Design and development of a unit element microstrip antenna for aircraft collision avoidance system

Aircraft/traffic alert and collision avoidance system (ACAS/TCAS) is an airborne system which is designed to provide the service as a last defense equipment for avoiding mid-air collisions between the aircraft. In the existing system, four monopole stub-elements are used as ACAS directional antenna and one blade type element is used as ACAS omnidirectional antenna. The existing ACAS antenna has some drawbacks such as low gain, large beamwidth, frequency and beam tuning/scanning issues etc. Antenna issues like unwanted signals reception may create difficulties to identify the possible threats. In this paper, the focus is on the design and development of a unit element microstrip antenna which can be used for ACAS application and to overcome the possible limitations associated with the existing techniques. Two proposed antenna models are presented here, which are single feed and dual feed microstrip dual patch slotted antenna. These are designed and simulated in CST Microwave Studio tool. The performance and other antenna characteristics have been explored from the simulation results followed by the antenna fabrication and measurement. A good reflection coefficient, Voltage Standing Wave Ratio (VSWR), narrow beamwidth, perfect directional radiation pattern, high gain and directivity make this proposed antenna a good candidate for this application.     

Finding the approximate angular probability density function of wave arrival by using a directional antenna

The first-order approximate angular probability density function of wave arrival can be obtained by plotting the mean-square value of signal level versus the pointing angle of a mobile radio directional antenna during an entire test run. The accuracy of this first-order approximation is dependent on the beamwidth of the antenna. As the beamwidth of the antenna becomes narrower, the approximate density function becomes more accurate. There are also higher order approximations for obtaining a more accurate angular probability density function without narrowing the directional antenna beamwidth. These higher order approximations are related to the moments of the signal strength received by the same directional antenna used in obtaining the first-order approximation. All of these are theoretical predictions. An experimental verification using a first-order approximate angular probability density function in finding theoretical level crossing rates of a mobile radio signal is given. The theoretical level crossing rates are in fairly good agreement with the experimental ones as long as the angular probability density function is not far from a uniform distribution.     

Effect of Antenna Directivity on Angular Power Distribution at Mobile Terminal in Urban Macrocells: A Geometric Channel Modeling Approach

We present a geometric channel model to study the effect of antenna directivity on angular power distribution at the mobile terminal in urban macrocells. The methodology reviewed in this paper integrates the antenna effect into the model geometry, thereby facilitating a system-dependent channel characterization. As each device is limited in terms of measurement sensitivity, the effective scatterer distribution is essentially dependent on the antenna beam pattern. Subsequently, two heuristic rules are proposed to establish the underlying relationship between the model geometry and the corresponding wave-propagation processes. It is shown that the influence of directional antenna is twofold. First, it alters the spatial distribution of scatterers by providing a different sample space for the random field, and secondly, it distributes signal components into the angles-of-departure or collects them from the angles-of-arrival by weighted combination. Important channel parameters measured at the mobile terminal such as the angular power distribution, Doppler spectrum, and multipath shape factors are also investigated to further exemplify the usefulness of the proposed model.     

基于拓扑优化的微带天线奇异方向图设计

拓扑优化方法避免了结构的参数化扫描,直接优化材料排布,用于无源微波器件设计,可极大程度拓展设计解域。文中基于拓扑优化方法研究了微带天线的奇异辐射方向图设计。首先分析了具有奇异辐射方向图的伴随敏感度,其次构建了基于过渡边界条件的二维金属优化模型,再次提出了针对奇异辐射的多种目标场函数,分别实现了高增益定向指向波束、等幅双波束和任意方向线极化波束等奇异方向图。为验证算法有效性和准确性,最后加工并测试了具有高增益指向偏转方向图的微带天线,测试结果与拓扑优化结果吻合较好。此方法特别适合具有复杂目标的无源电磁器件设计。     

Novel small-size directional antenna for UWB WBAN/WPAN applications

This paper presents a novel small-size directional antenna design for ultrawide-band wireless body area networks/wireless personal area networks applications. The design is based on a typical slot antenna structure with an added reflector in order to achieve directionality. The effects of different antenna parameters and human body proximity on the radiation characteristics are analyzed. Antenna measurements with an optic RF setup were performed in order to characterize the small-size antenna far field radiation pattern. The different structural antenna parameters were optimized via extensive numerical simulations. Results show that for frequencies above 3.5 GHz, where the power front-to-back ratio of the directional antenna is greater than 10 dB, its impedance is nearly the same as in the free space. It is not the case neither for the omnidirectional slot antenna nor the monopole antenna next to the body. Between 3 and 6 GHz performance of the novel directional antenna, in terms of radiation efficiency and SAR values, is significantly improved compared to omnidirectional antenna designs.     

