Design of a Compact Millimeter-Wave Microstrip Antenna with Wide Bandwidth and Broad Beamwidth

Design of a novel compact millimeter-wave microstrip antenna with wide bandwidth and broad beamwidth is presented. In the structure, multiple layers and a parasitic element as well as a coupling aperture are used to achieve wideband, while a conducting cylinder and the coupling aperture are used to obtain broad beamwidth. Finally, phased array with eight present elements has been designed as an example. Compared to traditional microstrip antennas and arrays, present antenna and array are of smaller dimension and broader beamwidth as well as wider bandwidth.     

Principles of space-time array processing for ultrawide-bandimpulse radar and radio communications

The emerging ultrawide-band (UWB) impulse technology has found numerous applications in the commercial as well as the military sector. The rapid technological advances have made it possible to implement (cost-effective, short-range) impulse radar and impulse-radio communication and localization systems. Array beamforming and space-time processing techniques promise further advancement in the operational capabilities of impulse radar and impulse-radio communications to achieve long-range coverage, high capacity and interference-free quality of reception. We introduce a realistic signal model for UWB impulse waveforms and develop the principles of space-time array processing based on the signal model. A space-time resolution function (STRF), a space-frequency distribution function (SFDF) and a monopulse-tracking signal are derived for impulse waveforms received by a self-steering array beamforming system. The directivity peak-power pattern and energy pattern of the beamformer are also derived. Computer plots of the STRF, SFDF and the beam patterns are obtained. The directivity beam patterns of impulse waveforms are sidelobe-free and, therefore, there is no need for sidelobe suppression via amplitude weighting of the array elements. Also, the resolution angle for the beam patterns is derived as a decreasing function of array size and frequency bandwidth. Electronic beamsteering based on slope processing of monopulse waveforms is described     

Rapid method for obtaining footprint patterns for very large antenna arrays

A new antenna pattern synthesis technique that allows the design of large planar antenna array radiating footprint patterns of a specified boundary with controlled ripple and sidelobe levels is presented. The method synthesises the desired footprint as a composition of a set of circular Taylor patterns appropriately weighted with the samples of the pattern obtained after stretching or shrinking a continuous circular aperture distribution developed by the Elliott-Stern method. A footprint of continental Europe radiated by a planar array with a large number of elements shows the technique's performance. The synthesis procedures were completed in about 1 s using a desktop computer.     

A comparison of time versus frequency domain antenna patterns

This paper compares the performance of antenna arrays that use sinusoidal and ultra-short pulse waveforms. There are two parts to the paper: first, a comparison of narrowband versus ultra-wideband linear arrays using an analytic approach and second, a series of computer simulations used to extend the analytic results and to show the characteristics of nonstandard array configurations. Analysis shows that antennas using ultra-short waveforms have highly desirable pattern properties that do not appreciably degrade under conditions of high array sparsity, failed elements, or antenna element position errors. Patterns are given that show these properties directly. These results are of particular importance to the emerging technology of base-band or time-domain communications and remote sensing. It addresses the practical problem of designing extremely large aperture space-based arrays without populating those arrays densely with antenna elements and also reducing the traditional fabrication tolerances.     

Analysis of phase-focused near-field testing for multiphase-centeradaptive radar systems

Airborne or spaceborne radar systems often require tests before deployment to verify how well the system detects targets and suppresses clutter and jammer signals. The radar antenna diameter can be large and thus the conventional far-field test distance is impractical to implement. The theory and simulations of phase-focused near-field testing for adaptive phased array antennas is discussed. With near-field source deployment, standard phased-array near-field phase focusing provides far-field adaptive nulling equivalent performance at a range distance of one aperture diameter from the adaptive antenna under test. Both main beam clutter sources and sidelobe jammer sources are addressed. The phased array antenna elements analyzed are one-half wavelength dipoles over the ground plane. Bandwidth, polarization, array mutual coupling, and finite array edge effects are taken into account. Numerical simulations of an adaptive antenna that has multiple displaced phase centers indicate that near-field and far-field testing can be equivalent     

