A note on the directivity of a uniformly excited circular aperture in an infinite ground plane

The directivity of a uniformly excited circular aperture in an infinite ground plane is reexamined in the light of recently acquired knowledge related to Q-type integrals. It is seen that depending on aperture size, numerical corrections to the directivity estimates for such apertures can be easily accommodated.     

一种阵列天线的约束最优化综合方法

为同时满足对方向性系数,阵列效率,方向图旁瓣等参数的要求,提出了一种效率和旁瓣约束下的最优方向性综合法.该方法适用于任意的阵列形式,以最大化阵列方向性系数为目标,通过对加权向量的二次约束控制了阵列效率,并采用迭代的方法满足了方向图旁瓣的要求,实现了阵列效率和旁瓣约束下的方向性系数最优化.对多种阵列在不同要求下的仿真结果以及5元圆阵列的实验结果表明了这种方法的有效性和灵活性.     

圆口径正馈抛物面天线的近场分析

分析了圆口径正馈抛物面天线的近场.采用口径场绕射积分求取了天线的近场及远场方向图,绘制了波束宽度、方向性和最大副瓣电平三个关键参数随场点距离的关系曲线.通过与物理光学法的计算结果对比,验证了该方法的正确性.仿真结果是:随场点距离的减小,波束宽度展宽,方向性减小,最大副瓣电平在一定范围内波动.场点在D2/λ外,远场近似的波束宽度误差小于1%;在0.5D2/λ外,远场近似的波束宽度误差小于10%;在0.5D2/λ内,不能采用远场近似.     

Aperture Coupling Between Dielectric Image Lines

Aperture coupling between dielectric image lines is used develop a design technique for directional couplers at millimeter-wave frequencies. Expressions for coupling coefficients and directivity, employing coupling between image lines through apertures in the common ground plane are developed. The design procedure is illustrated by application 10-, 20-, and 30-dB directional couplers in rectangular image lines with circular aperture coupling.     

A radiometric antenna gain calibration method

A radiometric method is presented for measuring the power gain of a microwave antenna. It is particularly applicable to horns with gains in the range 20-45 dB, and an absolute uncertainty (3sigma) of less than 0.1 dB is achievable in favorable cases. An absorbing screen with a circular aperture is placed in the far-field of the test antenna. The diameter of the aperture is chosen to subtend an angle much smaller than the main lobe of the radiation pattern of the test antenna. Then two sheets of microwave absorber (one at ambient temperature and the other cooled to the boiling point of liquid nitrogen) are alternately placed first behind the screen aperture and then, for normalization, across the aperture of the test horn. The ratio of the antenna temperature differences measured with a sensitive microwave radiometer is proportional to the effective antenna solid angle, and thus its directivity. Corrections must be applied for near-field effects, diffraction at the screen aperture, partial resolution of the screen aperture by the main lobe of the test antenna pattern, and ohmic losses. A comparison of black disk measurements using a large conical horn at 86 GHz with theoretical calculations confirms the accuracy of this gain calibration technique.     

Gain-area product of circular aperture

Tables of the gain-area product of a circular aperture are given and explained. Particular attention is given to the realization of maximum gain over a given area with no constraints on aperture size, but with a simple in-phase aperture distribution; and with a given aperture size, using the same class of illumination function     

一种改善圆阵波束指向性性能的加权方法

该文在分析圆阵波束指向性的基础上,提出了一种改善圆阵波束指向性性能的对称指数加权方法,利用该方法能较有效地抑制旁瓣,而主瓣的增宽效应并不明显。     

Wide-band circular groove guide horn antenna

A novel horn antenna based on a circular groove guide is analyzed and measured at Ku-band and Ka-band, respectively. This horn antenna can cover a frequency range from 14 to 40 GHz. Its optimum dimension was obtained according to the maximum directivity. The antenna can be matched efficiently to free space through its large aperture. Moreover, its input VSWR is low. The theoretical radiation patterns are close to the measured ones.     

