In this letter, a novel method of reducing mutual coupling is proposed, and it used on a modified compact broadband antipodal Vivaldi antenna (AVA) array for future 5G millimeter-wave (mmWave) communication application. The proposed structure consists of eight antenna elements that are fed by a 1-to-8 power divider. In order to reduce the mutual coupling between AVA array elements, multiple notch structures are added on the ground plane. Thus, the isolation between the antenna elements can achieve a maximal additional 37.3 dB enhancement, impedance bandwidth is extended slightly from 24.65–28.5 GHz to 24.55–28.5 GHz, and the gain is improved simultaneously. To verify the designed method, the proposed AVA arrays were fabricated and measured. They show an overall size of 28.823 mm × 60 mm × 0.787 mm. The measured gain of the modified AVA array is 6.96–11.32 dB in the frequency band of future 5G mmWave communication, which is higher than the initial AVA array, whose gain is 5.34–8.5 dB.

A Compact Gain-Enhanced Vivaldi Antenna Array With Suppressed Mutual Coupling for 5G mmWave Application

The terahertz (THz) antennas, which have features of small size, wide frequency bandwidth and high data rate, are important devices for transmitting and receiving THz electromagnetic waves in the emerging THz systems. However, most of THz antennas suffer from relatively high loss and low fabrication precision due to their small sizes in high frequency bands of THz waves. Therefore, this paper presents a detailed overview of the most recent research on the performance improvement of THz antennas. Firstly, the development of THz antennas is briefly reviewed and the basic design ideas of THz antennas are introduced. Then, THz antennas are categorized as metallic antennas, dielectric antennas and new material antennas. After that, the latest research progress in THz photoconductive antennas, THz horn antennas, THz lens antennas, THz microstrip antennas and THz on-chip antennas are discussed. In particular, the practical difficulties for the development of THz antennas are discussed with promising approaches. In addition, this paper also presents a short review of the process technology of THz antennas. Finally, the vital challenges and the future research directions for THz antennas are presented.

An overview of terahertz antennas

A novel compact, planar, and coplanar waveguide (CPW)-fed dual-band antenna is designed and proposed using composite metamaterial. Such composite metamaterial consists of an inner split-ring resonator (SRR) and an outer closed-ring resonator (CRR). The composite metamaterial can provide dual-band operation at 2.595-2.654 and 3.185-4.245 GHz with reflection coefficient better than -10 dB by the two resonant modes of SRR and CRR, respectively. A CPW-fed line with trapeziform ground plane and tapered impedance transformer line is employed to improve the impedance matching of the antenna. The uniqueness of this design is that the inner SRR with size much smaller than the resonant wavelength is used for obtaining the lower narrow frequency band, which makes the dual-band antenna very compact. Antenna parameters, including reflection coefficient, radiation pattern, radiation efficiency, and gain, are analyzed with numerical simulation and experimental measurement. Good agreement between the simulation and measurement is observed.

A Compact, Planar, and CPW-Fed Metamaterial-Inspired Dual-Band Antenna

A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems.

/pdf/wideband-and-uwb-antennas-for-wireless-applications-a-1yabyj5rhz.pdf

Wideband and UWB Antennas for Wireless Applications: A Comprehensive Review

(1979). Gradient Index Optics. Optica Acta: International Journal of Optics: Vol. 26, No. 4, pp. 426-427.

Gradient Index Optics

Although the microstrip antenna has been extensively studied in the past few decades as one of the standard planar antennas, it still has a huge potential for further developments The paper suggests three areas for further research based on our previous works on microstrip antenna elements and arrays One is exploring the variety of microstrip antenna topologies to meet the desired requirement such as ultrawide band (UWB), high gain, miniaturization, circular polarization, multipolarized, and so on Another is to apply microstrip antenna to form composite antenna which is more potent than the individual antenna The last is growing towards highly integration of antenna/array and feeding network or operating at relatively high frequencies, like sub-millimeter wave or terahertz (THz) wave regime, by using the advanced machining techniques To support our points of view, some examples of antennas developed in our group are presented and discussed

