180元HgCdTe线列器件的冷屏效应与背景限性能

从理论上分析了１８０元ＨｇＣｄＴｅ线列器件的冷屏效应，计算了１８０元ＨｇＣｄＴｅ线列探测器每个光敏元所对应的平面视场角（ＦＯＶ）及其在３００Ｋ背景辐射下的背景限探测率，并将实际的１８０元ＨｇＣｄＴｅ线列探测器件每个光敏元的性能同理论进行了比较，结果表明１８０元长波红外ＨｇＣｄＴｅ线列探测器的性能已经接近室温背景的理论极限．     

线形宽带超声相控阵换能器的声场分析

讨论了一种计算矩形活塞阵元声场脉冲响应函数的简便算法,通过对不同延时量的矩形活塞阵元声场脉冲响应函数进行叠加,得到线形换能器阵列的脉冲响应函数;再施以宽带脉冲激励函数,得到线形换能器阵列的声场分布。比较了3种不同换能器的脉冲响应及声场分布,该法对工业无损检测领域超声成像用换能器参数优化具有重要意义。     

线元天线阵列传输特性实验研究

用脉冲电源产生亚纳秒高斯电脉冲给线元天线馈电,测试线元天线轴线能量的传输特性。实验结果表明,在相同轴线距离处,线元阵列天线轴线能量与单元天线轴线能量之比正比于天线阵列阵元数的平方;阵列天线轴线能量具有慢衰减传输特性;对线元阵列天线不同行、列作适当馈电延迟,可实现辐射电磁波束的空间扫描。所有实验结果在误差范围内与理论计算结果符合。     

一种基于迭代FFT算法的直线稀疏阵列优化方法

介绍了一种基于迭代快速傅里叶变换(FFT)算法的优化方法来实现直线稀疏阵列的峰值旁瓣电平最优化,分析并给出了该方法的详细优化步骤.利用阵列因子与阵元激励之间存在的傅里叶变换关系,对不同的初始随机阵元激励分别作迭代循环,便可以得到最优的阵元分布.在迭代过程中,根据稀疏率将阵元激励按幅度大小置1置0来完成阵列稀疏.通过对仿真结果进行分析,证明了该方法的快速性、有效性和稳健性.     

光纤激光相控阵阵元分布优化方法

提高主瓣的能量集中度和抑制栅瓣问题是当前光纤激光相控阵技术面向应用的关键。文中从说明激光相控阵在技术上难以满足/2的阵元间隔,由此导致诸多栅瓣产生的原因入手,并考虑到目前常用不等间隔栅瓣抑制方法将导致相控阵口径增大的难题,提出了一种将遗传算法引入到光纤激光相控阵阵元分布优化的设想。主要方法是从最大限度抑制栅瓣的角度提出一个与主瓣能量集中度和主瓣/旁瓣对比度相关的适应度函数;将遗传算法中的特征参数与光纤激光相控阵的主要参数相对应;然后以20路阵元/阵元间隔为3倍波长、50路阵元/阵元间隔为20倍波长两种线阵情况为例,分别仿真计算了传统的等间距阵元和不等间距阵元分布,及遗传算法优化阵元分布三种情况,得到的光纤激光相控阵远场能量分布、主瓣能量集中度和主瓣与最大栅瓣对比度,并对其进行了比较。结果表明,遗传算法较等间距、不等间距方法的主瓣能量集中度分别提高了9.69%、3.33%,主瓣与第一栅瓣能量对比度分别提高了13.12%、9%。由此可预期基于遗传算法优化的相控阵有望在同等激光发射总功率下获得更远的作用距离。     

Scanned directivity of linear arrays

Expressions for directivity as a function of spacing, scan angle, and current distribution are presented for uniformly spaced linear arrays subject to the assumption that the element radiation intensity function of each radiator can be expressed in either of the following forms:(1 - sin^{2} theta cos^{2} Phi)^{P}orsin^{2P} theta sin^{2Q} PhiwherePandQare zero or positive integers. By proper choice ofPandQ, these expressions can be used to approximate the element radiation intensity function associated with a linear array of isotropic radiators, parallel short dipoles, collinear short dipoles, and planar equiangular spiral antennas. Analytical results are given for a number of cases, and graphical results are presented for directivity in the direction of scan angle for a linear array of radiators with a uniform current distribution and an element radiation intensity given by the expressionsin^{2} theta sin^{2} Phiin the regiony geq 0and zero in the regiony < 0.     

