Legendre distribution for radiation pattern

The electromagnetic field from a group of radiators depends upon amplitude and phase distribution of the source. The distributions, which are of considerable interest in the mathematical theory of linear arrays, are the Chebyshev, uniform, triangular, and binomial. The radiation patterns of these distributions are highly directive. The Legendre distribution is considered     

Wire-antenna designs using genetic algorithms

There is a large class of electromagnetic radiators designated as wire antennas. As a rule, an inductive process is used to design these antennas. Either an integral equation is formulated or a simulator is used that gives the current distributions on the wires of the antenna, from which the electromagnetic properties of the antenna can then be determined. Once the antenna properties are known, the parameters are optimized, using guides such as intuition, experience, simplified equations, or empirical studies. However, using an electromagnetics simulator in conjunction with a genetic algorithm (GA), it is possible to design an antenna using a completely deductive approach: the desired electromagnetic properties of the antenna are specified, and the wire configuration that most closely produces these results is then synthesized by the algorithm. In this paper, we describe four antennas designed using GAs. The first is a monopole, loaded with a modified folded dipole that was designed to radiate uniform power over the hemisphere at a frequency of 1.6 GHz. The second antenna consists of seven wires, the locations and lengths of which are determined by the GA alone, that radiates waves with right-hand-circular polarization at elevation angles above 10°, also at 1.6 GHz. The last two antennas are modified Yagis. One is designed for a broad frequency band and very low sidelobes at a center frequency of 235 MHz. The other is designed for high gain at a single frequency of 432 MHz. We have built and tested these antennas     

一种新型红外/毫米波共口径目标模拟器电磁特性的优化设计方法

为了减小反射红外、透射毫米波的介质对红外/毫米波共口径目标模拟器的电场相位分布的影响,提高毫米波信号与红外信号的指向一致性,将几何光学法(GO)和遗传算法(GA)相结合,对红外/毫米波共口径目标模拟器中的反射红外并且透射毫米电磁波的介质表面形状进行优化,且得出了函数表达式.利用电磁仿真软件对优化后的目标模拟器指定距离处电场幅度和相位的分布进行仿真.仿真结果表明:优化后的共口径目标模拟器电磁波相位分布变化很小,毫米波信号与红外信号指向具有良好的一致性.     

基于未知源域重构的无相位近场测量技术

天线的远场对于研究天线辐射特性具有重大意义,由于远场的直接测量有着诸多限制,近场测量技术计算远场因其简洁准确的特点得到广泛应用. 然而,传统的近场测量技术要求获取近场区的幅度和相位分布才能发挥作用,随着天线频率的升高,人们想要在近场区获取准确的相位信息变得十分困难. 为了解决该技术难题,文中提出一种无相位近场测量技术. 利用一个封闭面上的幅度信息重建或猜测出包围待测天线的球面切向电场分布,并采用遗传算法进行全局优化,其最初为四组随机数据,经过数次优化后将逐渐接近准确结果. 仿真结果表明,本文方法能够在忽略相位信号的前提下,计算出准确的远场辐射特性.     

Shape Reconstruction of Three-Dimensional Conducting Curved Plates Using Physical Optics, NURBS Modeling, and Genetic Algorithm

A microwave inverse scattering problem including a method for shape reconstruction of three-dimensional electrically large conducting patches with simple geometries using genetic algorithm is presented. Unknown shape reconstruction algorithm starts from the knowledge of the simulated radar cross-section (RCS) data through back-scattering far-field computation using physical optics approximation. The forward problem involves the computation of the multiple-frequency and multiple-direction RCS of three-dimensional large conducting patches modeled by nonuniform rational B-spline (NURBS) surfaces. The control points of NURBS are the geometrical parameters, which are optimized for the shape reconstruction procedure. The extended stationary phase method and critical cases, which occur in physical optics computations in the forward problem, are also discussed. Noise effect and the influence of increment in the number of control points of a NURBS over the inversion algorithm are investigated as well. Numerical results are presented to verify the operation of the proposed algorithm.     

