An efficient computational method for characterizing the effects of random surface errors on the average power pattern of reflectors

Based on the works of Ruze and Vu, a novel mathematical model has been developed to determine efficiently the average power pattern degradations caused by random surface errors. In this model, both nonuniform root mean square (rms) surface errors and nonuniform illumination functions are employed. In addition, the model incorporates the dependence onF/Din the construction of the solution. The mathematical foundation of the model rests on the assumption that in each prescribed annular region of the antenna, the geometrical rms surface value is known. It is shown that closed-form expressions can then be derived, which result in a very efficient computational method for the average power pattern. Detailed parametric studies are performed with these expressions to determine the effects of different random errors and illumination tapers on parameters such as gain loss and sidelobe levels. The results clearly demonstrate that as sidelobe levels decrease, their dependence on the surface rms/lambdabecomes much stronger and, for a specified tolerance level, a considerably smaller rms/lambdais required to maintain the low sidelobes within the required bounds.     

Crosspolarisation properties of reflector antennas with random surface errors

The crosspolarisation properties of symmetric front-fed paraboloids with random surface errors are investigated. Average crosspolar far-field patterns and crosspolarisation discriminations are computed for different RMS surface errors. The influence of the correlation interval and phase-error model used is indicated.     

Limitations on reflector antenna gain by random surface errors,pointing errors, and the angle-of-arrival jitter

The effects of random surface, pointing, and angle-of-arrival errors on the antenna gain are discussed. It is shown that for manufacturing tolerance ratios greater than 10⁵, the random surface errors decrease the antenna gain only when D/λ>3000. The pointing/angle-of-arrival error causes nonnegligible loss in gain when it exceeds approximately a few tenths of the antenna beamwidth. The gain (and the size) of very large reflector antennas is generally limited by the combined effects of the above errors     

The radiation pattern of a surface loaded ellipsoidal reflector

The radiation patterns of the focus-fed axially symmetric and loaded ellipsoidal antennas inE- andH-planes are calculated by using the generalized method of geometrical theory of diffraction (GTD). The chosen loads are resistive types which are described in terms of surface impedances.     

天线最佳吻合轴向误差的精确计算方法

针对现有的吻合计算,存在以轴向RMS最小为设计目标的吻合,对目前计算轴向误差的方法进行了讨论,指出了某些稍不合理的地方,提出了一个较为准确的计算轴向误差的计算公式,并给出了推导过程.对某两个40米天线和64米天线的有限元模型进行了仿真分析,验证了该公式的合理性.实验结果说明,该方法应用范围更广,在工程中应用此方法可以得到更加精确的误差信,并在此基础上做吻合工作,以便更准确地指导下一步天线的安装和调整,获得更好的天线性能.     

Loss in gain and boresight crosspolarisation in reflector antennas with surface errors

Isolation and loss in gain measurements on reflector antennas with surface errors are revealed. An expression for the probability density of isolation is given in terms of the r.m.s. error. The cumulative distribution function is also discussed. The loss in gain distribution is discussed and related to crosspolar isolation.     

The effect of surface loading on the radiation pattern of aspherical reflector

A complete analysis of the radiation pattern of a center-fed axially symmetric loaded spherical reflector antenna is brought to as successful conclusion. The surface of the above-mentioned antenna is assumed to be loaded by materials whose effect is described in terms of surface impedances. The effect of this loading on the radiation pattern of a perfectly conducting spherical reflector is investigated     

天线表面误差的精确计算方法及电性能分析

提出一种天线表面误差的计算方法,用来精确计算变形表面法向、径向及轴向误差,并推导了相应的计算公式.通过分析某工程7.3m圆抛物面天线在多种工况下的表面误差,及其与ANSYS软件计算结果的比较,证明了该方法的正确性,且计算结果仅为ANSYS软件分析结果的三分之一左右.实验结果说明此方法能够更准确地分析变形天线的表面误差及电性能.在工程中应用此方法分析大型空间天线与地面天线,可明显降低天线设计成本,缩短天线设计周期,并为电气设计人员提供准确的天线变形反射面信息.     

Axial cross polarization in reflector antennas with surface errors of large correlation diameter

Equations for boresight cross polarization and isolation of axisymmetric and offset antennas in the presence of surface errors are derived in terms of numerically computable integrals. Computations revealed that 1) for root mean square (rms) error< lambda/4cross polarization increases monotonically with increasing rms error; and 2) maximum cross polarization occurs when the correlation diameter is 0.5Dfor axisymmetric antennas (0.8Dfor offset antennas). For rms error>lambda/4boresight cross polarization remains almost constant. Furthermore, results revealed that for given correlation diameter and rms error, axisymmetric antennas offer better boresight isolation in comparison with offset antennas having the same polarization efficiency.     

Complete radiation pattern of a focus-fed offset paraboloidal reflector

Complete radiation pattern of a focus-fed offset paraboloid is presented. Forward radiation is computed by physical optics, and wide-angle radiation is calculated by using the geometrical theory of diffraction (GTD). The presented formulation is also capable of calculating the patterns of symmetric paraboloids. Effects of the offset angle and the feed pattern asymmetry on the cross-polar isolation are presented.     