二维固态有源相控阵失效单元补偿新方法

提出二维固态有源相控阵失效单元补偿的新方法，该方法基于失效单元矩形切割和线性规划方法。可适用于有源阵列多单元任意失效分布的实时补偿。在保证失效补偿后两主平面副瓣性能完全恢复的情况下，用线性规划方法对空间平均融瓣进行了优化。由于采用实数算法，仅需对非失效单元的幅度进行调整。理论分析及模拟计算表明该方法在工程应用中是切实可行的。     

Thinned coincident arrays for the direct measurement of the principal solution in radio astronomy

A new technique is described for the design of a thinned, linear, multiplicative array which directly measures the principal solution of a radio source distribution. The original filled multiplicative array with uniform element spacing /spl lscr/ is first generalized to an array of N/sub 1/+1 subarrays each with M/sub 1/+1 elements. A thinning factor of 1/2 is shown to be possible if M/sub 1/=N/sub 1/. Finally, if each subarray is further divided into smaller subarrays until the smallest are simply two element interferometers, then the principal solution can be directly measured but with far fewer elements. Significant thinning factors are achieved when the array is very large. The method can also be used to measure the principal solution with planar arrays, with very strong thinning occurring for large arrays.     

Multimode phased array element for wide scan angle impedance matching

A method of achieving a matched radiating element in both a phased linear array and a phased two-dimensional array over wide ranges of scan angle has been developed. This method uses two or more propagating modes in each array element such that the reflections of these modes from the array aperture produce a cancellation effect at the element driving terminal. An experimental 32-element linear array was constructed to verify this technique. The measured input VSWR for this experimental array was 1.17 or less over a scan range of ±54 degrees. This result agreed very well with the predicted value. The same method has been shown to be equally effective in achieving matched radiating elements for a two-dimensional array.     

Optimal virtual element patterns for adaptive arrays

A major problem in the use of small arrays is the perturbation in the element patterns due to mutual coupling and diffraction effects. The element patterns differ from each other and need to be corrected in order to obtain an array pattern that is close to the desired one. A matrix method can be used to correct the element patterns by modifying the original input/output weights to corresponding weights for corrected elements and vice versa. In this paper the main goal of the array correction is the maximal identity of the element patterns. In addition to identical element patterns the corrected array is characterized by uniform element spacing, which can be chosen to differ significantly from the element spacing in the real array making the corrected array more like a pure virtual array. For the array correction the linear least square error method has been used. To show the applicability of the virtual array, this method is applied to a typical beam scan case, and also over a frequency band.     

基于DDS和Taylor加权发射波束形成研究

提出了一种对水声换能器基阵的发射波束进行优化控制的方法。首先,根据Taylor加权的计算公式,计算出可获得低旁瓣波束各阵元的幅度加权系数;然后,应用直接数字频率合成(DDS)技术设计出每个阵元偏移一定相位的发射信号;最后,结合高性能现场可编程门阵列(FPGA)技术,设计了8元直线阵的发射波束形成。仿真计算和实验结果表明,文章设计的方法不仅能实现低旁瓣的发射波束,还能很精确地控制发射波束角度,为以后的实际工程实现提供了参考方案。     

Excitation of surface wave on circular-loop array

A method is presented of analyzing surface-wave excitation to an infinite periodic linear array in which only one element is excited and all others are parasitic. The approach taken in the analysis is based on the properties of the periodic structure. A formal solution for the current distribution on the array element is obtained, and the propagation constant of the surface wave is also found. In the case where the array consists of loop antennas, the surface wave can propagate only when the separation of the array element is less than one-half wavelength and the circumference of the loop is less than one wavelength. Calculated values of the propagation constant of an array are in good agreement with the measured results.     

线元天线阵列波束扫描研究

由电磁场理论给出了平面线元天线阵列辐射的瞬态电磁脉冲沿径向坡印亭矢量时间积分的解析解及数值解结果,并利用物理光学理论对所得结果作了对比分析,得到结论:(1)线元天线阵列辐射问题可以简洁地由光栅方程求解;(2)被约束波束的坡印亭矢量时间积分的最大值与阵元数目的平方成正比;(3)保持同一列辐射器元馈电同步,而沿行方向依次作适当馈电时间延迟,可有效将波束控制在预期的很小角域内;(4)保持扫描的半角宽度,线元天线阵列有确定的波束扫描角范围。     

An experiment on antenna arrays with randomly spaced elements

An experimental investigation on the planar array with randomly spaced elements was made by using the holey-plate technique. Two sample arrays, each consisting of 210 elements over a circular aperture of about 56 wavelengths in diameter, were tested at 71.25 GHz. The measured sidelobe levels were -12.8 dB and -13 dB, in excellent agreement with the theory which predicted below -12.8 dB with 90 percent probability and -13.3 dB with 50 percent probability. Further, one may consider the pattern in each plane cutting through the antenna as that of a linear random array. Thus one may study the sample distribution of the sidelobe levels of as many linear random arrays as cuts. The results showed a nearly perfect agreement with the theory, despite the fact that in the theory the mutual coupling effect was neglected altogether. This experiment seems to suggest that when the average element spacing is of the order of a few wavelengths or more, the net coupling effect on the pattern of a random array is generally negligible.     