Characteristics of aperture coupled microstrip antennas withvarious radiating patches and coupling apertures

A full wave moment method is applied to the analysis of aperture coupled microstrip antennas, in which all components of the electric and equivalent magnetic surface currents are considered. The electric current distributions on the rectangular patch for different coupling aperture positions are presented with their radiation patterns. The effects of the coupling aperture shape and size on the input impedance and radiation performance are also discussed. As an example of new radiators, slotted patches are studied, and it is shown that they can be used to achieve dual-frequency operation     

用遗传算法预测印制线路板远场辐射的近场数据采样方法

研究了在近场、远场转换中近场数据的采样技术,包括在何处取样与如何预处理数据.对于一块简单的印制线路板,由遗传算法找到最佳等效基本辐射器.通过矩量法仿真得到线路板不同观测面的近磁场幅度,然后预测了不同频率下的远场模式.     

On One More Property of the Ideal Array Element Pattern

An infinite planar array of controlled elements in the form of overlapped subarrays excited through a multiport circuit is considered. It is analytically shown that the contour element (subarray) pattern with an ideal contour shape corresponding to the absence of backward mutual coupling and, as a consequence, to the 100% element efficiency can be exactly formed at a definite amplitude distribution over the densely arranged small ideal subarray radiators in spite of the fact that each such a radiator in the subarray has low efficiency caused by the presence of backward mutual coupling. If the small ideal radiators are controlled directly (without the multiport circuit), the contour pattern can be formed with 100% array efficiency for any shape of the contour. If the radiators are not ideal, then the efficiency of the array shaping the contour pattern is determined by averaging the mismatch efficiency of the uniformly excited array scanning over the region bounded by the contour pattern.     

Radiation efficiency of dense antenna arrays forming flat-top and contour radiation patterns

Infinite 1D and 2D periodic planar arrays of densely spaced radiators that are used to form flat-top and contour patterns are analyzed. It is proposed to determine the amplitude distributions over the antenna aperture as the Fourier transforms of the window functions corresponding to the respective patterns. The proposed distributions are used to derive the explicit expressions showing that the efficiency of an array with a specified flat-top or contour pattern is equal to the mean efficiency of a uniformly excited array in the scan region covered by the specified pattern.     

Adaptive finite element-boundary integral analysis for electromagnetic fields in 3-D

This paper presents a complete adaptive finite element-boundary integral (FE-BI) analysis scheme for the time-harmonic, electromagnetic analysis of three-dimensional inhomogeneous scatterers/radiators in free-space. The adaptive scheme is based on an FE-BI formulation which yields electric and magnetic field solutions simultaneously. It employs a posteriori error estimates which exploit the availability of both field solutions and estimates error distributions and global solution quality for the electric and magnetic fields separately. It automatically determines which elements should be refined in order to equi-distribute the estimated error, based on the type of refinement requested (h,p or hp). This automatic determination is based on extrapolating the elemental error estimates. The algorithm terminates when specified tolerance levels are reached by the electric and/or magnetic field global solution quality estimates. The only required user specifications within the algorithm are the termination tolerances and the types of refinements to effect. Results are presented which show that within the scope of the presented error measures significant reductions in computational cost may be achieved. The proposed scheme could be used with other types of error estimates and it could be adapted to other FE or FE-BI formulations.     

Phase-Controlled Circular Array Heating Equipment for Deep-Seated Tumors: Preliminary Experiments

This paper presents some preliminary results on the development of a circular phased-array equipment for heating deep-seated tumors. It is shown that radiators having sharp directivity are needed to realize excellent focusing of SAR. Moreover, moment method calculations indicate that linearly polarized helical radiators inversely wound with double wires possess the desired directivity and the near field pattern. Field patterns were measured in phantom (plastic cylinders containing saline water) with a circular array formed by four pairs of azimuthally positioned radiators. Excellent focusing of SAR was observed. The ratio of valley to peak value was 0.74. Steering of SAR maximum by phase control was observed and the distance of movement coincided with that estimated from phase variation.     

新型共口径双频双圆极化微带天线设计

论述了一种共口径双频双圆极化微带天线的设计方法。通过工作于主模和高次模的两辐射贴片嵌套来实现双频双圆极化辐射和满足双馈电端口高隔离度的要求。依据此设计方法按照内外贴片不同频段分配研制了两种天线实物样机,并对天线样机的电性能进行了测量,测量结果表明,天线在两频段上圆极化性能良好,并且双端口隔离度高于35dB,证明了此设计方法的有效性。     

Transient response of the duoconical monopole

Large area radiators such as the duoconical monopole are less frequency sensitive than thin antennas. The dispersive nature of antennas is important especially when they are used to transmit video pulses. This paper presents the numerical results obtained for the duoconical monopole under pulsed excitation. Results include the current distribution on the monopole at different instants of time, the radiated waveforms in different directions, and the waveforms of transmitted and reflected signals on the feeding coaxial line. Numerical results were obtained by applying the inverse Fourier transform to the steady-state time harmonic current distributions and radiation patterns. The above results are then used to find a simple incident voltage waveform that will radiate a "pulse" of "good" shape. The radiated field in different directions are then presented for different parameters of the incident double exponential voltage waveform.     

