Adaptive crossed dipole antennas using a genetic algorithm

Antenna misalignment in a mobile wireless communications system results in a signal loss due to a decrease in antenna directivity and a polarization mismatch. A genetic algorithm (GA) is used to adaptively alter the polarization and directivity of a crossed dipole receive antenna in order to increase the link budget. The three orthogonal dipole configuration works better than only two crossed dipoles, but both improved the link loss as the angular pointing errors increased. A GA with a high mutation rate works best for a noiseless open loop adaptation, while a GA with a low mutation rate works best for noisy fully adaptive system.     

Design and Prototyping of a Switching Beam Disc Antenna for Wideband Communications

The design procedure for a switching beam antenna for wireless communication systems is given. The antenna can rotate the beam over the whole azimuthal angle exploiting its geometrical and electrical cylindrical symmetry. The required directivity and the beam rotation are provided by a sequential insertion of metallic posts into the radial waveguide that forms the main body of the antenna. The first stage of the design involves setting up the dimensions of an omnidirectional antenna, to which the desired directivity is subsequently provided. After optimization to maximize the impedance bandwidth, the final antenna was prototyped. A comparison between simulated results and experimental data is presented     

基于极化二元阵雷达的空域虚拟极化滤波算法

极化滤波利用干扰信号和目标信号的极化状态差异,可有效抑制有源压制干扰,然而,现有极化雷达需要两路发射通道和接收通道,存在系统复杂、实现代价高等诸多困难。该文提出了一种新体制极化雷达模型极化二元阵雷达,该系统仅需一路发射通道和接收通道即可实现极化测量。基于极化二元阵天线的空域极化特性,建立了有源压制干扰、目标回波的接收信号模型,研究了抑制有源压制干扰的空域虚拟极化滤波算法,仿真实验结果表明:对于窄带噪声调频干扰,信干比(SIR)改善因子能达到20 dB以上。     

Reactively Steered Ring Antenna Array for Automotive Application

A novel type of smart antenna, called a reactively steered ring antenna array (RSRAA), is proposed. The antenna features a conformal configuration with three overlapping one-wavelength ring elements. Directivity can be controlled by changing the values of variable reactance circuits that are embedded in the antenna. The antenna can be mounted on the windshield of an automobile without interfering with the view of the driver. An equivalent model of six dipole elements is derived from the original antenna configuration to enable simple calculation of directivity when a set of reactance values is given. The validity of the proposed equivalent model is confirmed by comparing simulation results calculated by the equivalent model and by the method of moments. Another simulation shows that the conventional reactance domain multiple signal classification algorithm can be applied to the proposed antenna while keeping the estimated direction-of-arrival number equal to the number of reactance circuits. In addition, the characteristics of an RSRAA, which is optimized at 2.4 GHz and is mounted on an automobile, are measured in an anechoic chamber, and directivity control is found to be implemented effectively.     

Analysis of higher order regular polygonal loop antennas

Higher order regular polygonal loop antennas are analyzed. The input impedance of higher order antennas varies gradually when the operating frequency or the order of polygon changes. This behavior of input impedance provides a wide range of input impedance and many resonant points to antenna designers. The higher order regular polygonal loop antenna generally possesses higher directivity but poorer broadband impedance property. As the operating frequency becomes higher its directivity increases remarkably and the broadband property becomes more prominent. To achieve the desired properties one may select one of the many design data sets with a trade-off between broadband property and directivity     

基于延迟自相关双门限的短波天线选择方法

短波固定台站配有多副发信天线,在实际应用时,一般是根据预先方案选择一副天线发射信号,没有充分利用天线的方向性,因而通信效果并不是最佳.针对这一问题,设计了一种能够在收发双方进行天线发送信号质量评估的探测机制,通过基于延迟自相关运算的双门限检测技术,在收接端判决各发信天线探测信号质量,然后根据评估分值,从短波固定台站众多的天线中自动选择通信效果最佳的发信天线发射信号,在不改变现有配置的情况下最大限度地提升通信质量.仿真结果表明,该方法可行有效,能够以较小的代价提高天线选择效率,充分利用天线的方向性,达到提升发射效率和通信效果的目的.     

