UWB系统中天线性能对脉冲波形的影响

分析了超宽带无线系统中,天线在发射和接收过程中对基带脉冲信号波形的失真影响.采用了天线系统传递函数描述天线的辐射和接收特性,在暗室中对典型的超宽带印刷天线进行频域特性和时域特性的测量,给出了脉冲信号的辐射和接收过程.研究表明结合天线系统传递函数,可以设计出更符合FCC辐射功率掩蔽的脉冲信号,以及选取出波形保真系数最佳的本地模板信号,从而获得全局性能最优的超宽带系统.     

Power transfer characteristics of a microwave reverberation chamber

Power transfer through a microwave reverberation chamber is studied theoretically and experimentally. Two configurations are employed as follows. In the first, the chamber contains a transmitting antenna and a receiving antenna; in the second, it contains a transmitting antenna and a receiving D-dot sensor. For each configuration a theoretical model is derived and laboratory measurements are carried out for the power gain of the chamber as a function of frequency. The models prove useful in predicting the observed variation of gain with frequency, and they provide insight into the importance of power flow to the chamber walls and to the receiving antenna/sensor     

A closer look at reverberation Chambers - 3-D Simulation and experimental verification

This paper presents three-dimensional (3-D) full-wave simulations of the electromagnetic field inside a medium-sized reverberation chamber. A frequency-domain method-of-moments approach based on the electric field integral equation is used. A synopsis of the computational challenges particular for reverberation chambers is described and a detailed overview on the chamber modeling procedure is given. The electric field inside the chamber is computed and the influence of small geometric details and asymmetries is investigated as well as the effect of different excitations and stirrers. It is demonstrated that a statistics-based validation of reverberation chamber simulations is insufficient. To validate simulation results, therefore extensive near-field measurements inside the prototype reverberation chamber are performed. The complete 3-D reverberation chamber simulation, considering stirrers, door, and various practical excitations, accurately predicts the fields within the chamber in the important lower-to-medium frequency range and thus represents a reliable tool facilitating reverberation chamber optimization.     

Correlation and capacity of MIMO systems and mutual coupling, radiation efficiency, and diversity gain of their antennas: simulations and measurements in a reverberation chamber

MIMO systems are characterized by their maximum available capacity, which is reduced if there is correlation between the signals on different channels. The correlation is primarily caused by mutual coupling between the elements of the antenna arrays on both the receiving and transmitting sides. Similarly, diversity antennas can be characterized by a diversity gain that also is affected by mutual coupling between the antennas. We explain how such MIMO and diversity antennas with mutual coupling can be analyzed by classical embedded element patterns that can be computed by standard computer codes. In the MIMO example under investigation, the mutual coupling reduces both correlation, which increases the capacity, and radiation efficiency, which decreases it, and the combined effect is a net capacity reduction. We also explain how the radiation efficiency, diversity gain, correlation, and channel capacity can be measured in a reverberation chamber. The measurements show good agreement with simulations.     

Transient characterization of a novel ultrawide-band antenna: the scissors antenna

A new ultrawide-band (UWB) antenna named the "scissors antenna" has been designed specially for transient ultrawide-band applications. The scissors antenna, which is composed of conducting wires, radiates ultrashort pulses with very low dispersion. The radiation of this antenna has been characterized by a transient measurement method suitable for characterizing UWB antennas with very low dispersion. After a presentation of the scissors antenna, this measurement method is described. The last part of the paper presents a comparison between the radiation characteristics of the scissors antenna obtained by the transient measurements and those obtained by the classical harmonic measurements.     

Bi-directional UWB MIMO Antenna for Superior Spatial Diversity,and/or Multiplexing MIMO Performance

In this paper, a two-element UWB MIMO antenna with bi-directional radiation pattern is designed for superior UWB MIMO performance. The designed antenna adopts asymmetric coplanar waveguide ground feeding. The proposed antenna ECC is lower than the ECC of its omni-directional peer antenna. Simulated and measured ECC is lower than 0.016 over the entire ultra-wide bandwidth (3.1–10.6 GHz). The isolation between elements of the designed antenna is 20–25 dB exceeding the average in recently published works. The designed antenna has a diversity gain of almost 10 dB and average multiplexing efficiency of 85% over the entire ultra-wide bandwidth. The antenna preserves radiation efficiency higher than 0.96 and gain 3 dB. The diversity performance of the proposed UWB MIMO antenna is proven through real rich-multipath indoor environment measurements. Stationarity of the elected channel is evaluated through 100 successive measurements separated by a 3-min period for 5 h long. The measured spatial correlation coefficients are much lower than 0.5 in different scenarios.     

