一种正六边形嵌套分形超宽带天线的设计

针对当前超宽带天线存在的方向性差、增益小的现状,提出了一种正六边形嵌套分形的超宽带天线。天线利用嵌套分形结构的自相似性和空间填充特性,有效拓展带宽,缩减天线尺寸。通过对天线维数进行仿真分析,选择带宽满足超宽带指标的四维和五维天线;对四维天线和五维天线的E-H面方向图及增益进行对比得知,五维天线较高增益由方向图畸变产生,故选择方向性更好的四维天线为此次设计的目标天线。目标天线尺寸仅为20 mm×23 mm×1.6 mm,带宽为2.7~10.6 GHz,增益为1.8~7.8 dBi,且天线实现了良好阻抗匹配。与引文其它天线相比,目标天线具有较小的尺寸,同时具有良好的方向性和较高的增益。天线实测结果与仿真基本吻合,验证了其研究与应用价值。     

Ku波段TM01模介质透镜加载天线

随着高功率微波技术的发展,适用于辐射高功率轴对称模的天线备受关注。基于一般圆锥喇叭天线多用于TE11模的辐射,对TM01的辐射存在缺陷,针对高功率、小型化、较高增益以及最大辐射方向在天线轴向的要求,提出一种多扇区介质透镜天线,介质采用扇形台阶的形式加载在喇叭天线口径的前端,可以进行相位补偿,并使得天线的方向性变好。利用HFSS仿真软件分析表明,所设计的Ku波段的透镜天线具有较好的方向性和增益。     

口径天线方向性系数和增益的快速估算方法

导出了用天线方向图的半功率波束宽度快速计算口径天线方向性系数和增益的简单表达式，分析讨论了这些公式的应用范围。最后，给出了卫星通信天线的增益测量实例，实验结果表明：用半功率波束宽度快速计算的天线增益与其它方法测量的天线增益吻合很好，从而证明了这种方法的正确性。     

Short cylindrical antennas with enhanced radiation or high directivity

The feasibility of enhancing the radiated power or improving the directivity of a short cylindrical antenna by double impedance loading is investigated. An approximate solution for the current on a doubly loaded short antenna is developed, and typical current dlstributions, impedances, and radiation patterns of antennas appropriately loaded to implement enhanced radiation or high directivity are presented. Significant improvements in radiated power or directivity can be achieved with optimum impedance loadings. Theoretical predictions are verified by the results of an experimental study.     

Improving MIMO capacity with directive antennas for outdoor-indoor scenarios

MIMO systems are usually associated with high scattering isotropic propagation while the use of directive antennas is associated with free space conditions. We found outdoor-indoor channels to be in between these two extremes, in the sense that we observed directivity - and - MIMO gain, for the same ensemble of channels. Our observation is based on measurements with directive (8 dB) and dipole antennas. Median MIMO capacities were found to be about 80% of the ideal (Rayleigh i.i.d.), at 5 dB Signal to Noise Ratio (SNR), for both types of antennas. Using properly aimed directive antennas, the SNR was found on average to be 5.4 dB above that obtainable with dipoles, somewhat less than the 7 dB antenna gain difference. Thus, isotropic propagation, which would have negated directivity gains, cannot be justified in general. We empirically established that aiming for largest received power is the best array pointing strategy with directive antennas. Combining MIMO processing and angular search resulted on average in gains of 70% over the median capacities obtained with dipoles. Therefore it may in some cases be convenient to arrange subgroups of antennas for beamforming, and then process the thus reduced number of radio channels for MIMO gain.     

一种新的无源偶极子天线辐射效率测量方法

提出一种无源超高频(UHF)射频偶极子标签天线在自由空间中辐射效率的测量方法并通过仿真和实验对其验证。辐射效率是标签天线的一个重要性能参数,通过测量标签天线的3个基本参数,即方向性系数、实际增益和功率传输系数得出结果,最后对比仿真与实测结果,两者取得良好的一致性,验证了该方法是可靠的。该方法的一个主要优点是可以在实际应用环境中对标签天线辐射效率进行测量,具有广阔的潜力。     

24 GHz On-Chip Antennas and Balun on Bulk Si for Air Transmission

The conditions are investigated under which standard digital bulk Si technology can yield efficient on-chip antennas and baluns for fully differential transmitter and receiver implementations. The effects of the IC material properties and the antenna geometry on radiation and impedance characteristics have been studied. 24 GHz on-chip antennas on lossy Si have been successfully demonstrated, using a standard IC fabrication compatible Cu process. The fabricated antennas demonstrate a gain ranging from 8- to - 10.5 dBi, which is to the best of the author's knowledge, the highest gain reported for antennas in a 10 Omega-cm Si substrate to date.     

