一种新型分形微带天线的仿真优化

研究分形微带天线优化问题,针对多频通信需求,要求回波损耗特性实现多频性。传统分形天线结构单一、多频性能差。为了改善其多频特性,利用Cantor集和Koch曲线原理,通过建立不同宽度和长度的导带模型,并将导带宽度较窄的短截线替换为Koch曲线,提出了一种新型的适合TD-SCDMA、WiMax及WLAN的无线通信的三频段分形微带天线。利用CST软件进行仿真,得到了天线仿真回波损耗及方向图,并实测了回波损耗,实测结果与软件仿真结果吻合较好。经实验证明,所设计的天线能很好满足多频通信的需求。     

一种基于分形结构的超宽带天线研究

基于微带天线和分形天线的基本理论,采用正方形和圆形交替的方法设计了用于超宽带（UWB）通信的分形天线。利用电磁仿真软件CST软件对所设计的天线进行仿真、优化,并分析了影响天线阻抗特性和辐射特性的关键参数。从仿真实验结果可以看出,所设计的天线有较好的全向辐射特性和宽的阻抗带宽,能够满足超宽带通信需求。     

基于规范子块五点和的快速分形图像编码

分形图像编码通常需要较长的时间,编码时间主要花费于在一个海量码本中搜索每个输入子块的最佳匹配块.针对这个问题,提出一个限制搜索空间的算法.它主要基于图像块的一种新特征——五点和,把搜索范围限制在初始匹配块(五点和意义下与输入R块最接近的D块)的邻域内.实验表明：该算法能够大大减少子块匹配比较的数量,与基于叉迹的快速分形算法比较,在相同的搜索邻域内,在编码时间、图像质量和压缩比方面都更优.     

一种改进的分形优化算法

分形算法是一种全局优化算法,通过对可行域的嵌套分割来完成搜寻过程,由于其深度优先的搜索策略,开始容易陷入局部最优,收敛速度慢。针对原算法的缺点,提出一种改进的分形优化算法。该算法模拟分形生长的过程,避免了对可行域的盲目分割,并指导新点以较大的概率产生于较优的区域。通过数值试验来验证该算法的有效性,结果表明该算法具有良好的收敛性。     

一种基于分形的关键帧算法研究

提出了一种基于分形的关键帧算法,算法对初始关键帧和终止关键帧之间的压缩映射的对应准则和概率的对应准则各给出了一种较好的解决方法.实验结果表明,算法产生的动画过渡平滑,节奏自然,画面流畅,本文算法的主要特征是它能处理传统的关键帧算法所不能处理的分形物体,在实际应用中,该算法能够在提高制作效率和中间帧质量的同时大大减少动画制作的成本.     

一种基于Markov矩阵的分形建模方法

提出一种基于转移概率矩阵的Markov迭代函数系统分形吸引子的建模方法.将MIFS的仿射变换实施多级化的分解,利用转移概率矩阵对吸引子的局部子图像做Markov变形处理,基于计算机数学实验给出了雪花分形和树木分形的应用实例,表明该方法能够有效地控制分形吸引子的局部变形.     

一种双陷波超宽带微带天线

设计了一种结构简单且具有良好工作性能的双陷波超宽带微带天线。通过采用缺陷地和阻抗变换结构设计了具有超宽带工作特点的五边形微带天线结构,满足VSWR≤2的频带覆盖3.1 GHz～10.6 GHz;分别在辐射贴片和馈线上嵌入矩形窄缝和U形窄缝结构,实现WLAN频段(5.15 GHz～5.85 GHz)和X波段通信下行频段(7.25 GHz～7. 75 GHz)陷波工作性能,其他工作频段内具有良好的辐射特性。实测结果和仿真数据吻合较好,验证了设计的正确性。     