小型EMC宽带喇叭天线设计

混波室(Reverberation Chamber)作为一种新型的电磁兼容的测量设备,由于其自身的优越性,受到越来越多的关注。应用于混频室内的天线对频带宽度的要求比较高,需要天线能覆盖很宽的频带。提出一种工作频率为2~10 GHz的宽带加脊喇叭天线的设计方法,利用Ansoft HFSS 9软件进行建模仿真,从简化设计以及降低加工难度的角度出发,将喇叭天线的物理尺寸尽可能地减小以方便在空间有限的混波室内使用。将仿真结果与现有喇叭天线实测结果相比较,结果表明,该天线在所设计频带内匹配良好。     

混响室法欠模状态屏蔽体屏蔽效能测试技术研究

欠模状态下屏蔽壳体内部场分布不均匀,屏蔽效能测量结果与位置相关,因此需要利用探头或单极子天线进行多位置测量,过程繁琐。文中利用长线天线来测量欠模状态下屏蔽壳体屏蔽效能,并与单极子天线测量结果进行比较。在暗室中测量天线自由空间反射系数S₁₁;在混响室中利用不同天线测量屏蔽壳体的屏蔽效能,并利用S₂₂分析腔体谐振特性。测量结果表明,长线天线宽频带匹配特性优于单极子天线,测量的屏蔽效能能够更好地反映屏蔽体谐振特性,为屏蔽壳体的屏蔽效能测试评估提供了指南,具有工程应用价值。     

混响室设计与校准测试

给出了混响室测试系统的设计方法和基本性能的预测分析.根据设计建造了混响室,并且采用自动化测试软件完成了校准测试,分析了电场均匀性、品质因数等性能指标.测试表明建造的混响室性能完全符合测试标准的规定,多次测量重复性很好.最低可用频率200 MHz,电场均匀性小于3 dB.可以用来进行电磁兼容辐射发射和辐射抗扰度测试.     

渐变巴伦馈电的超宽带天线单元及阵列研究

为了满足超宽带电子系统对天线的需求, 研究了强互耦超宽带天线单元及阵列.首先设计了能够满足强耦合线极化的天线单元, 然后研究了超宽带相控阵天线阵, 设计了10×10天线单元组成的阵列.以此为基础, 利用高频电磁场仿真软件在二维周期环境中模拟了无限大周期阵列.结果表明, 在满足尺寸约束的前提下实现了二维周期边界下超宽带阵列的功能要求, 同时, 解决了强互耦效应下超宽带无限大偶极子相控阵进行全阵列仿真耗时极多、难度极大的问题.为了解决阵列单元如何有效馈电的问题, 在分析了天线单元结构设计的基础上, 研究了渐变结构巴伦的馈电特性, 并将这种馈电结构与上述强耦合超宽带天线单元相结合, 对单元结构和馈电方式进行了优化, 实现了超宽带馈电的效果.加工了天线阵列并在微波暗室中对不同频点进行了测试, 测试结果与仿真结果吻合.从测试结果可以看出, 主平面辐射方向图在不同频点内的最大扫描角波束峰值增益均大于5 dBi, 最大达到20 dBi, 满足设计要求.说明所设计的阵列天线能够应用于实际微波系统中.     

镜像对称结构对多馈源混响室场性能的影响

为解决混响室大体积与场性能高要求之间的矛盾,提出了一种基于镜像原理的多馈源混响室的设计思想,从原理上分析了镜像多馈源混响室的可行性和有效性,并通过仿真计算研究了镜像双馈源混响室的场性能.结果表明,在输入功率一定时,两个单混响室系统组合成镜像双馈源混响室后,在工作区域的场均匀性能不下降的基础上,不但可用于电磁兼容测试的工作区域体积大幅度增大,而且测试区域的电场强度也得到了提高.同时,对镜像多馈源混响室进行了进一步的扩展分析,得出了组成镜像多馈源混响室的单混响室系统数量的理论表达式.     