Optimum aperture monopulse excitations

A unified formulation of the optimization of monopulse antenna performance indices for a specified sidelobe envelope function and/or specified nulls of the pattern is presented. The performance indices considered are beam efficiency, gain factor, and angular sensitivity factor of rectangular and circular apertures. The unconstrained optimization of beam efficiency result in an integral equation, the solutions of which are prolate spheroidal wave functions for rectangular aperture and hyperspheroidal wave functions for circular aperture. These functions reduce, respectively, to Legendre and Zernike polynomials in the case of gain factor and angular sensitivity factor. The double orthogonality properties of these eigenfunctions are used for constrained optimization. The results obtained by this technique for the near-in sidelobes constrained at a uniform level are shown to be in agreement with the earlier works. The method is applicable for other aperture surfaces such as elliptical, ellipsoidal, and spherical.     

Radiation from a homogeneous sphere mounted on a waveguide aperture

The results of an experimental and theoretical study of the effects of placing a dielectric sphere over the aperture of a circular waveguide are presented. A dielectric sphere excited by a Huygens' source is used us the theoretical model to interpret the experimental results. Calculations based on this model show good overall agreement with experimental patterns and directivity measurements. It is concluded that dielectric loaded antennas such as the dielectric sphere excited by a waveguide can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of two wavelengths or less. Measurements of the coupling between these antennas show that they, in general, are not as closely coupled as plain apertures without dielectric object loading.     

On the aperture and pattern space factors for rectangular and circular apertures

A consequence of a recently discovered edge condition for planar apertures is that all planar aperture distributions are separable physically into a product of an edge factor and an aperture space factor, analogous to the way in which the radiation pattern separates into a product of an element factor and a pattern space factor. An exact relationship between these aperture and pattern space factors for physically realizable vector fields is derived here for rectangular and for circular apertures. For rectangular apertures it leads to a two-dimensional set of doubly orthogonal functions that are characteristic of the aperture geometry. Characteristic functions for circular apertures, however, are shown to exist only if the vector fields are circularly symmetric, although for scalar fields they exist for completely arbitrary aperture distributions with arbitrary edge taper. For rectangular apertures the characteristic functions consist of products of spheroidal functions and for circular apertures they are obtained from a generalization of the spheroidal functions. Some of the properties of these generalized spheroidal functions are developed here.     

一种低旁瓣非均匀圆形活塞换能器的设计

针对水声换能器的指向性旁瓣级问题,该文提出了一种低旁瓣非均匀圆形活塞平面水声换能器。该换能器在均匀圆形活塞换能器的基础上,采取去双环分布方法去除均匀圆形活塞换能器部分压电相体积,改变换能器结构,实现了抑制旁瓣的效果。以均匀连续平面活塞阵为基础,该文推导了去双环圆形平面活塞阵指向性函数,并采用Matlab对该指向性函数求解,分析两个环的位置和宽度随换能器指向性最大旁瓣级的变化规律,根据优化结果确定了换能器的最优尺寸。通过有限元仿真分析表明,该去双环圆形活塞换能器指向性最大旁瓣级为-25.3 dB,与均匀圆形活塞换能器相比,最大旁瓣级降低了8.3 dB,实现了旁瓣抑制,有效降低了最大旁瓣级。     

多约束天线阵列遗传优化中的初始群体构造方法

针对运用遗传算法进行圆形口径的平面稀布天线阵列的优化设计,提出了一种有效的初始群体构造方法,它能满足多个实际工程设计的约束条件.由此方法构造的初始可行解可作为遗传算法的个体,从而组建初始群体,它为多约束遗传优化算法的运用提供了可行性.该方法的正确性和有效性也得以认证.     

