Radiation pattern synthesis for circular aperture horn antennas

A set of radiation pattern functions, suitable for synthesis of radiation patterns from circular aperture horn antennas, is obtained by assuming an aperture distribution consisting of the fields of cylindrical waveguide modes. A technique is presented for using a linear combination of the radiation pattern functions to approximate a desired radiation pattern. Linear combinations of the radiation pattern functions resulting in maximum secondary gain, when used to illuminate a paraboloidal antenna, are obtained empirically. Using spherical wave theory, maximum performance theoretically obtainable from an antenna is derived as a function of the aperture size of the feed system; the feed efficiency resulting from these theoretical limits on performance is compared to the feed efficiency of patterns obtainable from circular aperture horn antennas, and to experimental results of attempts to realize optimum circular aperture horn patterns.     

Mutual coupling between circular waveguide-fed apertures in a rectangular ground plane

A method is presented whereby the infinite ground plane analytical model for the self- and mutual admittances of waveguide-fed apertures can be supplemented (using the geometrical theory of diffraction) to include the edge effects of a rectangular ground plane. TheH-plane coupling between twoTE_{11}mode excited circular apertures is calculated and compared with measurements.     

Radiation pattern of a stripline excited rectangular aperture

Numerical results of the aperture field and the radiation pattern of a stripline excited rectangular aperture antenna are obtained by the moment method.     

Optimal scale factors for Gaussian field expansions for a circular aperture

Gaussian field expansions for circular aperture antennas are reviewed, and a method for finding optimal scales in these expansions is given, paralleling the method for rectangular antennas presented in an earlier paper. This procedure is shown to lead to approximations structured in the sense that the number of lobes in the approximation corresponds to the number of terms retained in the expansion. An example is given of the development of a cosine distribution from the aperture, through the Fresnel region, to the far field.     

Analysis and element pattern design of periodic arrays of circular apertures on conducting cylinders

The analysis and the design of elements for a large array of circular apertures on a triangular grid is approached by modeling the antenna as an infinite structure rotationally symmetric and periodic along the cylinder axis. Because of this particular symmetry, every possible excitation is the superposition, with suitable weights, of a set of fundamental excitations having uniform magnitude and linear phase progression in the azimuthal direction and in the direction of the cylinder axis ("eigenexcitations"). Thus by invoking superposition, the electromagnetic analysis of the array is reduced to the solutions of the simpler boundary value problems pertinent to the set of eigenexcitations. This is done by expanding the field in normal modes in the region exterior to the cylinder and in the waveguides feeding the apertures, followed by a field matching at the cylinder surface (obtained approximately through Galerkin's method). The realized gain pattern of the radiators can be modified to a considerable extent by using an "element pattern shaping network" (in the radiator waveguides), serving the purpose of matching the array for a selected eigenexcitation. Criteria for the network design are given. A series of numerical examples illustrate the technique and shows that a "flat" element pattern can be thus obtained with a gain falloff with respect to the peak of less than 6 dB at 80 degrees, and an increase of 2 to 3 dB in the gain at 80 degrees with respect to that obtained for the same elements matched at broadside.     

矩形栅格圆口径平面相控阵天线方向图计算

针对机载相控阵雷达天线受机头圆柱形设备舱约束的条件,研究了矩形栅格圆口径平面相控阵天线的方向图,建立数学模型并对其进行了公式推导和计算机仿真。同时将该天线与同等规模的矩形口径平面阵天线方向图特性进行了对比分析,结果表明:前者通过展宽主波束宽度和抬高旁瓣间交叉电平深度获得了优于后者的抗干扰性能的结论。     

The transmission coefficient of elliptical and rectangular apertures for electromagnetic waves

A simple scalar method using Kirchhoff's boundary values is applied to the diffraction problems of circular, elliptical, and rectangular apertures for normally incident electromagnetic waves. As far as circular apertures are concerned, a simple formula can be derived not only for the diffraction pattern but also for the transmission coefficient. This formula yields good results for apertures greater than0.8lambda. Even in the ease of elliptical apertures a simple formula can he derived for the diffraction pattern. For the elliptical aperture, as well as the rectangular one, the transmission coefficient was found in the form of an integral. Relief models and diagrams are given for the transmission coefficients of the elliptical and the rectangular apertures as a function of the two aperture parameters. Diagrams are given which explain the dependence of the transmission coefficient on the aperture parameters. A comparison with other more complicated methods of approximation and with measurements shows both good agreement and the great practical value of the simple method of approximation used.     

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.     