平板端射天线组阵的研究

传统端射天线是中等增益天线,不能满足雷达等对高增益的要求。为了提高增益和方向性,把平板端射天线单元进行了组阵。经过大量的仿真分析并结合原有试验结果,发现了平板端射天线的组阵不符合常规天线组阵理论。端射天线阵的增益随着天线单元间距的增大而提高,并且间距在1．5倍波长时天线阵的增益最高。这种特殊的天线组阵形式值得进一步研究。     

近地短波鱼骨天线矩量法建模及应用

结合等效电路理论和离散复镜像方法,对架设在有耗地面上方的水平鱼骨天线进行矩量法建模,计算了其短波段内的输入阻抗、方向图、效率和增益.在分析双鱼骨天线的基础上,从抗极化衰落的角度提出并分析了一种正交鱼骨天线.仿真结果表明,所用方法准确地考虑了有耗地面的影响以及各振子间的互相耦合,具有很高的精度.     

Optimal Lossy Matching by Pareto Fronts

Although lossy matching is not a standard antenna matching technique, well-designed losses can facilitate wide-band matching of otherwise unmatchable antennas. The lossy matching designs developed in this paper are based on the Pareto front. These Pareto front computations permit the circuit designer to graphically select optimal gain-reflection tradeoffs for lossy matching, readily incorporate other lossless matching bounds, and provide a general approach to difficult wide-band matching problems.     

Antennas for VHF/UHF personal radio: A theoretical and experimental study of characteristics and performance

A theoretical analysis of the characteristics of small personal radio antennas for the 68- to 470-MHz frequency range is given. Representing the human body by a simplified lossy dielectric structure, the influence of the body on the performance of the antenna is investigated in detail, and it is shown how antenna impedance, gain, and radiation patterns can be calculated taking the presence of the body into account. For very short antennas the results indicate that radiation from the body may dominate over the radiation contributed by the antenna itself, and that the presence of the body can increase the antenna efficiency considerably, indicating that even very short antennas may provide acceptable radiation efficiencies. The results of the theoretical work are supported by measurements on practical antennas. Quarter-wave and short antennas of the helical type are compared with respect to efficiency and radiation patterns at 80, 160, and 450 MHz, and it is demonstrated how the physical length of the antenna affects the antenna performance. The design of a very short and compact personal radio antenna is described.     

High-gain active composite right/left-handed leaky-wave antenna

A novel high-gain active composite right/left-handed (CRLH) metamaterial leaky-wave antenna (LWA) is presented. This antenna, which is designed to operate at broadside, is constituted by passive CRLH leaky-wave sections interconnected by amplifiers, which regenerate the power progressively leaked out of the structure in the radiation process in order to increase the effective aperture of the antenna and thereby its gain. The gain is further enhanced by a matching regeneration effect induced by the quasi-unilateral nature of the amplifiers. Both the cases of quasi-uniform and binomial field distributions, corresponding to maximum directivity and minimum side-lobe level, respectively, have been described. An active LWA prototype is demonstrated in transmission mode with a gain enhancement of 8.9 dB compared to its passive counterpart. The proposed antenna can attain an arbitrarily high gain by simple increase of the length of the structure, without penalty in terms of return loss and without requiring a complicated feeding network like conventional array antennas.     

Wiener-Hopf type analysis of dielectric-coated dipole antenna inrelatively dense medium

The problem of dielectric-coated dipole antennas in a relatively dense medium is solved using the Wiener-Hopf technique. The analysis is done for a perfectly conducting dipole antenna coated by a low-loss dielectric and embedded in a lossy medium of a wavenumber larger than that of the lossy coating. Analytic expression are derived for the input admittance and the current distribution along the dipole which is excited at the center across a nonzero width feed gap. Results are compared with available literature data for different antenna lengths embedded in an ambient medium with a loss tangent of σ/ω∈. The numerical work involves only the determination of certain integrals using standard integration routines     

Radiation from a generalized antenna in a stratified medium

Exact calculations are made of the electromagnetic field radiated by an arbitrary current distribution in an arbitrary stratified lossy medium. The medium thus characterized can include both a stratified earth and a many layer stratified ionosphere. The results of the investigation, which include the input resistance and the efficiency of the antenna, are useful for designing antennas in the ELF, VLF and LF bands. (The theory is applied to the case of an ELF-ring antenna.)     

