Search

A wideband omnidirectional circularly polarized (CP) antenna using a conformal artificial anisotropic polarizer is proposed for millimeter-wave applications. The antenna consists of three parts: an omnidirectional linearly polarized (LP) radiator, an annular hyperbolic lens, and a conformal anisotropic polarizer. The annular hyperbolic lens regulates the spherical wavefront from the LP radiator into a cylindrical shape prior to propagating into the conformal artificial anisotropic polarizer. Each curved slab of the polarizer is conformally tilted 45 degrees to the incident electric field. Therefore, the conformal polarizer is the three-dimensionalization of the two-dimensional planar artificial anisotropic polarizer. The polarizer designing methodology is the first of its kind to generate wideband CP wave omnidirectionally. The hyperbolic lens and the conformal polarizer are fabricated together using stereolithography (SLA) 3D printing technology. Measurement results show that the antenna has a wide operating bandwidth of 45% (from 24 to 38 GHz), which completely covers potential 5G 28-GHz spectra. The proposed design has a low fabrication complexity and brings possibilities for high-speed wireless communications utilizing circular polarization.

A novel planar dielectric polarizer made of a low-profile high dielectric constant material is proposed. Two anisotropic anti-reflection layers are used on both sides to provide impedance transformation and anisotropy simultaneously. The proposed design uses a high-dielectric-constant material to reduce the overall thickness without severe reflections. The unit cells of the middle layer and the anti-reflection layer use separate periods for better adapting to the fabrication limitation. A polarizer prototype centered at 24 GHz is designed, fabricated, and measured. The prototype is 3D-printed by commercial fused-deposition-modeling (FDM) technology using a material with a dielectric constant of 10. Experiments show the prototype has a 25% operating bandwidth and a thickness of 0.52λ0 (λ0 is the wavelength in the free space). The design methodology widens the choice for material selection and reduces the dimensions of the dielectric polarizer.

A novel compact magneto-electric (ME) dipole antenna with size of 0.31λ0×0.31λ0×0.12λ0 (λ0 is the wavelength at central frequency herein and after), gain of around 8 dBi, and bandwidth of 39.7% is presented for millimeter-wave beam steering applications with the combination of the fractal technique and reactive impedance surface (RIS) loading. In particular, a fractal ME dipole antenna with four modified second-order Minikowski structures is firstly designed, where an aperture size of 0.38λ0×0.38λ0 is achieved. Herein, the antenna gain is dropped with the size reduction. Then a capacitive RIS structure is designed and loaded to improve the antenna gain and further lower down the antenna operating frequency range. With the RIS structure, the antenna gain is increased by around 4 dB, and the operating center frequency is shifted to left side by 9.0 GHz, thus achieving a further size reduction. Simulation and measurement results are provided to demonstrate the excellent properties of the proposed antenna. Subsequently, the antenna is arranged into a 5 mm-spaced (half wavelength at 30 GHz) 16-element uniform linear array. The beam steering characteristics of the array are investigated with the influence of phase quantization errors into consideration.

A new method is proposed to suppress the sidelobe level (SLL) of antenna array. Different from the conventional amplitude-tapered excitation method, ‘±1’ excitations are used to feed the antenna array and achieve low SLL. The SLL is first optimized by using a modified binary particle swarm optimization algorithm with ideal ‘±1’ excitations. Then, the ideal ‘±1’ excitations are replaced with microstrip line feed and aperture-coupled magnetoelectric (ME) dipoles. The ‘+1’ excited ME dipoles are fed from the default direction, while the ‘−1’ excited ME dipoles are fed from the direction physically reversed. According to the optimized array configuration, combining the ME dipole elements with a 256-way parallel power divider, a planar $16\times16$ millimeter-wave antenna array is designed, fabricated, and measured. An overlapped working bandwidth of 38% (24.1–35.4 GHz) is obtained with an SWR less than 2.4 and SLL lower than −17.2 dB. The gain is up to 26.3 dBi. The new binary concept paves a new way for SLL suppressing.

The major axis of the elliptically polarized wave generated by a linearly polarized (LP) radiating source and an artificial anisotropic polarizer has been analyzed in this communication. Both theoretical and experimental results show that the major axis of the elliptically polarized wave generated by such a combination has an angle of 0° or 90° to the E-plane of the LP radiator. The angle between the major axis and the E-plane depends on the phase difference of the two orthogonal electric components after propagating through the polarizer. Measurement has been conducted for verification which covered the entire V-band (50–75 GHz). The result in this communication provides instructions for the usage of artificial anisotropic polarizers in detection and measurement, such as the calculation of the polarization efficiency during transmission.

This communication reports a broadband circularly polarized (CP) reflectarray operating at $X$ -band. An asymmetric dual-polarized magneto-electric (ME) dipole is proposed as the reflectarray element to realize broadband cophasal far-field radiation based on the element rotation technique. Broad bandwidth and high-purity circular polarization are achieved. The fabricated prototype shows a 1.5 dB axial ratio (AR) and 3 dB AR bandwidth of 37% and 42%, respectively. Peak gain of 25.4 dBic and peak aperture efficiency of 60% are experimentally obtained. The aperture efficiency remains higher than 45% over a wide bandwidth spanning from 8.3 to 12.4 GHz. Specifically, the proposed element can be realized on an air gap-free low-profile single-board substrate configuration, owing to the wideband characteristic of the ME dipole. This comparatively robust and easy-to-fabricate structure would be desirable for many applications including broadband satellite communications.

A wideband compact magnetoelectric (ME) dipole antenna is investigated for millimeter-wave applications. First, an aperture coupled ME dipole is proposed with wideband and low profile. Next, transverse slots are added to miniaturize the antenna. The radiation performance of the higher-order mode is also improved. The antenna is finally miniaturized to $2.5\times3.3$ mm2 ( $0.27\,\,\lambda _{0} \times 0.35\,\,\lambda _{0}$ , where $\lambda _{0}$ is the wavelength in free space at center frequency) when it is used in the array environment. A bandwidth of 48.8% (24.3–40 GHz) for SWR $1 \times 8$ linear array is designed, fabricated, and measured. Good beam scanning capability is also verified by active simulation. With the advantages of wide bandwidth, compact size, promising radiation pattern and wide-angle beam scanning potential, the proposed antenna would be attractive for millimeter-wave devices and antenna in package (AiP) applications.

This letter presents a circularly polarized (CP) discrete lens with large operating bandwidth and optimized thickness. A wideband polarization-twisting unit cell, which enables the polarization agility of the lens at a pixel level, is developed using the magnetoelectric-dipole-based transmissive element. By comprehensively utilizing the rotation freedom of the probes at the transmitting and the receiving layers as well as incorporating additional dielectric-coating layer, an over-2-bit CP discrete lens is achieved, demonstrating a wide axial ratio (AR) bandwidth, an improved antenna gain, and a well-controlled lens thickness. A maximum gain of 21.5 dBic and an overlapped 3 dB gain and AR bandwidth of 47% are experimentally achieved with the designed 0.66-λ0-thick, 256-element discrete lens.

An open resonator antenna for orbital angular momentum (OAM) generation and dual-mode application is proposed. The excitation of OAM mode is deduced by the open resonator theory and the circular array theory. In the cavity, eight aperture coupled patch antenna elements are used to excite two higher-order Laguerre–Gaussian HE21 modes with a 90° phase difference. Verifying by simulation and experiment, the proposed low-profile antenna can radiate left-hand or right-hand circularly polarized waves of OAM modes $l=\pm 1$ , which have a relatively low divergence angle of ±9° and high gain of around 13 dBi.