Integrated Vivaldi antenna for UWB/diversity applications in vehicular environment

This article presents the design of a three‐port diversity antenna capable of producing three‐directional radiation pattern for vehicular communications. The proposed antenna consists of three uncorrelated Vivaldi antennas that are interconnected and developed on a single printed circuit board. Unlike many other antennas reported for the vehicular environment, the proposed antenna offers ultra‐wideband characteristics with end‐fire radiation pattern leading to high realized antenna gain. The integrated antenna has a footprint of 65 × 40 × 1.6 mm³ and offers 6 GHz impedance bandwidth extending from 5 to 11 GHz. The port‐to‐port isolation is greater than 20 dB within the operating bandwidth. Furthermore, the diversity performance of the proposed three‐port antenna system is evaluated and presented. The calculated envelope correlation coefficient, diversity gain, and mean effective gain are well above the minimum requirement. The prototype antenna is fabricated and the experimental results are presented.     

一种超宽带相控阵天线单元设计

为了提高相控阵天线的超宽带和宽角扫描性能,提出一种新型全金属Vivaldi天线阵元。利用仿真软件CST对Vivaldi天线阵元建立模型、仿真与优化,最终该天线在2~18 GHz的频段内,其VSWR≤2,具备超宽带特性;针对扫描盲区的问题,提出下宽上窄的创新型侧面结构,优化电流路径,消除扫描盲区,最终可实现全频带范围内±45°的宽角扫描特性。仿真结果表明,该天线具有超宽带、宽角扫描的特性,可以满足作为超宽带宽角扫描相控阵天线单元的要求。     

基于石墨烯材料的太赫兹波段频率可重构八木天线

传统天线中使用电子开关或PIN二极管开关等方式实现天线可重构功能,但是在太赫兹波段上会面临切换速度慢,偏置电路复杂等问题。石墨烯具有优异的电磁性能,可运用于太赫兹可重构天线中。根据石墨烯表面电导率模型,研究其电导率随频率、化学势的变化关系,证明了石墨烯在可重构天线设计中的可行性。设计了一款太赫兹波段石墨烯频率可重构八木天线,通过改变石墨烯贴片偏置电压改变石墨烯化学势,从而改变天线的工作模式。在HFSS软件中进行仿真优化,天线具有300GHz和500GHz两种频率的工作模式,最大增益分别达到9.29dB和10.28dB,表现出良好的辐射特性。     

Design of ultra‐wideband antenna using tapered slot for low‐end frequency extension

In order to extend the lower frequency down, resonant cavities are added to a tapered slot Vivaldi antenna. Using a full‐wave time‐domain method, the effect of the dielectric substrate on the performance of the antenna has been investigated. Permittivity was shown to play an important role in comparisons of wideband frequency range antennas with dielectric constant cases in similar geometries. When dielectric permittivity is increased, the bandwidth is improved, and when the resonant cavity is added, the low‐end frequency response is extended even lower than 500 MHz. Results from a conventional tapered slot edge compared to a tapered slot edge with resonant cavity Vivaldi antennas with different dielectric permittivity qualitatively supports the effect of the different substrate. Verification has been implemented by using the numerical method of pseudospectral time‐domain with alternating‐direction‐implicit method, and by the experiment. The simulation results show very good agreement with the experiment. Both results proved that our design is available.     

Detection of metallic and nonmetallic concealed targets based on millimeter‐wave inverse scattering approach

A millimeter‐wave radar based on active invers scattering approach for two dimensional screening of metallic and nonmetallic concealed targets is presented. The perceived challenges of detecting a nonmetallic target exhibiting poor dynamic range for measurement systems are analyzed and discussed by comparing the performance of three different antenna sensors. A short time duration pulse with frequency sweep covering 27 to 33 GHz band is used to feed the antenna sensors. In our experimental test, we buried a concealed target consists of metallic or dielectric strips under a dielectric layer that simulates the human body model. Waveguide and printed antipodal Vivaldi antennas are considered to study the target detectability and the quality of the measured millimeter‐wave images. The use of proposed AVA resulted in a better‐quality image with lower noise effect for both metallic and nonmetallic cases.     