Path loss model for wireless narrowband communication above flat phantom

A new empirical path loss model for wireless communication at 2.4 GHz above a flat, lossy medium, representing human tissue, is presented. The model is valid for dipole antennas for heights up to 5 cm above the phantom and for distances up to 40 cm, and was applied to muscle and brain simulating media. For antennas placed close to the lossy medium, it was found that antenna height has a major influence on path loss. The model has been validated by measurements and simulations, which show excellent agreement     

Social Spider Optimized Design Configuration of Multiband Reconfigurable Antenna for 5G Applications

Reconfigurable antennas receive more attention for many application due to their special characteristics like polarization diversity, multi band function and steerable diversity. However, reconfigurable antennas are capable of providing single and multiple reconfigurability. Nowadays, there is an increasing demand for multi-service radios for various spectrum standards. Many exiting works have been discussed about the enhancement of multi-band operation in reconfigurable antenna design. Most of them exhibit huge design complexity with high-cost consumption during the design optimization process. Thus, the proposed work uses Social Spider Algorithm for optimizing the design configuration of the reconfigurable antenna. Similarly, the band pass filter used at the feed line of the proposed antenna structure to easily achieve multi-band operation. The proposed design developed in ANSYS HFSS implementation platform and result analysis is performed in terms of bandwidth, VSWR, return loss, radiation pattern, gain, and directivity. The proposed reconfigurable antenna structure achieves 26.75 GHz bandwidth with 9.9 dB total gain and 8.8 dB directivity when comparing with existing works. Thus, the proposed antenna design suitable for 5G application applications by providing multi-band operation like WLAN, UWB, and Wi-Fi.

     

Electrically steerable passive array radiator (ESPAR) antennas

A novel ground-plane shape to improve the horizontal gain for electrically steerable passive array radiator (ESPAR) antennas is investigated. The peak directivity of a monopole antenna with a finite ground plane, such as a circular or rectangular ground plane is at a higher angle from the horizon. Thus, the horizontal gain is lower than that of a dipole antenna. Using a circular ground plane of a half-wavelength radius with a skirt of a quarter wavelength wound around it, the angle of the peak directivity and the horizontal gain for the ground-based communication system were improved. For an ESPAR antenna - one of the monopole arrays - the horizontal gain was also improved. It was confirmed that it was possible to form the main-beam radiation and a beam in the horizontal plane, each in an arbitrary direction, by changing the control voltage to the passive element. This was shown by an experiment with an ESPAR antenna with a finite reflector, a feed element, and seven passive elements.     

加载对拓结构介质的高增益Vivaldi天线

Vivaldi天线属于渐变缝隙天线的一种, 被广泛应用于平面超宽带天线设计中.Vivaldi天线在理论上可以展宽带宽到无限大, 但受限于加工工艺和尺寸, 其增益提高效果并不明显.文中立足于经典Vivaldi天线, 在天线辐射前端加载对拓结构的介质, 仿真结果表明相对带宽扩展了79.1%, 在5.5 GHz与12 GHz处提高增益达3 dBi.过孔矫正技术可以使天线辐射的相位分布更加均匀, 提高幅度分布的口径效率.在对拓结构基础上, 天线辐射端加载相位矫正的过孔阵列结构, 仿真结果表明加载该技术后, 天线提高增益2 dBi以上.包含以上两种技术的天线结构具有高增益、便于设计、小型化的特点, 这为端射天线提高增益和增强定向性提供了新的思路.     

A study of microstrip array antennas with the feed network

The radiation and losses in microstrip antennas with a corporate feed network are studied. A surface current approach is applied in which the electrical currents in the feed lines are modeled as in ideal transmission lines. The free-space radiation and the surface-wave excitation of typical segments in printed feed networks are studied. A four-element array antenna with its printed feed network is analyzed and predicted radiation patterns, directivity, and gain are presented and compared with experimental results. The gain and directivity of large arrays of 16, 64, 256 and 1024 elements are calculated and measurements in the frequency range of 10 to 35 GHz are reported