https://downloads.hindawi.com/journals/ijap/2012/428284.pdf

Some Recent Developments of Microstrip Antenna

Antipodal curvedly tapered slot antennas (ACTSAs) with different slot profiles are investigated to achieve the optimum circular polarization performance. The profiles of the tapered slots can be determined by different curves, such as linear, exponential, and logarithmic curves. Therefore, the corresponding waveguide-fed circularly polarized (CP) antipodal linear, exponential, exponential-logarithmic tapered slot antennas (AL-, E-, EL-TSA) are designed, fabricated, and measured at Ka-band for a comprehensive study. The optimized AELTSA provides good impedance matching, gain above 10.3 dBi, sidelobe lower than $-15 {\rm dB}$ , low cross-polarization, and left-hand circularly polarized (LHCP) axial ratio (AR) lower than 3 dB, from 28 to 40 GHz. Moreover, a waveguide-fed LHCP antipodal exponential–exponential tapered slot antenna (AEETSA) is designed at 500 GHz and fabricated by silicon micromachining. The radiation characteristics are examined by measurement results of symmetric beams and ARs lower than 1.5 dB, from 490 to 510 GHz.

Millimeterwave and Terahertz Waveguide-Fed Circularly Polarized Antipodal Curvedly Tapered Slot Antennas

This paper presents a Luneburg lens and a Luneburg reflector lens along with the corresponding compact and cost-effective multibeam antennas in the Ka -band. The Luneburg lens is composed of an air-filled parallel plate waveguide (PPW) loaded with equal-sized metallic posts. The upper plate of the PPW is designed to a curved surface to meet the requirement of the equivalent refractive index profile, meanwhile providing a transition between the lens and the feed waveguide. Also, based on the law of reflection, a reflecting wall is introduced to the Luneburg lens to achieve a Luneburg reflector lens. By employing the WR28 rectangular waveguides as the feeders, the Luneburg lens/reflector lens antennas with single beam and multiple beams are designed and experimentally verified in the whole Ka -band. The multibeam Luneburg lens antenna show the beam scanning from −45° to +45° with 0.6 dB scan loss. The multibeam Luneburg reflector lens antenna show the beam scanning from 30° to 60° with 0.7 dB scan loss. Besides, the acceptable performances of aperture efficiency, impedance matching and multiport isolation are achieved. The results indicate that the works in this paper have application potential in the millimeter-wave (mmW) wireless communications.

Compact Air-Filled Luneburg Lens Antennas Based on Almost-Parallel Plate Waveguide Loaded With Equal-Sized Metallic Posts

A novel compact planar microstrip-fed quaisi-Yagi antenna is investigated. The feeding structure is directly realised by a microstrip line and has the advantage of avoiding the introduction of a balun, transition, tapered or truncated structures, thereby decreasing design complexity. The proposed antenna shows measured impedance bandwidth from 2.74 to 4.25 GHz for a return loss less than −10 dB, and exhibits 13 dB front-to-back (F/B) ratio, –15 dB cross-polarisation, 8.77 dB absolute peak gain, 60° half power beam width (HPBW) in the E-plane and 68° HPBW in the H-plane at the centre frequency (3.5 GHz). Measured results are in good agreement with electromagnetic simulations.

Compact planar microstrip-fed quasi-Yagi antenna

This article presents a Ka -band fully metallic crossover-in-antenna based on an anisotropic lens. The crossover-in-antenna is a multifunction device simultaneously acting as a waveguide crossover and a multibeam antenna. The anisotropic lens performs like a Maxwell fish-eye (MFE) lens and a Luneburg lens in different incident directions, supporting the transmission and radiation, respectively. The lens consists of a parallel plate waveguide (PPW) with gradient spacing loaded with periodic uniform cuboid posts, which can be treated as an array of anisotropic subwavelength unit cells with gradient equivalent refractive indices. The WR28 waveguides are employed as the input–output ports. A flare is added to improve the radiation and impedance matching of antenna channels. According to the experimental results, a waveguide crossover is well realized with the reflection coefficients lower than −15 dB and insertion losses mostly lower than 1.4 dB from 28.7 to 38.2 GHz. Meanwhile, a multibeam antenna with four independent beams is obtained in the whole Ka -band, showing the gains higher than 12.5 dBi and the radiation efficiencies higher than 87.8%. The results indicate that the proposed crossover-in-antenna has application potential in the high-density multifunction integration of millimeter-wave (mmW) systems.

Hongda Lu

Papers

Some Recent Developments of Microstrip Antenna

Millimeterwave and Terahertz Waveguide-Fed Circularly Polarized Antipodal Curvedly Tapered Slot Antennas

Compact Air-Filled Luneburg Lens Antennas Based on Almost-Parallel Plate Waveguide Loaded With Equal-Sized Metallic Posts

Compact planar microstrip-fed quasi-Yagi antenna

Fully Metallic Anisotropic Lens Crossover-in-Antenna Based on Parallel Plate Waveguide Loaded With Uniform Posts