A genetic algorithm used in a 61-element adaptive optical system

To correct the phase aberrations in a wave-front, a wavefront sensorless adaptive optical (AO) system is set up. A real-number encoding Gaussian mutation genetic algorithm (GA) that is adopted to control a 61-element deformable mirror (DM) is presented. This GA uses the light intensity behind a pinhole on the focal plane as the objective function to optimize, and therefore to omit the procedure of measuring the phase aberrations in the laser wavefront by a wavefront sensor. Phase aberrations generated by the DM are brought to an ideal incident wavefront. Several correction simulations have been accomplished. The simulation results show that the genetic algorithm is capable of finding the optimum DM shape to correct the phase aberrations. After the phase aberrations of the wavefront have been corrected by GA, the peak light intensity on the focal plane can be improved at most by a factor of 30, and the encircled energy Strehl ratio can be increased ultimately to 0.96 from 0.032. It is also found that the convergence and stability of the 61 voltages on the DM is quite well. The simulation results prove that the genetic algorithm can be used in AO systems effectively.     

Slot stripline circular-polarization antennas for a few-element antenna array for a high-accuracy receiver of signals from global navigation satellite systems

New radiators for slot stripline leaky-wave circular-polarization antennas for high-accuracy GLONASS/GPS receivers have been developed. The main technical characteristics of antennas with new radiators have been theoretically and experimentally studied. It is shown that application of the new radiators improves the axial ratio, increases suppression of the cross polarization, increases the stability of the antenna phase center, and thus can increase the GLONASS/GPS positioning accuracy. The results of the analysis of the GLONASS/GPS positioning accuracy with the use of these antennas in an angle-measuring receiver and as elements of a few-element antenna array are presented.     

基于多个分数阶次的复杂光场相位恢复算法

给出了一种基于多个分数阶次的复杂光场相位恢复迭代算法。首先利用输入面和两个较高分数阶输出面上的强度信息,恢复出输入面相位分布的轮廓,然后再利用输入面和两个较低分数阶输出面,进一步恢复出相位分布的细节。分别针对具有缓变相位、随机相位分布的光场,进行了二维相位分布的恢复,都得到了良好的恢复结果。最后在一维情形下分析了探测噪声和光路位置调整误差对算法稳定性的影响。     

A partitioned polynomial integration algorithm for failure probability evaluation

Devices and components are subjected to stresses of certain types which the device must withstand to maintain proper operation. The applied stress and the withstand capability of a device are typically random quantities with associated probability distributions which can have arbitrary shapes. Previous workers approximated these distributions by standard shapes, for example, normal or Weibull, to calculate the failure probability analytically. This letter avoids the approximation of distributions and presents an efficient algorithm which can handle any distribution shape with complete control of the computation accuracy.     

Spherical array self-mixing oscillator antenna

A spherical array self-mixing oscillator antenna is designed by applying the injection locking technique to the spherical array of Gunn diode mounted waveguide radiators. The beam steering with considerably constant pattern and low cross-polarisation can be accomplished without using the sophisticated phase shifters. This antenna is designed and tested at the frequency of 10 GHz     

Electromagnetic inverse scattering of multiple two-dimensional perfectly conducting objects by the differential evolution strategy

Electromagnetic inverse scattering of multiple two-dimensional (2-D) perfectly conducting objects with transverse magnetic (TM) wave incidence by the differential evolution strategy (DES) is presented. The governing electric field integral equations for the scattering problem are expressed as surface integral over the cylinder contours. The cylinder contours are approximately represented by closed cubic B-splines local shape functions in local polar coordinate system. The inverse problem is to locate the cylinders and to reconstruct their shape with or without a priori knowledge of the number of cylinders. It is cast into an optimization problem and is solved using the DES. Both synthetic and real reconstructions are carried out. The reconstruction results agree with the true profiles very well. Comparison with the real-coded genetic algorithm has been carried out. It has been observed that the DES outperforms the real-coded genetic algorithm.