圆口径正馈抛物面天线的近场分析

分析了圆口径正馈抛物面天线的近场.采用口径场绕射积分求取了天线的近场及远场方向图,绘制了波束宽度、方向性和最大副瓣电平三个关键参数随场点距离的关系曲线.通过与物理光学法的计算结果对比,验证了该方法的正确性.仿真结果是:随场点距离的减小,波束宽度展宽,方向性减小,最大副瓣电平在一定范围内波动.场点在D2/λ外,远场近似的波束宽度误差小于1%;在0.5D2/λ外,远场近似的波束宽度误差小于10%;在0.5D2/λ内,不能采用远场近似.     

Design of a Six-Sector Switched Parasitic Planar Array Using the Method of Genetic Algorithms

Switched parasitic planar arrays, as possible implementations of smart antennas, and an efficient method of designing them are presented in this paper. The radiation pattern of an array can be controlled by a digital word, the insertion of which in the antenna feeding circuit achieves electronic beam steering. The 1s and the 0s in the digital word represent the active and short-circuited elements in the array, respectively. The aim of the design is to cover the azimuth plane with six radiation patterns, each one having 3 dB beamwidth equal to 60° and relative sidelobe level not more than –3 dB. The well-known genetic algorithms are used tooptimize the antenna performance, determining the element positions and voltage phase values. This is made feasible by selecting the digital words, among the 2^N–1 available (N-number of elements), which maximize theobjective function containing the pattern requirements of the design. The numerical results presented show a possible application of this idea. An array of seven identical dipoles /2 offers diagrams, with an average 3 dB beamwidth equal to 63°. Relative sidelobe levels lower than –3 dB are obtained. Simulations at different frequencies prove that thearraydesigned here is a narrowband one and its bandwidth is 2.5% of the carrier frequency.     

有源相控阵天线瞬时宽带性能改善研究

采用无色散特性的模拟或数字移相器会导致天线波束指向随频率发生变化,即相控阵天线的孔径效应。工程上一般在子阵级别上采用色散特性的实时延迟线拓展相控阵天线瞬时带宽,但是子阵级延时量化误差会产生周期性栅瓣,导致天线副瓣性能恶化。文中提出在通道(或多通道收发组件)上设置小位延迟线、与子阵级大位延时线叠加使用,消除或改善子阵级延时误差造成的性能恶化。结合X波段有源二维阵列天线,对单元级、子阵级、子阵+单元两级三种情况进行了仿真。仿真结果表明,子阵+单元两级延时方法在扩展相控阵天线瞬时带宽的同时,能明显改善相控阵天线的副瓣特性,且具有较强的工程可实现性。     

A mathematical theory of antenna arrays with randomly spaced elements

Various probabilistic properties of a large antenna array with randomly spaced elements have been studied. It is found that for almost all cases of practical interest the required number of elements is closely related to the desired sidelobe level and is almost independent of the aperture dimension, the resolution (or the beamwidth) depends mainly on the aperture dimension, and the directive gain is proportional to the number of elements used if the average spacing is large. As a consequence the number of elements required is considerably less than that with uniform spacings. Starting with a given number of elements and a given aperture size, it is possible to improve the resolution by a factor of ten, a hundred, or more by spreading these elements over a larger aperture with little risk in obtaining a much higher sidelobe level and a lower directive gain. In fact, this method offers a solution which is optimum in a certain statistical sense, i.e., all sidelobes are of equal level with equal probability. In addition, this analysis also gives a simple estimate of the sidelobe level of most nonuniformly spaced antenna arrays. In a number of such arrays studied by various investigators with high speed computers, the agreement found is remarkable.     

