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A three-layer multifunctional metasurface structure is proposed to achieve polarization rotation, perfect polarization conversion, and asymmetric transmission. The design consists of mutually perpendicular rectangular patches, metal pillars, and open-slit metal sheets. By propagating the current through the metal pillars and changing the surface current direction, the dipole can be orthogonally steered to accomplish polarization conversion. The metal in the middle layer can be used to both improve the polarization conversion ratio and ensure high transmittance. The operating band of asymmetric transmission is 8.3–14.7 GHz, where the conversion ratio is above 90% in all of 9–14.2 GHz. In order to verify the proposed concept, the related parameters are designed and measured, the final experimental results match with the simulation results, and the design can be used in the radome, electromagnetic stealth. [ABSTRACT FROM AUTHOR]

A high gain antenna system based on a phase gradient metasurface (PGM) with a four-split ring (FSR) structure is proposed in this letter, which combines the radiation functionalities of transmission-mode, bidirectional-mode, and reflection-mode. The Vivaldi antenna, as a feed source, is placed at the focal point of the metasurface (MS). Then the quasi-spherical wave launched by the feed source undergoes abnormal refraction and reflection when passing through PGM, which proves that the PGM proposed can control the wavefront by altering the frequencies so that the proposed antenna can achieve multimode radiation. In contrast with traditional unidirectional antenna, the proposed antenna has beam converge characteristic in transmission direction at 15.7 GHz with a peak gain of 20.4 dBi, bidirectional radiation at 16.5 GHz, and reflection direction at 17.1 GHz with a peak gain of 16.5 dBi. The results of the simulation and experiment are in good consistency. The proposed PGM has potential applications in designing high-performance multifunctional antennas in communication systems. [ABSTRACT FROM AUTHOR]

A compact antipodal Vivaldi antenna (AVA) with metamaterial half-lens (MHL) for beam control is proposed. The proposed AVA has three different beam forms in the operating frequency band, including end beam from 3 GHz to 9 GHz, beam splitting at 12.2 GHz, and beam deflection at 13 GHz. Furthermore, it can perform beam scanning by adjusting operating frequency from 12.7 GHz to 13.5 GHz. The simulation indicates that the proposed AVA has a −10 dB impedance bandwidth of 143.6% (2.3–14.0 GHz) and a −3 dB gain bandwidth of 100% (4.5–13.5 GHz), which is consistent with the experimental results. Besides, the gain of the proposed AVA has an improvement of about 2 dB in the working band. As a new method to control the beam, the loading of MHL realizes the design of a small size and multi-function antenna, which can be widely used in wireless communication systems. [ABSTRACT FROM AUTHOR]

A kind of compound optical lens (COL) inspired by metamaterials whose unit cell is a closed symmetric S‐type resonator (CSSR) is designed to enhance the gain and directivity of the antipodal Vivaldi antenna (AVA). COL, composed of a plano‐convex lens and a double‐convex lens, can generate a very narrow beam with a half‐power beamwidth of 11.2° at 12 GHz. Traditional metamaterial lenses can only convert spherical waves into plane waves. Although the gain will increase, the beamwidth of the antenna is still very wide. COL can focus the plane wave transformed from the spherical wave, which makes the radiation beam extremely narrow. The proposed antenna has a −10 dB impedance bandwidth of 169.2% (1.0‐12.0 GHz) and a −3 dB gain bandwidth of 133.3% (2.0‐10.0 GHz) and a maximum gain enhancement of 5 dBi. The experimental results of the antennas agree with the simulation results. The proposed antenna is eventually a suitable candidate for wireless communications and radar applications. [ABSTRACT FROM AUTHOR]

A water-based switchable absorber/reflector (WSAR) based on toner-coated honeycomb is proposed. The structure consists of a metasurface absorbing layer, a toner honeycomb layer, a water layer and a metal plate. The combination of metasurface and coated toner honeycomb can realize the function of broadband absorption, and the water layer is used as a control purpose to obtain a good reflection effect by filling the container with water. When the water container is in the state of without water, it behaves as an electromagnetic wave absorber with good absorption performance in the frequency band of 4.72–17.50 GHz. When the water container is in the state of full water，it behaves as a reflector with good reflection performance (reflection coefficient close to −1 dB in the 4.5–10 GHz band) in the operating frequency band. The characteristics and mechanism of the WSAR are analyzed by using the energy loss and equivalent impedance matching, and the correctness of the design is verified by experiments. The proposed structure has certain application value in radar target stealth, electromagnetic compatibility, adaptive camouflage. • The combination of metasurface and honeycomb coated with carbon powder is used to realize broadband wave absorption. • The combination of water layer and composite absorber provides a new idea for switchable absorber/reflector. • Broadband, Multifunctional, Water-based metasurface, Toner coated honeycomb, Wide angle of incidence stability. • Energy loss, surface current analysis,impedance matching and parameter analysis are used to analyze the mechanism. • The structure has certain application value in radar target stealth and adaptive camouflage. [ABSTRACT FROM AUTHOR]

In this paper, a broadband circularly polarized array antenna is presented, which consists of four loop slot antennas based on metasurfaces. The antenna element is a loop slot antenna fed by a microstrip line. Cross slots are added to the loop slot to improve the antenna bandwidth, and four corner-cut square metasurfaces are loaded above it, thus generating circularly polarized radiation. The antenna adopts a sequential phase (SP) feed network to realize broadband characteristics. The antenna has been fabricated and experimented. The overall size of the antenna is 78 × 78 × 10.1 mm3 (approximately 1.22 λ0 × 1.22 λ0 × 0.15 λ0), the antenna array has a measured |S11| < −10 dB bandwidth of 3.6–6.2 GHz (53.1%) and a 3-dB axial ratio bandwidth of 3.7–4.8 GHz (28.32%). Furthermore, the antenna also has radiation with a peak gain of 5.5 dBi. [ABSTRACT FROM AUTHOR]

The metasurface is a functional film device based on a subwavelength structure, which has a strong light field control ability and has the advantages of ultrathin, low loss, and easy manufacturing. However, realizing a multifunctional metasurface, yet simple enough to design, manufacture, and thin is still a challenge. In this article, we propose a novel metasurface with negligible thickness as a beam splitter, which can achieve half transmission and half reflection of the incident wave at the same frequency. It also controls the polarization of circularly polarized electromagnetic (EM) waves in the transmission mode. A broadband operation can be achieved based on the geometric phase theory, and the phase control can be achieved by azimuth rotation of the structure. The numerical results of the metasurface are in good agreement with the experimental results in the measured frequency range. The ultrathin multifunctional metasurface realized by the geometric phase principle provides an important stepping stone for simple optical devices and can be extended to a higher frequency range. [ABSTRACT FROM AUTHOR]

A novel polarization insensitive ultrawideband frequency selective rasorber (FSR) based on a 3-D cubic structure is proposed, and the fundamental operating principles of the three parts are demonstrated by equivalent circuit models. The first one is a 3-D FSR based on the multiple resonant absorptions of the curved longer dipole and shorter dipole excitation in the resonance chamber and the insertion of the interdigital resonator (IR) structure in the shorter dipole to form a transmission window. The passband with an insertion loss of less than 3 dB is 10.3–12.9 GHz (22.4%), and the frequency bandwidth with a reflection coefficient of less than −10 dB ranges from 4.2 to 20.5 GHz (132%). The second is a reconfigurable frequency selective surface (FSS) with two operating states, and the third is a 3-D FSR with a switchable passband feature that incorporates the above two structures of loaded switching diodes. [ABSTRACT FROM AUTHOR]