A single sided dual‐antenna structure for UHF RFID tag applications

In this article, a dual‐antenna structure is presented for UHF RFID tag. The proposed structure is made of two L‐shaped strip antennas along with a cross‐shaped slot loaded patch. One antenna is exclusively used for receiving and harvesting full energy with complex conjugate of tag chip, whereas another used as backscatter to enhance maximum differential radar cross section with purely real input impedance, which results in the enhancement of read range. Further, electromagnetic band gap structure is used around the dual‐antenna structure to increase the gain which results in improved read range. The proposed antennas are fabricated and the S‐parameters are measured with the help of differential probe technique. Simulation and measurement results are found in good agreement. The performance of the proposed antenna is also investigated when it placed on different materials such as metal, wood, glass, and plastic. The study shows that the read range of antenna increases considerably when it is mounted on a metallic surface, while the maximum performance is observed when the antenna is attached on a glass surface with highest relative permittivity. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:619–628, 2015.     

A compact wide‐band antipodal Vivaldi antenna design

A compact wide‐band antipodal Vivaldi antenna (AVA) is designed in this work. First, the traditional exponentially tapered edge of the radiator is replaced by an arc curve that makes the AVA compact. Second, the AVA is loaded with a “director” and a “convex lens” that improve its high‐frequency performance. The proposed antenna is fabricated and its dimensions measured. It occupies a small volume of 34 × 16 × 0.8 mm³ and provides an operating frequency range from 3.01 to 10.6 GHz with a higher gain in the low frequency region than that of reference antennas. The measured results perfectly coincide with the simulated ones, which demonstrates the feasibility of the novel AVA design.     

Wideband high aperture efficiency antennas with beam switching for mmWave 5G base stations

A compact metamaterial inspired sub‐wavelength unit cells are integrated into wideband Vivaldi antenna. A high gain Vivaldi antenna with 50% impedance bandwidth is proposed. The dimensions of the antenna are 1.55 λ₀ × 3.2 λ₀ at 28 GHz. Gain enhancement of 3‐dB achieved by placing metamaterial unit cells in the aperture of the antenna. These unit cells aid in phase correction of the antenna. The 1‐dB gain bandwidth of antenna is 42% with a peak gain of 12.5 dBi indicating high pattern integrity. Corrugations of varying length are introduced in the ground plane to improve front‐to‐back ratio without altering the input impedance bandwidth. The aperture efficiency of the metamaterial loaded Vivaldi antenna is 78% at 28 GHz. The proposed element is used in a stacked module to achieve wide angular coverage of 120°.     

Dual open‐slot antennas integrated in metal frame and metal case of tablet computer for long‐term evolution applications

Dual open‐slot antennas were integrated in the metal back case and metal frame of a tablet computer for long‐term evolution applications. The single feed dual excitation source antennas were sufficiently narrow (2 mm) for installation between the metal frame and metal back case of the tablet computer. Each antenna had two open‐slot radiators (slot 1 and slot 2) with embedded filter circuits to enable wideband (699‐906 and 1710‐2690 MHz) operation required for LTE applications. The filter circuit values were adjusted to make the impedance more smooth and excite the desired modes. The proposed multiple‐input‐multiple‐output antennas were installed lengthwise on the long sides of the tablet and facing in operate directions. In this configuration, the user hand grip did not interfere with antenna performance, and isolation was improved (> 20 dB). The operating mechanism of the proposed antenna with matching circuits is described in detail. The effects of the user hand grip and the embedded display panel are also discussed.     

Low‐profile substrate integrated waveguide (SIW) cavity‐backed self‐triplexed slot antenna

A low‐profile self‐triplexed slot antenna is proposed for multiple system integrations. The antenna comprises of hybrid substrate integrated waveguide (SIW) cavity (a combination of a half‐mode circular and half‐mode rectangular SIW), radiating slot, and feeding network. A slot is imprinted on the upper metal‐layer of the SIW which splits the cavity into three radiating sections. It offers tri‐frequency bands when each section is excited separately. By finely tuning the antenna dimensions, it produces three frequency‐bands around 5.57, 7.17, and 7.65 GHz simultaneously utilizes a single slot with maintaining the intrinsic input‐port isolation better than 20 dB. This property helps to introduce the self‐triplexing phenomenon. Compared with the conventional multiband antennas that use an extra circuitry to ensure the port isolations, this design preserves compactness and easy to integrate with planar circuits Moreover, the proposed antenna is fabricated and the measured results mutually agreed with the simulated counterparts. The proposed design can be a feasible option for mobile transceiver applications.     