一种共面波导馈电的分形缝隙宽带天线

结合共面波导馈电和分形天线的优点,设计了一种共面波导馈电的正六边形分形缝隙天线。选择正六边形分形缝隙结构,采用渐变的共面波导馈电,不仅拓宽了阻抗带宽,而且实现了天线的小型化。通过计算测量,对天线的阻抗特性、增益和方向图进行了研究。实验表明,此分形缝隙天线的阻抗带宽达到89%,并且在整个工作频段内具有良好的辐射方向特性。     

三频段高稳定辐射分裂生长式分形微带天线

针对移动通信及射频识别等多应用频段覆盖的需求,提出一种新型分裂生长式分形结构,利用π型四边形雪花结构进行分裂生长式迭代算法,实现了高度集成的等效复合辐射边,研制了一款分裂生长式分形微带天线,能够同时覆盖移动通信的900 MHz频段、1.9 GHz频段和射频识别的2.45 GHz频段,3个工作频带的回波损耗最小值都低于-20 d B,工作带宽都大于0.2 GHz,天线在3个工作频段都具有高稳定辐射特性。该天线成功实现了移动通信系统和射频识别多体系兼容,有望用于通信及远程身份识别及支付体系。     

Analysis of a microstrip antenna with fractal multilayer substrate using iterative method

A microstrip antenna with fractal multilayer substrates is studied by using an iterative method based on the concept of waves. A two‐dimensional fast Fourier transformation algorithm is introduced to simplify calculations and accelerate the convergence with reduced central processing unit time. Good agreements are obtained with already published results on fractal antenna. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 212–218, 2001.     

A novel dual‐wideband inscribed hexagonal fractal slotted microstrip antenna for C‐ and X‐band applications

This paper presents a novel geometry of inscribed hexagonal slotted microstrip antenna for dual‐band performance where the fractal iteration has been made by introducing concentric slots in the patch geometry. Using the equivalence principle and cavity model, the basic geometry of the hexagonal slotted patch is analyzed, and the resonant frequencies of different modes of the patch are computed. Higher‐order modes of the patch antenna are used to obtain dual band. Good performance in terms of the reflection coefficient is proved with the help of parametric analysis. The antenna geometry is simulated using electromagnetic simulation software based on the finite‐element method. The prototype of this antenna is fabricated and tested. The practical results match with the simulated results. The proposed antenna provides improved average gain. The peak values of measured gain are found to be 5.238 and 7.023 dBi—in the two bands 5.85 to 6.48 GHz and 7.28 to 8.63 GHz, respectively. Stable radiation patterns with good average gain make the proposed antenna appropriate for long‐range transmission. Furthermore, low profile and low cost make this antenna suitable for the future point‐to‐point high‐speed wireless communication applications.     

Direct and electromagnetically coupled compact microstrip antenna design with modified fractal DGS

This article proposes ultra‐miniature microstrip patches with direct and electromagnetically coupled feeding mechanism for wireless communications at 10 GHz. Antenna size reduction is achieved here by loading a modified Minkowski fractal (type‐2) defected ground structure (MFDGS‐II) exactly beneath the radiating patch. The proposed method involves the selection of best DGS configuration through sensitivity analysis of the antenna structure. From different applications point of view, three different designs: a single layer direct fed patch and two electromagnetically coupled fed multi‐layered microstrip patch antennas are proposed here and designed with MFDGS‐II. The resonant frequencies of the antenna designs are reduced in a significant manner incorporating MFDGS‐II without any change in the physical size of the antenna. The prototypes of the proposed antennas are fabricated, and the performance parameters are measured. Compared with other existing structures, with a lower patch size of 0.20 λ₀ × 0.15 λ₀, the proposed single layered antenna with microstrip feed achieves a patch size reduction up to 67% and an overall volumetric reduction of 84%, respectively. Similarly, the proposed multi‐layered patch with proximity feed exhibits a maximum impedance bandwidth of 600 MHz and the aperture coupled fed patch has a realized gain of 6.2 dBi with radiation efficiency of 91% centered at 10 GHz. All three proposed compact antenna structures are best in three different aspects and have the potential to meet the practical requirements for X‐band portable wireless applications.     

