分形天线的特性分析及其在MIMO天线中的应用

分形最基本的特征是自相似特性与分数维,可以很好地应用于设计天线.与传统天线相比,在性能保持相近的情况下,分形天线表现出两个突出的优势:减小天线尺寸和使天线在多频带下工作.文中以Koch天线、分形树天线和分形环天线为例,说明了分形天线减小天线尺寸的优势;以Sierpinski基垫天线为例,说明了分形天线增加天线工作频带的优势.还对Minkowski分形天线阵列进行了分析,表明作为天线阵列单元的分形天线,可以提高天线阵的辐射特性.文中提出了将Minkowski分形天线应用于多输入输出(MIMO)天线中.     

分形天线的IFS实现与特性分析

分形最基本的特征就是自相似特性与分数维，可以很好的用于设计天线。文章讲述了用IFS(迭代函数系统)实现分形天线的过程。并对一些典型的分形天线及分形天线阵列的特性进行了分析。     

一种高增益分形微带阵列天线

采用2阶皮亚诺分形曲线,设计了一种具有高增益端射特性的微带阵列天线。该阵列天线由多段皮亚诺分形曲线组成,通过添加微带相移器,分形曲线构成了一个偶极子天线阵列。文中介绍和分析了该分形阵列天线的工作原理、结构和主要参数对性能的影响。设计并制作了一只工作于5.8 GHz的分形阵列天线,仿真和测试结果表明,该天线具有良好的辐射特性,其端射增益达19 dB,旁瓣＜-12 dB,交叉极化＞30 dB,天线口径效率超过90%。     

分形理论在天线技术中的应用

文中针对分形的独特特征一自相似性（或自仿射性）和空间填充性，论述了将其运用于天线设计中。与传统的天线相比，在保持相同性能的条件下，这种天线有两个突出的优点：天线尺寸缩减和多频带性。文章还分析研究了分形几何在天线阵列设计中的应用，并探讨了分形理论在天线研究中的发展趋势和需要解决的问题。     

分形在天线雷达散射截面减缩中的应用

首次提出利用分形独特的填充性能实现天线雷达散射截面(RCS)减缩，同时，分形单元可以减缩单元间的耦合，提高阵列的性能。给出了分形天线与常规天线辐射、散射特性的对比，表明将分形的概念用于天线设计中，不仅可以减小互耦，提高天线阵列的辐射性能，而且也可以减小天线的雷达散射截面，对天线的隐身有一定的借鉴作用。     

用于天线设计的分形结构系统化生成法

提出一种分形结构的系统化生成方法,通过此方法可以系统化产生大量分形结构。这些分形结构可以用于分形天线/分形天线阵列的设计或其它分形结构的应用中。文中给出了以正方形为初始图形构造的多种分形几何图形,并给出了一些采用这些分形结构制成的分形贴片天线的实验结果。     

基于Weierstrass函数的分形天线阵辐射特性分析

分形天线是分形几何和天线技术交叉的产物,分形概念用于天线阵的工程合成,有助于将等幅度面阵和随机面阵的优点结合起来,将分形的自相似特征用于随机面阵设计有助于控制旁瓣区域的天线方向图。基于维尔斯特拉斯(Weierstrass)广义函数,研究天线阵排列系数函数的连续和不可微分的特性,通过对天线阵的分形电动力学和天线阵可实现性条件的研究分析,给出天线阵合成示例,得到Weierstrass不同尺寸天线阵的辐射特性与分形因子的作用关系。指出雷达天线阵列在结构、频带、副瓣等方面需要进行改进。     

精细结构对分形天线小型化的影响

为了了解分形技术中的精细结构在分形天线的小型化设计中,对分形天线小型化的影响状况,本文采用对比的方法,通过改变Koch分形单板子天线和普通单极子天线的结构参数,对比分析了不同的结构参数下天线上电流分布的仿真结果,得出的结论是精细结构的精细程度越精细,分形结构就能够进行越多次数的分形,分形天线小型化的程度也就越好.     

