A low-profile dual-band dual-polarized antenna with an artificial magnetic conductor (AMC) reflector is proposed for 5G communications. The antenna consists of a pair of crossed dual-polarized dual-band bowtie dipoles and a dual-band AMC reflector. By introducing trapezoidal slots and U-shaped slots on the bowtie dipoles, miniaturization and dual-band characteristics are achieved. Moreover, T-shaped feeding structures are utilized to broaden the bandwidth of the bowtie dipoles. By adopting a dual-band AMC reflector instead of a conventional perfect electric conductor (PEC) reflector, the distance between the radiator and the reflector can be reduced from $0.25\lambda _{0}$ to $0.08\lambda _{0}$ (where $\lambda _{0}$ is the free-space wavelength at 3.5 GHz). The radiator can maintain the impedance bandwidth and a high gain can also be achieved, even if it is close to the AMC reflector. A geometrical optics model is used to explain the mechanism of the AMC. The optimal parameters of the AMC depend on the antenna operating frequency and the distance between the radiator and the reflector. Measurements show that the proposed dual-band antenna has an impedance bandwidth of 19.8% (3.14-3.83 GHz) and 13.2% (4.40-5.02 GHz), covering the sub-6 GHz frequency spectra of 5G mobile communications. The peak gain is 7.1 dBi in the lower band and 8.2 dBi in the upper band. Port isolation better than 20 dB is achieved. The proposed antenna can be used alone for 5G indoor base station, or as the element of an array for 5G outdoor base station.

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A Low-Profile Dual-Band Dual-Polarized Antenna With an AMC Reflector for 5G Communications

A wideband and low-profile cross-slot pattern reconfigurable antenna for electromagnetic imaging systems is proposed. The antenna is designed to cover the human chest area with steerable unidirectional radiation patterns at 0.7–0.9 GHz. The antenna is comprised of a corrugated cross-slot as the main radiator, and four parasitic slots with four p–i–n diodes operating as reflectors. An embedded feeding network with six p–i–n diodes is used to feed the main slot and switch the feeding path to modify the direction of the radiated beam (vertical/horizontal). In addition, an inductive mesh-grid surface is used to reduce the back lobe and enhance the operating frequency bandwidth. The antenna dimensions are ${0.8} {\lambda }_{0} {\times 0.} {8} {\lambda }_{0} {\times 0.18} {\lambda }_{0}$ (where ${\lambda }_{0}$ is the wavelength of the lowest frequency operation). By turning the parasitic slot p–i–n diodes to ON/OFF modes, the main beam can be steered along five distinctive positions at 0°, and at ±30° in two perpendicular planes. The antenna achieves a peak gain of 9 dBi at 0.8 GHz with 1 dB gain variations over the band of operation with a peak front-to-back ratio of 20 dB.

Two-Dimensional Pattern-Reconfigurable Cross-Slot Antenna With Inductive Reflector for Electromagnetic Torso Imaging

A wideband beam-switching metasurface antenna using programmable unit-cells is proposed for electromagnetic torso scanning. The design aims at changing the intensity of the electric field inside the torso without any mechanical movements and thus enables fast electronic scanning of the torso. The antenna consists of an H-shape microstrip-fed slot as the radiator and a metasurface layer containing 5 × 5 programmable square ring resonator as the superstrate layer. Four PIN diodes are embedded in each cell to alter the electric field intensity within the metasurface layer and consequently switch the radiation pattern in the azimuth plane, elevation plane, and diagonal axis of the metasurface layer. As a proof of concept, a prototype antenna capable of switching the radiation pattern from -25° to +25° in the azimuth (x-z) plane is fabricated and measured. The antenna, which has the compact size of 0.9λ
 0
×0.9λ
 0
×0.06λ
 0
 (where λ
 0
 is the wavelength at the center operation frequency), achieves a wide bandwidth of 30% at 0.9-1.2 GHz. The peak measured gain is 9.5 dBi with maximum front to back ratio of 12 dB. The fabricated antenna is successfully tested on altering the intensity of the electric field at right, center and left sides of a torso phantom.

/pdf/programmable-metasurface-antenna-for-electromagnetic-torso-rltrvpq9wg.pdf

Programmable Metasurface Antenna for Electromagnetic Torso Scanning

A review of hybrid couplers: State-of-the-art, applications, design issues and challenges

This communication describes a wideband switched-beam antenna fed by a compact single-layer beamforming network. First, a novel hybrid coupler structure that can provide an arbitrary phase difference over a bandwidth larger than 58% is proposed with the theoretical analysis. Based on this compact coupler configuration, a wideband $4 \times 4$ Butler matrix is devised with the need for standalone phase shifters and crossovers eliminated. The proposed Butler matrix achieves the widest bandwidth among the single-layer structures up to present. Consequently, a wideband switched-beam antenna array is realized by utilizing the log-periodic endfire antenna elements with bowtie dipoles on the Butler matrix. For validation, a broadband switched-beam antenna array is designed, fabricated, and measured. A stable beamforming performance is ascertained with a gain variation smaller than ±1.66 dB over a bandwidth from 1.98 to 3.14 GHz.

A Wideband Switched-Beam Antenna Array Fed by Compact Single-Layer Butler Matrix

A wideband switched beam antenna array system operating from 2 to 5 GHz is presented. It is comprised of a $4\times 1$ Vivaldi antenna elements and a $4\times 4$ Butler matrix beamformer driven by a digitally controlled double-pole four-throw RF switch. The Butler matrix is implemented on a multilayer structure, using 90° hybrid couplers and 45° phase shifters. For the design of the coupler and phase shifter, we propose a unified methodology applied, but not limited, to elliptically shaped geometries. The multilayer realization enables us to avoid microstrip crossing and supports wideband operation of the beamforming network. To realize the Butler matrix, we introduce a step-by-step and stage-by-stage design methodology that enables accurate balance of the output weights at the antenna ports to achieve a stable beamforming performance. In this paper, we use a Vivaldi antenna element in a linear four-element array, since such element supports wideband and wide-scan angle operation. A soft condition in the form of corrugations is implemented around the periphery of the array, in order to reduce the edge effects. This technique improved the gain, the sidelobes, and helped to obtain back radiation suppression. Finally, impedance loading was also utilized in the two edge elements of the array to improve the active impedance. The proposed system of the Butler matrix in conjunction with the constructed array can be utilized as a common RF front end in a wideband air interface for a small cell 5G application and beyond as it is capable to simultaneously cover all the commercial bands from 2 to 5 GHz.

/pdf/a-cost-effective-wideband-switched-beam-antenna-system-for-a-4qf4pc1oqq.pdf

Tzihat Empliouk

Papers

A Cost-Effective Wideband Switched Beam Antenna System for a Small Cell Base Station