Optical technique for broadbanding phased arrays

An optical method for broadbanding a phased array is considered. A narrow band feed-through aperture lens comprised of pick-up elements, radiating elements, and360degtype phase shifters is fed by a small feed array with an intervening passive lens. The lens has fixed frequency-sensitive properties. The feed array has variable time delay compensators which are selected in accordance with the desired scan angle in the far field. Using geometrical optics, design formulas are derived that relate bandwidth and scan angle to the minimum number of variable time delayers. To demonstrate performance, diffraction theory is used to calculate patterns, sidelobe levels, and efficiencies as a function of bandwidth and scan angle out to50degscan for several aperture sizes. In the worst cases, the optical system provides somewhat less gain than the comparable constrained subarray antenna; however, it always provides much better sidelobe levels.     

基于改进遗传算法的阵元失效校正方法

阵列天线中阵元失效,其方向图的副瓣电平会升高、主瓣变宽。保留遗传算法前期迭代的最优个体为新初始种群对遗传算法进行改进,以加快收敛速度和防止最佳染色体缺失。并利用基于优势保留的改进遗传算法,针对-40dB 的26 单元阵列,随机缺失3 单元后进行优化,恢复原方向图副瓣水平。结果表明,该算法能够有效减少阵元缺失后方向图的恶化。     

Multiple beam feed networks using an even number of beam ports

An aperture illumination compatible with the use of an even number of adjacent beam ports in a multiple beam feed network is discussed. The antenna pattern characteristics of near-in sidelobe levels, half-power beamwidth, aperture efficiency, and feed network loss are evaluated. Maximization of the available antenna gain at adjacent beam crossover points is shown to be possible for either sequential or simultaneons operation of a receiving system. The results presented indicate that lossy feed networks are quite suitable for certain array antenna applications.     

Minimization in variations of different parameters in different φ planes of a small-size concentric ring array antenna using firefly algorithm

The radiation pattern of a small-size concentric ring array antenna does not remain φ-symmetric, if the array is made with an appreciably lesser number of antenna elements. The sidelobe level, first null beamwidth (FNBW), half-power beamwidth (HPBW), and the null depths of the radiation pattern change significantly in different φ planes. An efficient pattern synthesis method has been developed in this work to reduce the variation of sidelobe level, FNBW, and HPBW of a small-size concentric ring array of isotropic antennas, for different φ cuts. It is done by finding out an optimum set of amplitude distribution of the array elements using firefly algorithm. The sidelobe level and the first null depth of the array are kept below a desired value for all the defined φ cuts. The directivity of the optimized array and the uniform array has been computed. The variation of all these parameters for different φ cuts has been compared to the same array with uniform excitation among the elements.     

用于超宽带高分辨率成像的二维稀疏MIMO面阵拓扑结构研究

分析并总结了超宽带二维多输入多输出(Multiple Input Multiple Output, MIMO)面阵拓扑结构设计的两条原则——等效孔径的均匀性与无明显遮蔽性, 并根据这两条原则提出了一种用于超宽带近距离高分辨率成像的新型面阵拓扑结构.与尺寸、阵元数相同的MIMO面阵相比, 该新型面阵结构在仿真获取的方向图中具有更好的聚焦效果和旁瓣抑制能力.并且, 不同距离下的聚焦结果显示, 该面阵的峰值旁瓣水平均要低于另两个阵列2 dB以上.对复杂目标成像的实验结果进一步证明了该阵列良好的成像性能.结合其等效阵元数量较少的特点, 文中提出的这种新型MIMO面阵拓扑结构为高效、实时的超宽带近距离高分辨率成像应用提供了可能.     