非对称方孔的夫琅和费和菲涅耳衍射

基于标量衍射理论,对均匀平面波通过两个非对称双矩孔的衍射作了解析研究和数值计算,给出了夫琅和费和菲涅耳衍射的横向、轴上和轴外光强分布。研究表明,可用其最大光强的相对误差来区别夫琅和费和菲涅耳衍射,所得结果与两个圆孔情况一致。     

有孔矩形腔的屏蔽效能及其对谐振抑制研究

介绍了用传输线解析计算法分析有孔矩形腔屏蔽效能的基本原理,对基本公式作进一步修正,使其能计算孔阵列情形,并对修正的传输线模型计算公式进行了扩展,使其能计算任意极化方向时的情况.通过在腔体内表面敷设经过优化计算的复合电介质涂层,实现了对特定谐振频率抑制.计算和仿真结果表明:当处于谐振频率时,屏蔽系数很低甚至为负;孔阵的屏蔽效能比相同面积的单孔的屏蔽效能好;屏蔽效能随极化角度增加而变化,当耦合电场极化方向平行孔缝的长边时,屏蔽效果最好;在腔体内表面上敷设对应腔体谐振频率的复合电介质涂层,实现了在相同的厚度条件下对腔体谐振频率最佳的抑制效果.根据计算结果提出了设计屏蔽腔的建议.     

New plane wave spectrum formulations for the near-fields of circular and strip apertures

The plane wave spectrum (PWS) method has previously been applied to analyze the near-field of planar apertures. The main goal of this paper is to present new PWS formulations for the near-fields of strip and circular apertures. Only special cases are developed in detail. For example, the uniform and parabolic aperture distributions are developed for the circular aperture. These new formulations are expressed in terms of either elementary functions or Fresnel integrals. Consequently, they permit considerably more rapid and efficient calculations than previous near-field formulations, by either the PWS or the aperture integration approach. The new formulations are especially advantageous for large circularly symmetric apertures (on the order of100lambdaand larger) in that computational efficiencies are improved by an order of magnitude or two over the original PWS formulation. The improvement over aperture integration techniques is more than a factor of 1000 for the100lambdaaperture.     

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.     

A circuital approach to evaluating the electromagnetic field on rectangular apertures backed by rectangular cavities

In this paper, the problem of evaluating the electromagnetic field on rectangular apertures backed by rectangular cavities is investigated. The electromagnetic-field distribution is derived by using a circuital model of an aperture and suitable forcing terms introduced into the equations related to the aperture model. The effects of a rectangular cavity on the aperture-field distribution are assessed by considering the rectangular cavity as a load impedance. The impedance value is obtained by modeling the rectangular cavity as a length of rectangular waveguide back-ended by a short. The distribution of the electromagnetic field on the aperture is used as an exciting source to evaluate, through a modal expansion, the electromagnetic field inside the cavity. Numerical simulations are in a good agreement with both other theoretical models and experimental data.     

Shaped beams from circular apertures and arrays with uniformamplitude

It is shown that shaped beam patterns with acceptable ripple and sidelobe levels can be obtained from circular apertures or arrays with uniform excitation amplitude     

A design procedure for classical offset dual reflector antennaswith circular apertures

A geometrical optics procedure for designing electrically optimized classical offset dual reflector antennas with circular apertures is presented. Equations are derived that allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The procedure, together with these equations, yields an optimized design, starting from general system requirements. The procedure is demonstrated by designing both an offset Cassegrain and an offset Gregorian antenna, and is validated by analyzing their radiation patterns using physical optics surface current integration on both the main and subreflectors     

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     

贝塞尔-高斯光束通过圆孔与圆环光阑的衍射

为了研究贝塞尔-高斯光束通过圆孔硬边光阑和圆环光阑的衍射特性,从Collins公式出发,采用数值模拟的方法模拟出光强分布.模拟结果表明,贝塞尔-高斯光束经圆孔光阑衍射后轴上光强随菲涅耳数F呈周期振荡;贝塞尔-高斯光束经圆环光阑后轴上光强随F呈振动衰减.在F相同时,贝塞尔-高斯光束经圆孔光阑衍射后横向光强分布比经圆环光阑衍射后横向光强分布平滑,孔径越小,光强调制越明显;当孔径与束腰相等时候,横向光强分布与菲涅耳数没有关系.     

基于有限元法的孔缝结构矩形腔屏蔽效能数值仿真

微弱信号检测设备因其检测对象的幅值比较小且易受电磁噪声干扰,所以如何有效地抑制外部电磁干扰非常重要。以微弱信号检测电路的屏蔽腔体为研究对象,采用有限元法对具有孔缝结构的矩形腔体进行建模仿真,分析孔缝的尺寸、形状对屏蔽效能的影响。仿真结果表明：采用多排圆形小孔代替相同面积的矩形缝隙在0.1GHz~0.8GHz范围内屏蔽效能提高了20dB以上,在0.8GHz~1GHz范围内提高了35dB。同时得到屏蔽腔体的谐振频率以及腔体内部不同位置处的屏蔽效能。仿真结果有利于电路和器件的合理布局,进而提高微弱信号检测设备的抗电磁干扰能力。