Bandwidth enhancement of a circularly polarized tapered crossed slot antenna with corner parasitic directors

This paper presents a single‐feed wideband circularly polarized (CP) antenna with tapered crossed slots and corner directors. According to the multi‐mode resonance concept, the antenna uses two identical cross placed Vivaldi‐like tapered slots as the wideband radiating elements, and four rectangular parasitic patch directors are connected on each corner of the ground for further enhancing the bandwidth. A simple second‐order stepped microstrip line with a via on the other side of the substrate is used to feed the antenna. Two pairs of capacitors and inductors are placed on each slot to realize a 90° phase difference for CP operation. The proposed antenna is designed, fabricated and measured. Simulation results are in good agreement with the measured results that demonstrate a 10 dB impedance bandwidth (IMBW) from 1.98 to 5.71 GHz (3.73 GHz, 97.01%) and a 3 dB axial ratio bandwidth (ARBW) from 2.13 to 3.91 GHz (1.78 GHz, 58.94%). The antenna outperforms most of the reported cross slot antennas for its wide IMBW and ARBW.     

Antenna optimization by hybrid differential evolution

To solve complex antenna design problems, this article proposes a hybrid differential evolution algorithm (DE). The proposed method combines the DE with the simplified quadratic interpolation (SQI) to optimize the performance of the antenna. The DE is the global optimizer, and the SQI is used to fine tune. The hybrid DE is demonstrated on optimizing designing Yagi‐Uda antennas and wideband patch antennas. Numerical results confirm that the proposed method is superior to or at least competitive with the original DE and other evolutionary algorithms in terms of convergence speed and solution quality. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2010.     

High‐conductive graphene film based antenna array for 5G mobile communications

Graphene antennas and relevant microwave devices have attracted wide attention due to their lightweight, low‐cost, and flexible characteristics. However, their performances are usually not satisfactory because of low conductivity of graphene materials in the macroscopic scale. In this article, an antenna array made of flexible high‐conductivity graphene materials is fabricated and reported for potential application in 5G mobile communications. The antenna array has a high gain of 6.77 dBi at 3.51 GHz with an excellent return loss, which is comparable to the identical copper counterpart. Moreover, the graphene antenna has similar radiation patterns to the copper antenna.     

Near optimal conformal antenna array structure for direction‐of‐arrival estimation

This article determines the near optimal conformal antenna array structure for direction‐of‐arrival (DOA) estimation through a comprehensive study on the planar and usual conformal antenna arrays including the cylindrical and hemispherical by using the directive antenna elements in all designs. To model the hemispherical structure, an improved multi‐face antenna array with three different tilts is proposed and compared with previous works in order to investigate the tilt effect and obtain the conclusive results. The Cramer‐Rao lower bound, multiple signal classification, and root‐mean‐square error algorithms are utilized to evaluate the estimation accuracy of all conformal structures. Finally, by comparing the estimation precision of all conformal structures it is shown that the purposed multi‐face structure as the hemispherical model has a better performance than other conformal structures in terms of the maximum angular coverage of the spatial resource. Moreover, the proposed study method in this article fully examines the impacts of the different conformal antennas geometric structure on the DOA estimation performance by involving the directive antennas radiation patterns.     

EBG design and analysis for wideband isolation improvement between aircraft blade monopoles

A new lightweight multilayer mushroom EBG is proposed to significantly improve the isolation between collocated aircraft L‐band blade monopole antennas. Isolation improvement between two L‐bands (960‐1220 MHz) blade monopoles of nearly 20 dB is obtained with a three‐layer EBG design without requiring any redesigning or tuning of the antennas. Since the proposed EBG structure only contains very thin dielectric sheets and foam substrates it would be a lightweight structure. Moreover, the EBG being a stand‐alone structure from the antenna it can be designed, built, and placed between the antennas as an add‐on device to significantly improve antenna isolation over a relatively wide bandwidth (25%). An experimental EBG structure was built and tested demonstrating wideband isolation improvement performance.     