基于定标体散射特性的天线极化特性的测量

天线的极化特性是描述天线性能的重要参数,是雷达目标特性测量领域的基础性问题,对于实际的雷达天线而言,其极化特性的外场测量是一项复杂而又艰巨的工作。文章提出了一种基于定标体散射特性的天线极化特性的测量处理方法,建立了雷达波束扫描定标体的接收回波模型,可实现对线极化和圆极化天线极化特性的测量,给出了外场实验布局和测量步骤,实测数据和仿真实验证明了该方法的可行性。该方法能够有效地减少设备量和降低测量成本,提高雷达远场的逼真度。     

A New Dielectric Grating Antenna with Large Leakage Constant for Millimeter-Wave Applications

The leakage properties of a new dielectric grating leaky wave antenna are carefully examined by an approach of combining the multimode network theory with the mode-matching method. A systematic comparison is given for the leaky characteristics of the n?=??1 space harmonic of TM mode polarization between the present antenna and the traditional one. It has been found that the former is not only of lower conductor loss, but also of larger leakage constant than the latter. As a result, the dimension of the antenna could be largely reduced, which is of practical significance for some applications. Extensive numerical results of the radiation characteristics are given to establish useful guidelines for the design of the new grating antenna. Furthermore, special features such as cancellation or resonance effects are high-lighted and discussed. Physical insights for the mathematical findings are also presented.     

Reduction of wireless signals in indoor environments by using an active frequency selective wall based on spectrum sensing

This paper presents a wireless local area network (WLAN) spectrum control system that uses active frequency selective shielding walls to selectively reduce or pass WLAN signals in the 5 GHz band indoors. The proposed system utilizes a well‐known active frequency selective structure based on a rectangular loop with PIN diodes and is thus capable of either reducing or passing the WLAN frequency by using the on/off switching of the PIN diode based on the measured electric field strength in indoor. We designed and simulated the proposed active frequency selective shielding wallpaper by using commercial electromagnetic simulation software and confirmed that the proposed structure can reduce the WLAN signal by switching the PIN diode by applying the manufactured prototype on the exterior of an experimental apparatus containing a WLAN receiver antenna that is capable of measuring the received electric field strength. Extension of the results presented herein can be applied to reduce the wireless signal to enhance the spectrum efficiency of an indoor space.     

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。     

基于和差波束极化特性的目标极化散射矩阵测量方法研究

该文建立了一种基于常规单脉冲体制的目标全极化散射矩阵测量算法。首先证明了该型雷达天线具有复杂的极化结构,并且对回波信号的极化特性有一定的敏感性。利用单脉冲雷达和差通道的极化特性在获取目标角度信息的同时利用一个脉冲重复周期即可完成目标极化散射矩阵的测量,降低了全极化单脉冲雷达研发的系统复杂度和设计成本,通过电磁计算和仿真分析验证了上述研究的正确性。这对于开发现有雷达装备的极化测量处理能力、提升其抗干扰和目标识别能力具有一定的启发和指导意义。     

Effects of polarization, antenna directivity, and room size ondelay spread in LOS indoor radio channel

This paper presents results of experiment and computer simulation based on a three-dimensional (3-D) ray-tracing method for various directional polarized antennas, where the effects of polarization, antenna directivity, and room size on delay spread (measured at 94 GHz) are investigated in the line-of-sight (LOS) indoor channel. These results indicate that the delay spread can be reduced significantly by the directional circularly polarized antenna. It is also found that the delay spread increases almost proportionally with the square root of the room floor area     

散射矩阵同时测量的一种新方法

该文提出了散射矩阵同时测量的一种新方法频域分割法。这种方法的基本原理是:发射时水平极化天线和垂直极化天线同时发射两个中心频率不同、调频斜率相同的线性调频信号,中心频率的差值等于或略大于信号带宽,接收时上述的两个天线同时接收,那么每个天线接收的回波是两个不同极化组合回波的叠加,我们利用两个回波信号频谱的差异,将之分离,从而实现散射矩阵的同时测量。这种方法避免了测量不同时以及极化开关造成的极化耦合而引起的测量误差,与散射矩阵同时测量的信号编码法相比,更容易实现高极化隔离度。     

Physical limitations on interference reduction by antenna pattern shaping

The problem of minimizing the signals received from interfering or undesirable signal sources by appropriately modifying the antenna radiation pattern is addressed. The solution is presented in terms of the modal expansions of the monochromatic electromagnetic fields outside the radiating structure, and appropriate optimization of these radiation patterns. Physical realizability of the results is assured by requiring that the allowable fields are derived from nonsuper gain antenna excitations; hence the results represent an upper bound on the performance. We consider two complementary, one-dimensional antenna structures, i.e., a circumferentially symmetric line source of lengtha, and an axially independent cylindrical antenna of radiusrho_{0}. We consider first the case ofNdiscrete interfering signals and compute the loss in antenna directivity when the radiation pattern is modified so as to place a null at each angular position of the interfering signal sources. The results indicate that if all interfering signals are located outside the main beam, the loss in directivity is negligible. When one or more undesired signal sources are in the main beam, the antenna directivity will be reduced appreciably. It is shown that when uniformly distributed noise is superimposed over the discretely located interfering signals, the same antenna pattern maximizes the signal/noise ratio for those practical cases when the interfering signal power is significantly greater than the uniformly distributed noise source power. It is further shown that introducing noise uniformly distributed over all space is equivalent to adding thermal noise at the antenna terminals, as would occur with the receiver. Finally, the effects of bandwidth on the system performance are considered.     