On the radiation pattern of a cornor reflector finite in width

Radiation pattern and gain of a corner reflector antenna finite in width are calculated by means of geometrical method for diffraction. The functionsF(T)sreferred to diffraction by the edges and their images are introduced. In the case of an aperture angle not equal to2pi /m(m: integer) a finite number of images of a dipole are considered, and the waves diffracted by the apex edge are introduced. The cases of aperture angles90deg,45degand115degare computed. The results are compared with the measured results obtained by Cottony and Wilson. In the forward and lateral directions agreements between both results are very good; however, in the rear direction it may be necessary to take into account the effects of the waves diffracted by the upper and lower edges of the reflector, when the length of the corner reflector is not too great.     

Feed position for a parabolic reflector with offset pattern

The best position for a feed for a paraboloid with an offset pattern is determined by deriving the exact form of the phase front in the receiving mode and approximating to a circle. Formulae are derived for obtaining the position of the centre of this circle and the extension to correcting lenses or subreflectors is indicated.     

Radiation pattern of an offset hyperbolic reflector

The radiation pattern of a focus-fed offset hyperbolic reflector is determined by using the uniform geometrical theory of diffraction (UTD) and the uniform asymptotic theory of diffraction (UAT). The patterns predicted by these two theories are observed to differ considerably around incident and reflection boundaries. The effects of the slope diffraction as well as those of additional terms in the improved UTD solution are ignored     

Sensitivity of complex response zeros of linear power inversionarrays in the presence of random amplitude and phase errors

This paper investigates the variation of the complex response zeros, commonly used for source location purposes, of a linear power inversion array with random amplitude and phase errors. In particular, after deriving the zero variances in terms of the optimal weights and the variances of the amplitude and phase errors, a simple guideline relating the zero variances to the number of elements and the amplitude and phase variances is obtained for situations when the sources are well separated and resolvable by the array. Some simulation results are then presented to verify the theoretical derivations     

高平均功率太赫兹自由电子激光装置设计

为满足材料和生物医学等研究需要,中国工程物理研究院(中物院)提出了高平均功率太赫兹自由电子激光(THz FEL)用户装置研制项目。该装置采用准连续波运行的工作模式,太赫兹平均功率约为10 W。通过调节电子束能量和摇摆器的磁场强度,装置输出波长可在100μm(3 THz)~300μm(1 THz)进行调节,以满足不同用户的研究需要。装置主要包括电子源、主加速器、混合型摇摆器、激光谐振腔、太赫兹传输与探测系统等。装置将使用直流高压光阴极注入器作为电子源,主加速器为超导加速器,超导加速器后的电子束能量约8 MeV。该装置将建立成为一个用户装置。     

Computation of random coding exponent functions

Gallager's exponent functionE_{circ}, (rho,p)plays a crucial role in the derivation of bounds for coding error probabilities. An iterative algorithm for computing the maximum ofE_{circ} (rho,p)over the set of input probability distributions is presented. The algorithm is similar to that of Arimoto and Blahut for computing channel capacity. It is shown that the approximation error is at most inversely proportional to the number of iterations. A similar iterative algorithm for computing the source code reliability-rate function also is presented.     

On the design of random pattern testable PLA based on weighted random pattern testing

Programmable Logic Arrays (PLAs) provide a cost effective method to realize combinational logic circuits. PLAs are often not suitable for random pattern testing due to high fao-in of gates. In order to reduce the effective fan-in of gates, previous random pattern testable (RPT) PLA designs focused on partitioning inputs and product lines. In this paper we propose a new random pattern testable design of PLAs which is suitable for built-in selftest. The key idea of the proposed design is to apply weighted random patterns to the PLA under test. The proposed design method was applied to 30 example PLAs. The performance of the RPT PLAs was measured in the size of test set, area overhead, and time overhead, and compared with two other designs in test length and fault coverage. The experimental results show that the proposed design achieve short test length and high fault coverage.     

Computation of the average and harmonic noise power-spectral density in switched-capacitor circuits

Switched-capacitor (SC) circuits are periodically time-varying circuits and the noise at the output of these circuits is cyclostationary. This noise is therefore characterized by the average and harmonic spectral densities. We extend the method proposed in a previous paper to compute the average and harmonic noise-spectral densities in periodically varying circuits. We derive expressions for the average and harmonic spectral densities and use the mixed-frequency-time technique for the computation. The results for the average spectral density are compared with published results. The contribution of the harmonic spectral densities to the average noise-spectral density at the output of a cascaded block is estimated.     

Effects of phase and amplitude quantization errors on hybrid phased-array reflector antennas

The tolerance of hybrid array/refleetor antennas to feed element phase and amplitude quantization errors is examined. The effeets of quantization errors on the peak and root mean square (rms) sidelobes are derived for an example parabolie reflector.     

Effect of error correlations and systematic errors on average arraysidelobes

The effect of error correlations on the average error-induced sidelobe level of a planar array is studied. It is found that correlations among the random errors rapidly decrease the average error-sidelobe level (relative to the level when all errors are uncorrelated) as the correlation radius is increased. However, even though the average error-sidelobe level decreases, there are certain types of correlation that produce large local sidelobe increases. In particular, it is found that a one-dimensional correlation produces a large ridge of sidelobes in the plane orthogonal to the direction of the correlation. Simple results are derived from both the amplitude and the angular width of this ridge