基于皮亚诺分形结构的微带阵列天线设计

为了适应现代无线通信对高增益宽频带天线的要求,改善微带天线增益低、带宽窄的缺陷,基于皮亚诺分形结构,设计研究一款工作在X波段的高增益、宽频带微带阵列天线。该天线由64个分形辐射单元组成辐射阵列来获得较高的增益,同时增加了寄生层形成F-P谐振腔,有效地提高了天线的带宽。仿真和测试结果表明,在10 GHz处天线的增益为24.1 d Bi,小于-10 d B的相对阻抗带宽达到了12.6%,同时天线的口径效率为89.4%。相对于传统的矩形结构,减小了天线的尺寸,实现了天线的小型化。     

基于分形的低副瓣天线阵列研究

通过对Cantor集线阵及其补集、同心圆环分形阵的阵列因子方向图特性的分析,指出大间距的分形阵列方向图具有高副瓣的缺点,提出了通过分形阵列阵元的锥削密度加权和少量大间距单元幅度加权相结合的方法来抑制副瓣,改善分形阵的方向图性能,给出了两种具有分形特点的高效率、低副瓣阵列形式和实际测试结果,为分形天线阵列的工程化应用提供了思路。     

Thinning of 2D and 3D Fractal Antenna Arrays with Bounded and Unbounded Fractal Distribution Functions for Celestial Communications

Fractal antenna arrays are geometry‐based thinned arrays having multiband applications. The major challenge of these arrays is their large number of elements at higher expansion factors. This article presents the thinning of fractal antenna arrays while maintaining an appropriate balance between the side lobe level and beam width by using various quantized fractal distribution functions. A 2D square fractal antenna array and 3DSierpinski gasket antenna array are considered in this article to validate the proposed distribution functions. Nearly one third of the antenna elements are thinned in each successive iteration except in the case of a one‐count distribution function. The proposed technique can simplify practical implementation and exhibits better performance for various parameters such as the side lobe level, side lobe angle, and half power beam width than fully populated fractal antenna arrays.     

基于矩量法的分形环八木天线的特性分析

八木天线是一种常用的天线形式.本文将Minkowski分形环应用于八木天线设计中,利用分形结构的空间填充特性来减小天线的横向尺寸,从而实现天线小型化设计.设计了工作于880～960MHz的6元二阶Minkowski分形环八木天线,以矩量法为核心对设计天线进行数值分析,将线天线模拟为细带线模型,天线表面采用三角单元进行剖分,RwG基函数作为电流展开函数.同方环八木天线进行了比较,在驻波特性、辐射特性相似情况下,分形环八木天线的尺寸缩减了29.8%.     

A fractal metamaterial based printed dipoles on a nickel oxide polymer palm fiber substrate for Wi-Fi applications

In this paper, a novel antenna circuit based metamaterial (MTM) structures is proposed for Wi-Fi applications. The antenna consists of two dipoles with 3 × 5 Hilbert-shaped MTM array printed with Sliver Nanoparticles Conductive Ink (SNPCI). The antenna substrate is mainly created from INP composite of: Iraqi Palm Tree Remnants (IPTR) and Nickel Oxide Nanoparticles (NONP) with Polyethylene (PE) mixture. The relative permittivity (ε_r) and permeability (μ_r) are measured using an open-stub microstrip resonator to find ε_r = 3.106 − j0.0314 and μ_r = 1.548 − j0.0907 at the frequency band of interest. Numerically, Finite Integral Technique (FIT) and Finite Element Method (FEM) of CSTMWS and HFSS formulations, respectively, are invoked to investigate the antenna performance. Experimentally, the antenna exhibits two resonances, |S₁₁| < −10 dB, at 2.45 GHz and 5.8 GHz with gain of 2.6 dBi and 4.8 dBi, respectively. The antenna shows a bandwidth of 500 MHz around the first resonance and 2 GHz at the second resonance. The measured radiation patterns at the two resonances are found to be mainly directed toward the antenna end fire with radiation efficiency of 0.8 and 0.65 at the first and second modes, respectively. Finally, the proposed antenna performance is compared against a reference antenna to reveal the excellent enhancements.     