一种应用于微波探测的双频天线的设计

为增加火灾探测天线频带范围,基于微带贴片天线,采用凹槽加载技术,设计了中心频率在Ku(12.4～18.0 GHz)波段的双频微带单元天线.利用HFSS软件对其建模、仿真及优化,结果表明,该单元天线在14.8 GHz和16.1 GHz时回波损失达到最小值,且回波损失小于-10 dB的带宽分别为600MHz和390 MHz.利用该单元天线,进而设计了一款2×2阵列天线,实测结果表明:该阵列天线具有很好的双频谐振特性,在14.3～14.9 GHz和15.7 ～16.1 GHz频带内既保留了原单元天线好的回波损耗特性,又提高了增益,使两个频段最大增益分别达到13.7 dBi和11.3 dBi.     

倒置卡塞格伦天线抛物面以及馈源的设计

研究了倒置卡塞格伦天线的抛物面以及馈源,并采用FEKO进行仿真优化,设计了工作在8~9GHz的倒置卡塞格伦天线的抛物面以及馈源,给出了抛物面参数的选择方法以及馈源的尺寸。     

Bacterial foraging optimization technique to calculate resonant frequency of rectangular microstrip antenna

Resonant frequency of rectangular microstrip antenna having various substrate thicknesses are generally calculated using the standard expressions presented in literatures. But these equations suffer from errors when compared with the experimental values due to Quasi‐TEM propagation in the microstrip structure and fringing field. A number of researchers used soft computing approach such as neural networks and genetic algorithm on those equations to minimize the error for better accuracy. Bacterial foraging, an evolutionary optimization technique conceived in recent times, has many advantages over genetic algorithm and is yet to be applied on the design of microstrip patch antenna. In this article, a novel technique is developed to apply bacterial foraging optimization technique in conjunction with the expressions developed to calculate accurately the resonant frequency of rectangular microstrip antenna of any dimension and of any substrate thickness. Further, bacterial foraging is applied to the calculatation of the feed point of microstrip antenna. The technique developed in this article can be a generalized soft computing tool to calculate resonant frequency of rectangular microstrip antenna. Similarly, the idea of the article can be used for calculating the various parameters of microstrip antennas of different structure and geometry. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

A T‐type fractal boundary single‐feed circularly polarized microstrip antenna

A single‐feed T‐type fractal boundary microstrip antenna is presented. It is established that a very good circular polarization is realizable with 3‐dB axial ratio bandwidth of 1.27% at the center frequency of 2446 MHz by changing the electrical length in two directions of the square patch by using T‐type fractal curve as boundary. Further it is shown that the surface area occupied by the antenna is reduced compared to the Euclidean shaped patch antenna without much degradation in gain of the antenna. Experimental results are compared with simulated results and a very good agreement is obtained. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

基于分形理论对天线的讨论

利用分形理论设计出的分形天线和分形天线阵,具有小巧、灵活、轻便、同时还具有多频带、宽频带和“自加载”特性,它们存在多种多样形式,在军事工业和通信行业将有很大的发展潜力。     

汽车雷达微带阵列天线设计

为提高汽车雷达性能,设计了一款汽车雷达天线,采用4×8微带阵列天线形式,设计中心频率为24.1 GHz,采用指数加权的方式设计馈电网络,以降低副瓣.在HFSS电磁仿真平台上对其进行仿真、优化.仿真结果显示天线最大增益为21.4 dBi,副瓣电平低于-15 dB,H面半功率波束宽度约为10°,在24 ～ 24.5 GHz频段性能稳定.天线整体长约70 mm,宽约36 mm,体积小.将该天线应用于汽车雷达可以探测车辆和障碍物的速度、距离、角度等信息,从而实现防撞预警、盲点侦测等功能.