基于孔径长度域重采样的快速恒定束宽波束形成

为解决宽带阵列天线波束宽度抖动的问题,在分析阵元权系数和阵列方向图傅里叶变换关系的基础上,提出了一种基于孔径长度域重采样的快速恒定束宽宽带波束形成方法。该方法通过期望方向图的傅里叶反变换获取孔径长度域上的权系数曲线,然后用不同的采样间隔对该权系数曲线进行重采样得到不同频率下的阵元权系数。由于仅需进行一次积分运算,该方法具有运算量小、速度快的特点。为使阵列方向图在恒定束宽的基础上具有更好的方向性,通过对孔径长度域拟合度的分析给出了期望方向图的设计方法。仿真结果表明所提方法可以快速形成方向性较好的宽带阵列恒定束宽方向图。     

Minimum Sidelobe Levels for Linear Arrays

A method of finding the optimum sidelobe-minimizing weights for an arbitrary linear array is derived that holds for any scan direction, beamwidth, and type of antenna element used. Optimum linear array positions are then determined via the particle swarm optimization method. Hence, the two together can give a global bound on antenna array performance with regards to sidelobe minimization. Results are presented for linear arrays of 2-6 elements for different scan angles, beamwidths and antenna elements.     

Utilization of the lambda functions in the analysis and synthesis of monopulse antenna difference patterns

The properties of a general class of monopulse antenna difference patterns which are obtained by differentiating a desirable class of antenna sum patterns are analyzed. Their corresponding aperture distributions are synthesized using the Fourier transform. It is found that of the general class of patterns considered, there is one family which gives the best compromise between slope at boresight and sidelobe level. Curves are presented which relate sidelobe level and slope at boresight for this particular family; these curves may be used to design monopulse difference patterns for either a specified slope at boresight or a specified sidelobe level. Simple expressions for the corresponding far-field difference patterns, their beamwidth, and their aperture distributions are given.     

A Technique for the Synthesis of Line-Source Antenna Patterns Having Specified Sidelobe Behavior

A new method for the synthesis of line.source antenna patterns having prescribed sidelobe envelope functions is discussed. The patterns obtained are inherently nonsupergained and, in the sense of Taylor patterns, approach the narrowest beamwidth for the given sidelobe behavior. Sample patterns and corresponding aperture distributions, together with required design parameters, are given. The sidelobe envelope functions for those patterns having maximum gain for a given maximum sidelobe level are also presented.     

An aperture-coupled linear microstrip leaky-wave antenna array withtwo-dimensional dual-beam scanning capability

This paper describes an X-band 4×1 aperture-coupled series-fed electronically steerable microstrip leaky-wave antenna (LWA) array design, which has dual-beam radiation pattern and two-dimensional (2-D) beam-scanning capability. The LWA array is operated in the first higher order mode and excited by center-fed aperture coupled for dual-beam operation. The varactor-tuned phase shifters are placed between the antenna elements. The measured half-power beamwidth of the H-plane and quasi-E-plane radiation patterns are less than 30°. By tuning the reverse dc bias of the varactor diodes, the main beam can be scanned in azimuth plane from -13° to +13° off broadside. In the elevation plane, the beam-scanning angle is close to 20° as the operating frequency tuned from 11.58-12.5 GHz. Taking into account each phase-shifter insertion loss and phase progression, the measured results compared closely with the theoretical prediction. The proposed antenna array is suitable for wireless communication and collision warning radar systems     

一种串馈的非规则天线阵

均匀规则阵列天线的副瓣电平较差,且波束宽度较宽,不太适合于一维高精度相控阵雷达系统.针对这些要求,提出了一种基于串联馈电网络结构的非规则天线阵列.该阵列采用串馈方式,结合带空腔的微波多层板技术,通过带状线缝隙耦合方式,避免了背向辐射,同时获得宽带特性.该阵列采用遗传算法对阵列进行优化,获得低于-18 dB的理论副瓣电平,同时相比均匀规则阵而言,波束宽度仅有0.2°的拓宽.对于20°的波束宽度而言,该波束宽度扩宽量可以忽略不计.该阵列的实测2:1驻波带宽为19.8%,方向图带宽为12.2%,在方向图带宽内,阵列的实测副瓣电平低于-16 dB,阵列的带内测试增益高于11.7 dBi,实测结果和理论设计相吻合,表明该天线阵列适用于一维相控阵天线.