In particular, spatially varying amplitude on the MS aperture is designed to meet the Taylor distribution, thus reducing the sidelobe level (SLL) of the metalens antenna. In addition, special MS elements rotation strategy is performed to maintain good polarization isolation-level (PIL) performance. The measured results show that the proposed metalens antenna achieves the peak gain of 25.3 dBi at 12.6 GHz with 3 dB gain bandwidth of 16.4% (11.2–13.2 GHz). Within the 3 dB gain bandwidth, this metalens antenna achieves SLL lower than −20.5 dB with an average value of −23 dB and PIL lower than −22.2 dB with an average value of −26.5 dB. Compared with metalens antenna with phase-only modulations, the proposed metalens antenna realizes a 5.7 dB average SLL suppression. The proposed metalens antenna is a promising candidate in point-to-point communications for wireless and satellite system applications.

In this work, we propose a metamaterial absorber at microwave frequencies with significant sensitivity and non-destructive sensing capability for grain samples. This absorber is composed of cross-resonators periodically arranged on an ultrathin substrate, a sensing layer filled with grain samples, and a metal ground. The cross-resonator array is fabricated using the printed circuit board process on an FR-4 board. The performance of the proposed metamaterial is demonstrated with both full-wave simulation and measurement results, and the working mechanism is revealed through multi-reflection interference theory. It can serve as a non-contact sensor for food quality control such as adulteration, variety, etc. by detecting shifts in the resonant frequencies. As a direct application, it is shown that the resonant frequency displays a significant blue shift from 7.11 GHz to 7.52 GHz when the mass fraction of stale rice in the mixture of fresh and stale rice is changed from 0% to 100%. In addition, the absorber shows a distinct difference in the resonant absorption frequency for different varieties of grain, which also makes it a candidate for a grain classification sensor. The presented scheme could open up opportunities for microwave metamaterial absorbers to be applied as efficient sensors in the non-destructive evaluation of agricultural and food product quality.