Synthesis of the antenna pattern for a radiating slot in a metal cylinder

The synthesis of a prescribed far-field pattern by means of a radiating slot in a perfectly conducting infinite circular cylinder is considered. The narrow circumferential slot and the infinite axial slot are studied in detail. In either case, the problem is to find the distribution of the electromagnetic field in the aperture that yields a radiation pattern that is the best mean-square approximation to a given pattern, under certain constraints. Various quality factors for cylindrical modes are discussed, and a detailed comparison with the synthesis problem for a planar aperture is performed. It turns out that Rhodes' synthesis method has no equivalent in the cylindrical case, and that the best admissible mean-square approximation to a given pattern may be a very poor approximation in amplitude. However, an iteration scheme is developed in which the phase approximation is sacrificed for the sake of substantially improving the amplitude approximation. Numerical results based on such a scheme are displayed, for prescribed omnidirectional and sectoral patterns.     

Optimum distribution over a circular aperture for best mean-square approximation to a given radiation pattern

The distribution over a cicular aperture in a ground plane that produces the best mean-square approximation to a specified radiation pattern is derived subject to constraints on the mean-square aperture field strength. The result is derived in terms of the functions most natural for a least square fit: the eigenfunctions of a finite (circular) two-dimensional Fourier transform.     

一种超方向性阵列天线综合方法

以往的阵列综合方法不能在获得高的方向性系数的同时保证外部噪声占优,不能用于超方向性阵列综合 .本文提出了一种新的阵列综合方法,该方法适用于任意阵列形式,以最大化阵列方向性系数为目标,通过对阵列效率的约束保证了外部噪声占优的条件,并通过迭代控制了方向图的旁瓣,实现了阵列效率和旁瓣约束下的方向性系数最优化,很好地满足了超方向性阵列综合的要求 .对多种阵列的综合结果表明了这种方法的有效性和灵活性 .     

基于孔径长度域重采样的快速恒定束宽波束形成

为解决宽带阵列天线波束宽度抖动的问题,在分析阵元权系数和阵列方向图傅里叶变换关系的基础上,提出了一种基于孔径长度域重采样的快速恒定束宽宽带波束形成方法。该方法通过期望方向图的傅里叶反变换获取孔径长度域上的权系数曲线,然后用不同的采样间隔对该权系数曲线进行重采样得到不同频率下的阵元权系数。由于仅需进行一次积分运算,该方法具有运算量小、速度快的特点。为使阵列方向图在恒定束宽的基础上具有更好的方向性,通过对孔径长度域拟合度的分析给出了期望方向图的设计方法。仿真结果表明所提方法可以快速形成方向性较好的宽带阵列恒定束宽方向图。     

收发等波束的双频低副瓣多波束天线

介绍了一种可实现收发波束大小一致的工作于K/Ka频段的低副瓣反射面多波束天线系统。该天线系统采用高效率双频多模喇叭作为馈源,实现了收发频段共用同一反射面,极大地降低了系统的规模。通过对反射面口径场上幅度和相位的分布对天线二次辐射方向图的影响的分析,提出了一种在高频处对反射面引入副瓣照射的方法,从而实现了收发波束大小一致。该天线系统在收发频段均体现了良好的低副瓣、高载干比特性。     

圆弧阵中加权子空间拟合算法对目标的估计性能分析

本文以声纳系统中常见的圆弧阵为例，通过将其投影到一条直线上而等效为一线列阵，分析了高分辨的加权子空间拟合算法在圆弧阵中对目标方位的估计性能。计算机仿真结果表明，是否考虑单个技能器的指向性，对算法性能的影响不大。当换能器基阵有一定的声学孔径之后；增加阵元的个数不会明显地改善算法的估计性能，而运算量却大幅度地增长。     

Theory and measurement of the field of a pyramidal horn

Edge-wave diffraction theory is used in an unconventional way to predict the field in the immediate vicinity of the aperture plane of a pyramidal microwave horn. The far field may then be inferred by Fourier transformation. The theoretical predictions for the near field are compared with measurements almost in the aperture plane and inside a horn made by the modulated scatterer method. The directivity on axis, which is our primary concern, is mainly determined by the curvature of the wavefront at the aperture. When computed as a function of frequency, it shows oscillations similar to those observed. They arise because edge waves, multiply reflected inside the horn, mimic the effect of a wave reflected back from the throat; this interferes with the main wave to change the curvature of the emerging wavefront, and hence, the directivity