Linear array of woodpile EBG sectoral horn antennas

A technique is described for creating linear array antennas that conform to the natural stacking sequence of the woodpile electromagnetic bandgap (EBG) material. Each element in the linear array consists of a woodpile EBG sectoral horn antenna. The electromagnetic confinement mechanism within each horn antenna relies wholly on the 3-D EBG of the woodpile material. The array element has a typical sectoral horn pattern with a directional beam in one principal plane and a broader beam in the other. The bandwidth of the sectoral horn is almost equal to that of the defect EBG waveguide. Measured and theoretical results for radiation patterns, impedance bandwidth and gain of a sectoral horn antenna made from alumina are described, and theoretical results for a design made from silicon are presented. It is shown that the layer-by-layer nature of the woodpile EBG material enables sectoral horn antennas to be easily stacked together in the E-plane to create linear arrays. Analysis of the mutual coupling as a function of element separation and its effect on reflection coefficient are presented for a two-element linear array in silicon. Theoretical analyses for fixed and scanned beam linear arrays of silicon woodpile EBG sectoral horns are described and finite-difference time-domain results are compared with array theory. The fixed beam arrays are designed for high directivity while the scanned beam array enables wide angle beam steering through the use of parasitic array elements.     

Self- and mutual impedances of traveling-wave linear antennas

A traveling-wave distribution of current can be produced on a conventional linear antenna, such as a dipole, through resistive loading. The self- and mutual impedances of parallel traveling-wave linear antennas are measured and compared with those of the corresponding conventional linear antennas. The effects of coupling on the input impedance of an array element is discussed, and it is shown that these effects are much less pronounced for traveling-wave antennas, which may be advantageous for some array applications     

Nonlinearities in digital manifold phased arrays

In digital beamforming (DBF), the phase shifter is functionally replaced with a receiver and digital phase rotation. A Taylor series expansion of mixer nonlinearities is used to generate receiver intermodulation spectrums respective of the element position and the iso-Doppler wavefront directions of signal arrival across the array. The dominant intermodulation distortion at each element experiences linear phase errors across the array proportional to the harmonic number and the desired steering direction phase gradient. The array distortion signals are reduced relative to the desired signal by the array factor sidelobe isolation when desired collimation directions exceed a few beamwidths of scan off the array normal vector. The result of the nonlinear down conversion analysis is extended to inphase and quadrature imbalances and batch manufacturing tolerances for element receivers.     

Analysis of injection-locked antenna array including mutual coupling effects

In this paper, the injection locking performance analysis of dipole antenna array with each element loaded with a two-terminal oscillator is presented. The analysis is based on the nonlinear model of oscillator and the linear model of antenna array considering mutual coupling effects. The locking range of injection signal and the array radiated power are obtained by solving an equivalent multiport network. In general, the solutions include stable and unstable solutions. The Routh-Hurwitz stability criterion is then applied to remove the unstable solutions. Numerical results show that the array performance such as frequency locking range and radiated power by taking into account the array mutual coupling effects is quite different from that of an isolated antenna element. In addition, the influence of antenna element spacing upon array locking parameters in this paper is found to be consistent with other existing theories.     

Pattern synthesis of centre fed linear array using Taylor one parameter distribution and restricted search Particle Swarm Optimization

In this article, a new method of pattern synthesis of centre fed, equal distance linear array having single and multiple synthesis objectives has been proposed and statistically investigated. Single objective of reduced side lobe level (SLL) and first null beamwidth (FNBW) has been considered separately. Consequently, multiple objectives of beamwidth and side lobe level have been investigated. Synthesis of linear array for suitable objectives has been investigated on Taylor one parameter distribution with equal progressive phase. Excitation amplitude of each array element is taken as optimization parameter where distribution has been optimized using Particle Swarm Optimization (PSO) for achieving low SLL. Later the same has been incorporated for obtaining suitable FNBW. In our optimization algorithm conventional PSO has been modified with a restricted search PSO (RSPSO) where search space has been predefined within excitation amplitude range. PSO within the defined range searches for optimum excitation amplitude to achieve the desired objectives. In order to illustrate the effectiveness of the proposed RSPSO, simulation results of three significant instances of linear array have been presented for both even and odd number of element. The design results obtained using RSPSO have improved result than those obtained using other state of the art evolutionary algorithms like differential evolution (DE), invasive weeds optimization (IWO) and Conventional particle Swarm optimization (CPSO) in a statistically significant way.     

New approximation technique for current distribution in microstrip array antennas

To reduce the number of unknowns in the moment method solution for microstrip array antennas consisting of complex shaped but identical elements, the current distribution of each element is approximated by the distribution of an isolated single element. The so computed coupling shows excellent agreement with an exact calculation and leads to a tremendous decrease in computation time.<>