77 GHz汽车角雷达宽波束平坦增益阵列天线设计

设计了一款基于波束赋形技术的宽波束、平坦增益平面阵列天线,用于汽车角雷达系统.该阵列天线由三个1×10串馈线阵组成,串馈线阵采用单元不等间距分布的Dolph-Chebyshev天线综合法进行设计以降低副瓣.为了满足汽车角雷达宽视场角(field of view,FOV)的需求,对平面阵列天线采用波束赋形技术以展宽方位面...     

具有稳定相位中心的三馈点圆极化微带天线

介绍了一种具有稳定相位中心的圆极化微带天线。理论分析证明:采用幅度相等,相位相差120°的三馈电方式,圆形微带天线能获得圆极化辐射特性。中心对称的三馈点设计,天线可获得很高的相位中心稳定度。仿真结果显示:此天线相位中心的稳定度小于1mm.测试结果表明:在2.18～2.66GHz频带内该天线轴比小于3dB,相对带宽19.83%。     

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。     

An Alternative Setup for a Base-Station Cellular Antenna

This paper proposes the use of an alternative setup of a cellular base-station antenna with the potential of reducing the cochannel interference. The setup uses a different cell antenna placement strategy where there is one base-station antenna per cell located high at its center. Unlike a traditional base-station antenna radiating in the horizontal direction, the antenna under consideration radiates downward. The beamwidth of the antenna is considered to be wide enough to match the cell diameter. In addition, the radiation pattern beyond the associated beamwidth is assumed to possess a large attenuation. This paper studies the use of the proposed antenna setup by examining the cell geometry and grouping and its effect on the antenna radiation pattern. It is shown that for a sufficiently large attenuation pattern beyond the antenna beamwidth, the corresponding signal-to-interference ratio can be made significantly larger than the one resulting from the traditional antenna setup     

On the measurement of antenna beamwidth using extraterrestrial radio sources

The effect of source angular size on the measurement of antenna half-power beamwidth using extraterrestrial sources is analyzed for a circularly symmetric Gaussian antenna pattern and a circular uniform disk source. Results are presented in the form of universal curves which can be used conveniently in practical applications. The curves may be also used in the determination of the angular size of the disk source.     

Increasing the Azimuthal Resolution of Ocean Surface Currents for Dual-Frequency Radars

We describe an amplitude comparison scheme for increasing the azimuthal resolution of ocean suface current measurements using dual-frequency radar techniques. We show that an angular resolution of 4 percent of the antenna beamwidth can be acheived when the signal-to-noise ratio is 10 dB.     

Gain reductions due to scatter on wireless paths with directionalantennas

The use of a directional terminal antenna on a wireless link can enhance the received power by as much as the antenna gain. In local scattering, however, the enhancement will be smaller. We call this decrement the gain reduction factor, Δ. We present a statistical model of Δ for fixed suburban paths at 1.9 GHz, based on angle-of-arrival measurements in New Jersey. Our results address the influences of antenna height, antenna beamwidth, distance, and season     

Hybrid-coupled broadband triangular microstrip antennas

Two broadband configurations consisting of three hybrid-coupled equilateral and isosceles triangular microstrip antennas have been proposed. Both configurations yield more than four times the bandwidth as compared with the corresponding single triangular microstrip antenna. The radiation pattern of a hybrid-coupled isosceles triangular microstrip antenna is in the broadside direction with very small variation over the entire bandwidth. In addition, this antenna has wide half power beamwidth, making it suitable as an element for the large scan broadband antenna array.     

Antenna Effective Aperture Measurement With Backscattering Modulation

A scattering measurement method for antenna characterization is described. The antenna backscattering is modulated by an oscillator circuit. The modulation begins, when a known RF power is transferred to the oscillator circuit from the antenna. This enables the measurement of the effective aperture of the antenna, from which the antenna bandwidth and radiation pattern are obtained. A theory for antenna aperture measurement is developed using a simple circuit model for the antenna-oscillator system. A dipole and a PIFA with a reactive input impedance at the application frequency were measured. The antenna aperture was measured to an accuracy of 9%, and the measurements complied with simulated and measured references. The method provides simple and accurate bandwidth and radiation pattern measurements with the reactive load the antenna is designed to work with.     