Miniaturization of microstrip loop antenna for wireless applications based on metamaterial metasurface

The metamaterial and fractal techniques are two main methods for antenna miniaturization and in this paper, we have modeled an especial shape of the antenna based on loop formation with metamaterial load for this aim. The metamaterial layer is made by multi parallel rings and the result shows that the final antenna size reduced drastically while the frequency shifts from 7 to 4 GHz. The antenna has Omni-directional pattern with the gain of 3.5 dBi, so the size is reduced around 40%for 4.5 GHz and another resonance is made at 2.5 GHz with a return lossless than −6 dB with more than 60% frequency shift. The reflection and transmission have been utilized for showing the left hand characteristic based on two port periodic simulations in HFSS full wave software. We show that how the metamaterial load can provide the circular polarization (CP) by controlling the current distribution. We also presented that by making slots we obtained the better Axial Ratio (AR) and miniaturized the antenna with reconfigurable qualification. As a result of fact, we show that by using metasurface we able to miniaturized the antenna and simultaneously achieved the circular polarization.     

Microstrip Sierpinski fractal carpet for slot antenna with metamaterial loads for dual-band wireless application

The compact microstrip antennas with the dual-band characteristic and reconfigurable qualification have been noticed and investigated in this paper. We have developed the slot microstrip antenna with Sierpinski carpet and Minkowski formations and then the metamaterial loads are placed on this antenna in the slot area. The reflection/transmission method has considered to obtain the permittivity and permeability of the split ring resonator (SRR) as a metamaterial. Finally, we show that by using some junction in the metamaterial layer, we can obtain reconfigurable characteristic. Both antennas have dual-band characteristic where the first antenna has two resonances at 3.2 and 4.5 GHz and in the second antenna by altering the metamaterial layer both resonances are occurring at 3.5 and 5.8 GHz. We show that the antenna has two resonance frequencies that matched with the metamaterial Double Negative (DNG) characteristic. Both antennas are printed on FR-4 also we compared measurement and simulation results together. Aforementioned antennas cover the main wireless, WiMAX and LTE bands with sufficient gain and high efficiency (more than 80% typically) with a bi-directional radiation pattern for the indoor application. Here, the metamaterial is used for controlling the resonances and Sierpinski carpet is developed for matching.     

分形开槽减缩微带天线RCS

分形由于其独特的结构及性能早已在天线的设计中有所应用,但较少地应用于天线雷达散射截面减缩。本文首次将分形思想应用到开槽微带天线中。设计了一副分形开槽微带天线,与常规微带天线相比,在辐射性能降低不多的同时较好地实现了整个频带RCS减缩。     

一种新颖的树状分形超宽带天线

该文设计一种新颖的树状分形超宽带天线,该天线采用梯形结构的有限接地面。增加树状分形结构的迭代次数和优化有限接地面的形状可以使天线获得良好的阻抗匹配,进而实现天线的超宽带性能。该天线的工作频带为4.2~17.5 GHz(相对带宽为122.6%),天线的电尺寸为0.350.35,可应用于C波段、X波段、Ku波段和超宽带(UWB)波段通信,具有广泛的应用前景。实测结果和仿真结果吻合,证明了该天线的有效性。     

一种新型共边矩形环嵌套的分形多频天线设计

提出了一种新型分形结构的天线,该分形结构由多个共用一条边的矩形环嵌套构成。由于结构的自相似特性,使天线能够在多个频段工作。研究表明,天线的通频带个数由分形结构的矩形环个数控制,且各谐振频点与相应辐射单元的尺寸密切相关。设计了能同时工作在蓝牙、WLAN和WiMAX频段的三频天线,天线仿真的谐振频点分别为2.44GHz、3.55GHz和5.59GHz,相应的带宽分别为7.0%(2.35GHz-2.52GHz)、15.0%(3.28GHz-3.81GHz)和30.1%(5.13GHz-6.95GHz)。实物的测试结果与仿真结果基本吻合,符合设计要求。