双发射天线对混响室场性能影响的数值分析

提出了双天线激励混响室的方法,研究了双天线激励对混响室场性能的影响。分析了双天线改善混响室场均匀性的原理,对单天线激励下的混响室模型以及处于不同位置的双天线激励下的混响室模型进行了仿真计算,从场均匀性和场强两个方面研究了双天线对混响室场性能的影响,对双天线影响场强的机理进行了分析。研究表明:采用双天线激励改善了混响室工作区域的场均匀性;采用双天线可以降低对功率放大器的要求,降低大型混响室测试成本。最后对双发射天线在大型混响室中的应用进行了探讨和展望。     

Performance of a Crossed Exponentially Tapered Slot Antenna for UWB Systems

A compact printed antenna is described that exhibits adequate transient performance for ultrawideband (UWB) applications and it is further adequate for polarization diversity schemes. The antenna is based on an original combination of two crossed exponentially tapered slots plus a star-shaped slot to produce a stable radiation pattern with very stable polarization over the 3.1–10.6 GHz FCC assigned band. Results are confirmed with measurements. Figures of merit like output pulse fidelity and time window containing 90% of the transmitted energy are analyzed over the entire solid angle and showed to remain quite stable, in line with envisaged UWB system requirements. Compact dual-antenna arrangements are also analyzed in view of potential use for UWB multiple-input–multiple-output implementations.      

Investigation of Reverberation Chamber Measurements Through High-Power Goodness-of-Fit Tests

This paper aims to improve the analysis of distribution functions of a rectangular component of the electric field (E_R) and the power received in an overmoded reverberation chamber. All data and analysis were achieved in the Institute of Electronics and Telecommunications of Rennes (IETR) mode-stirred chamber. For the power received on a large antenna, tests are consistent with the exponential probability density function assumption. However, high-power goodness-of-fit tests modify the determination of the lowest frequency from which the ideal underlying theoretical distributions can be associated with measurements. For the electric field in an overmoded regime, a Weibull distribution is proposed to model E_R measurements, instead of the Rayleigh distribution hypothesis, which is rejected by statistical tests. Furthermore, Weibull distribution provides better agreement with standard deviation of samples. An additional experiment with a monopole-like antenna illustrates that the exponential distribution is rejected when the monopole is small with respect to the wavelength, but is accepted when the antenna length is roughly over lambda/4. Experimental results are provided by a large number of goodness-of-fit tests. The paper highlights that the use of adapted critical values is necessary for testing a distribution function whose parameters are estimated.     

超宽带TEM喇叭天线阻抗加载的时域分析

基于时域有限差分法中的阶梯近似方法,分析了超宽带TEM喇叭天线辐射场的时域波形.为了改善宽带TEM喇叭天线拖尾效应,文中利用集总元件的时域有限差分法,详细分析了不同阻抗加载条件下TEM喇叭天线辐射场的时域波形.计算机模拟结果表明,加载吸收电阻可以有效地解决TEM喇叭天线由于低频反射引起的拖尾振荡,改善辐射电场的波形特性.     

The effects of the human body on UWB signal propagation in an indoor environment

Ultra-wideband (UWB) communication systems are investigated for their ability to operate in dense multipath environments. While a great deal of time and effort has been spent characterizing both the indoor and outdoor UWB channels, the effects of human body interaction with a close proximity UWB antenna remains unexplored. Measurements of a commercially available UWB antenna performance in an anechoic chamber and in various indoor multipath environments were conducted. Comparisons of these measurement results indicate that while the human body creates a deep (23.6 dB) in a light multipath environment, this is drastically reduced (6.8 dB) in a dense multipath environment.     

Linear dipole response in a reverberation chamber

A new spatial correlation function is derived for the axial electric field and is compared with the previously known spatial correlation function for the total electric field. The new correlation function is used to determine the average power received by a linear dipole antenna in a reverberation chamber. The result for the average received power agrees with the previous result for an arbitrary impedance-matched antenna derived by the angular spectrum method     

Theoretical investigation of the field conditions in a vibrating reverberation chamber with an unstirred component

In this paper, we examine the use of a vibrating reverberation chamber in which an equipment under test (EUT) is directly illuminated by a source antenna. A three-dimensional theoretical model, based on a simplified ray tracing method has been applied on a reverberation chamber whose dimensions were varied. The field distribution together with the field homogeneity was investigated, introducing the Rice distribution due to the presence of the line-of-sight component between the antenna and the EUT.     

A Theoretical Feasibility Study of a Source Stirring Reverberation Chamber

A novel theoretical feasibility study to reverberate a large metallic chamber is proposed. The method is based on the displacement of a radiating antenna inside the chamber, and the reverberating effect is obtained by coupling the antenna current in different ways with the cavity modes. This technique eliminates mechanical rotating paddles inside the chamber and offers the advantage of a continuous-wave operation compared with the frequency stirring method. The reverberating characteristics of the proposed technique are evaluated by calculating the field statistics. The analyzed situation concerns a real antenna, and its radiation into the reverberation chamber is modeled using Green's function of cavity. The numerical problem is solved by the method of moment. The model has been tested and is able to rigorously characterize the reverberating environment for the design and optimization of antenna configurations to be addressed in future studies.