MF AM folded monopole characteristics

Folded monopole antennas have been used for many years in medium frequency amplitude modulation broadcast applications. These antennas offer a grounded radiating structure with a height approximating a quarter wavelength. Folded monopoles have been studied exhaustively during a previous effort in an attempt to characterize the input impedance and directivity characteristics as a function of monopole height. As a result it was observed that several impedance regions can be achieved as a function of antenna height and cage diameter: Some of these regions permit a bandwidth operation sufficiently broad to support a high fidelity response for analog or digital transmissions. This type of antenna can be useful at different heights including a self matching region at the standard 50 ohms impedance. By choosing the appropriate antenna physical dimensions, antenna tuners can be avoided and thus it increases efficiency. Measurements have been made on a full scale 72 meter tower with a 6 wire cage in order to validate the calculated antenna input impedance and directivity. The cage and supporting mast make up the equivalent of a transmission line. For this reason different standard triangular towers were analyzed in order to determine their effect on the input impedance. Tower effective radius is determined taking into account the tower width and the tower leg diameter. At the same time, a minimum antenna height with maximum efficiency has been analyzed to solve the hard problem for installations at places where antenna height is a challenge for the designer.     

低副瓣气象雷达天线增益测量及误差分析

简述了低副瓣S波段8.54 m气象雷达天线的基本特性,提出利用方向图积分法计算天线方向性增益,扣除方向图有限积分区域引起的增益损失、漏失损失、交叉极化损失、失配损失和馈源网络插入损耗,从而确定天线增益的方法。给出了各种增益损失因子的计算公式,分析了方向图积分法测量天线增益误差,其均方根误差≤"0.224 dB。最后给出了S波段8.54 m气象雷达天线增益的实测结果,测量结果同理论结果吻合很好。     

探针馈电印刷线天线的矩量法分析——（Ⅰ）单臂天线

利用同轴内导体延和为探针对印刷天线进行直接馈电是一种易于实现的馈电方式。本文介绍了一种分析单臂探针馈电印刷线天线的数值方法,该方法是基于并矢格林函数和互易定量求解电流积分方程的矩量法,适合于分析任意形状印刷线天线,首先给出描述电流分布的积分方程及其矩量法求解公式,在解得电流分布基础上,应用驻相法计算远区辐射场,通过计算与实验比较,验证了分析方法和计算程序的正确性,最后对一圆极化开口印刷圆环天线进行分析计算,表明了方法的实用价值。     

一种基于光子带隙结构的新型圆极化天线

分析了一种畸变式共面紧凑型光子带隙(DUC-PBG)结构的阻带特性,论证了其结构比传统的UC-PBG更加紧凑,因而更有利于实现光子晶体天线的小型化。在提出一种圆极化微带天线的基础上,将这种DUC-PBG结构刻蚀在贴片天线的周围,并使得天线的工作频率落在它的阻带范围内,以此来实现抑制表面波和改善天线性能的目的。通过对该结构进行数值仿真,证实了该设计在抑制表面波、削弱交叉极化分量、提高增益及改善天线的辐射方向性等方面的有效性。     

A reconfigurable slot antenna with switchable polarization

A novel reconfigurable slot antenna architecture allowing polarization switching is presented. The antenna shape consists of a slot-ring with perturbations which are switched on and off using pin-diodes. Two antennas allowing switching either between linear and circular polarization or between two circular polarizations are demonstrated. The antenna architecture is interesting for commercial wireless applications because it is compatible with modern fabrication processes and can be realized on low cost dielectric materials.     

Beam steerable square loop antenna over hybrid high impedance surface

A novel hybrid high impedance surface is presented and a beam steerable four feed square loop antenna is built on this structure. At a test frequency of 4.7 GHz, the proposed hybrid high impedance surface based square loop antenna is 4.69 mm high and has an impedance bandwidth of 650 MHz and directivity of 8.7 dBi. Compared with the earlier reported steerable square loop antenna the new antenna s performance equates to a thickness reduction of 61, bandwidth enhancement of 150 , a directivity improvement of 2 dBi, a co-polar sidelobe reduction of 11 dB, and a cross-polarisation sidelobe reduction of 5 dB.