Self‐diplexed antenna based on loading asymmetric grounding‐vias

This article presents a simple and efficient method for the design of a self‐diplexed antenna based on loading asymmetric grounding‐vias. The structure consists of two antenna elements loaded with two asymmetric grounding‐vias, specifying the uplink and downlink operation frequencies. By choosing the appropriate positions of the two grounding‐vias, high isolation between the two antennas can be achieved. To validate the feasibility of the proposed structure, two self‐diplexed antennas with different operational frequencies have been fabricated and tested. Experimental results verify the multi‐functionalities of the proposed compact structure in terms of high isolation and low cross‐polarization discrimination.     

Mutual coupling reduction in planar Yagi antenna array using bidirectional absorbing metasurface

An effective method for reducing the mutual coupling between the antenna arrays using a bidirectional absorbing metasurface is proposed in this article. This is achieved by embedding the bidirectional absorbing metasurface between the two planar Yagi antennas. The metasurface is mainly composed of 3 × 6 unit cells. Each unit cell includes three‐layer metal rings and two‐layer dielectric slabs. Since the front and back of the metasurface are completely consistent, a bidirectional absorptivity can reach to 86% or more. Using the proposed metasurface, the mutual coupling at the resonance point can be reduced to about 38 dB. And it has little effect on other performances of the Yagi antennas. Moreover, the proposed metasurface can improve the radiation performance of the antenna array, and make it have a smaller back lobe and a larger front‐to‐back ratio.     

Pattern reconfigurable metasurface to improve characteristics of low profile antenna parameters

This article proposes a mushroom‐shaped electromagnetic band gap (EBG) structure for the antenna parameter enhancement of low profile antennas in 5 to 15 GHz regime. Three different type antennas including a dipole antenna, a loop antenna, and a monopole antenna are designed for the corresponding operation band, and a 8 × 8 mushroom type EBG structure is designed to obtain exotic behavior for the enhancement of antenna parameters. Bandwidth, return loss (S₁₁), main lobe gain, directivity, side lobe level, front to back ratio, and angular width of each antenna with EBG structure is examined with details. Besides, the designed EBG structure and antennas are fabricated and experimental results are obtained to support numerical ones. In addition, future study of the proposed EBG structure such as microwave imaging in cavity resonators is specified and discussed.     

HFSS8．5在微带缝隙天线设计中的应用

介绍了微带缝隙天线中的维瓦尔迪天线,并借助于Ansoft公司的HFSS8.5软件进行了精确设计,通过将设计值与实验值进行比较,结果吻合。可以看出用EDA软件设计较之于传统的天线设计方法具有的优势,对于工程设计人员具有指导意义。     

Reconfigurable frequency and steerable beam of monopole antenna based on graphene pads

This article presents a reconfigurable frequency and steerable beam monopole antenna based on tunable graphene pads operating in both 4G and 5G bands. The proposed antenna consists of printed CPW‐fed circular monopole shapes, with five rectangular strips added with a separation angle of 45°. These strips are connected to monopole by using graphene pads. The monopole antenna operates in the lower 5G band from 3 up to 7.8 GHz at ?6 dB reflection coefficient. The antenna has an omni‐radiation pattern over the operating band without any applied bias voltage to the graphene pads. By applying the DC bias voltage, the rectangular strips are connected to the monopole and the designed antenna start to resonate from 1.8 to 8 GHz adding the 4G band frequencies. The steering of the proposed antenna beam started from ?60° to 60° according to the bias of the connected graphene pads. The graphene pad exhibits a variable resistance realizing an almost short to an open circuit with and without voltage bias, respectively. The designed antenna is simulated using high frequency structure simulation (HFSS) Ansys ver. 19 and equivalent circuit model of the graphene. The antenna is fabricated using reduced graphene oxide (RGO) pads. Reflection coefficient and radiation pattern measurements as well as simulations are presented with a positive agreement between the results.