支持空时分复用无线Mesh网络的微带阵列天线

支持空时分复用的无线Mesh网络采用多方向天线阵列技术,使用多个高增益定向天线进行多方向覆盖,具备通信距离远和天线自动扫描与对准的特性,便于快速部署。但现有的多方向天线阵列的设计从扩大通信距离的角度考虑,侧重于提高天线增益,使其垂直主瓣宽度仅为6°,这对于通信距离较近并且节点之间高程差较大的情况来说,覆盖性能不够理想。对多方向天线阵列的组成单元——微带阵列天线进行了优化设计,提出了一种支持空时分复用无线Mesh网络的微带阵列天线设计,其垂直主瓣宽度可达30°,并对设计的微带阵列天线进行了性能仿真和实际测试。     

应用定向天线测量无线信道角度功率谱

针对无线信道角度功率谱测量问题,提出了一种简单而新颖的测量方法.利用定向天线进行方位角扫描的功率测量,观测值、天线方向图和角度功率谱之间构成第一类Fredholm积分方程,通过求解积分方程可以得到角度功率谱.利用低通滤波器对观测数据进行预处理可以克服解积分方程的病态问题,改变滤波器参数并结合最小均方误差准则,可以得到角度功率谱的最小均方误差估计.仿真结果验证了该方法的有效性.     

Aperture-Sparsity Analysis of Ultrawideband Two-Dimensional Focused Array

We investigate the effects of aperture sparsity on the focusing performance and the angular-resolution capability of a two-dimensional focused array antenna excited by ultrawideband (UWB) impulse waveforms. The UWB-focusing array is characterized by a planar square aperture and a design parameter referred to as array spatial bandwidth. Spatial bandwidth is a function of the number of array elements, inter-element spacing, and frequency bandwidth. Performance analysis is carried out by generating computer plots of three-dimensional and two-dimensional antenna patterns for different values of array spatial bandwidth that hold for large aperture sparsity and large aperture density. The antenna patterns are peak-amplitude pattern, peak-power pattern, and energy pattern, whose narrow beamwidth and low sidelobe level are robust against aperture sparsity that may be caused by removed or failed elements. The half-power beamwidth (HPBW) of the antenna patterns, the focal distance, and the far-field distance of the UWB-focused array are expressed in terms of array spatial bandwidth. Computer simulation results show that UWB-focused-array beamforming based on impulse waveforms achieves efficient focusing of the radiation energy in the radiation-near-field region and beyond, and yields improvement in focusing performance and angular resolution for increased values of array spatial bandwidth. Such practical advantages are achieved without encountering grating lobes, large sidelobe level, or distortion of the radiation beam pattern that often limit the performance of the conventional narrowband phased array antennas.      

基于共形馈电网络的新型双频四臂螺旋天线

针对卫星地面手持终端系统对天线高效率宽波瓣的应用要求,文章提出一种新型双频印刷一体化四臂螺旋天线结构,通过两种方式提高其双频辐射效率:第一,每组辐射振子分成两个支路,分别以不同的长度、宽度和螺旋角度绕制以减少振子间耦合,同时覆盖两个不同的频点;第二,馈电网络和辐射振子进行一体化设计,提高其馈电效率。测试结果表明:在两个间距很近的频点(1.1倍频程)能够分别实现4.3dBi(低频)和4.2dBi(高频)的右旋圆极化增益,且4dBi以上右旋圆极化增益相对频带宽度分别为6%(低频)和5%(高频),圆极化3dB波瓣宽度均达到130°以上。该天线的双频点、宽波束、高效率性能适合于卫星通信手持终端系统应用。     

Optimal design of multiply fed dipole antennas

The gain of a mulitply fed dipole antenna of lengthL, small radiusaand arbitrary locations of feed voltages along the antenna is computed using the well-known moment method. An optimization routine is then employed to study the possibility of maximizing the gain in a specified angular direction and minimizing it at other directions for any given number of excitations and antenna length in order to determine the optimum complex values and location of each source. The results are presented in tables and graphs for a wide range of antenna length and number of feeds. It is shown that both the gain and beamwidth are improved by this technique at the expense of appearance of new sidelobes and requirement to design a more complicated feed network. The Fourier series expansion method is extended in order to determine the gain of a multiply fed wire antenna, and the results for the radiation pattern show good agreement with those based on the moment method.     

一种新颖可控陷波特性的超宽带天线

设计了一种具有可控陷波特性的超宽带天线,有效抑制了超宽带通信系统与窄带通信系统之间潜在的干扰。该天线的尺寸仅为3.5 cm×3.5 cm×0.1 cm,使用微带线进行馈电,并通过在天线单元上加载支节,从而实现天线可控陷波特性。利用仿真软件HFSS对天线进行计算,对天线的阻抗、方向图特性进行仿真对比。仿真结果表明,天线在超宽带系统3.1 GHz~25 GHz工作频段内的电压驻波比（VSWR）小于2,在5.2 GHz~5.8 GHz频率范围内的滤波特性较好,有效降低了无线局域网系统对超宽带系统的影响,在工作频段内该天线的辐射方向特性和方向图特性都较为理想。