A uniform asymptotic evaluation of integrals

Previous uniform asymptotic evaluations of integrals have been restricted to cases where the integrand singularities are close to the saddle point(s). A method is presented here which allows such uniform evaluations with integrand singularities anywhere near the steepest descent path.     

A spatiotemporal representation of the electromagnetic field radiated by short-pulse superwideband antennas

It is shown that two approaches can efficiently be applied to calculate impulse responses of antennas radiating superwideband signals. The simultaneous use of these approaches makes it possible to lucidly describe the operation of certain antennas and substantially simplify the calculations. The impulse responses of some short-video-pulse scanning array antennas and the shapes of radiated signals are calculated.     

Analysis of rectangular horn antennas via uniform asymptotic theory

Approximate analytic expressions for the far-field radiation pattern and modal reflection coefficient of the three-dimensional horn antenna have been developed. Based upon a multiple-image model of the two-dimensional horn-waveguide structure, this approach offers greater generality than previously proposed ray analyses with comparable complexity and accuracy. The uniform asymptotic theory (UAT), which is employed throughout, provides information when this approach is valid for a desired degree of accuracy in the solution. It is demonstrated that, in most cases, the far-field pattern of the horn is reducible to the pattern of a simple slit in an absorbing screen illuminated by an array of patterned line sources. The measured patterns of several horns are convincingly recovered by the prediction of the analytical model. The same model is used to calculate the modal reflection coefficient of the horn-waveguide structure and, again, comparison with measured results is excellent.     

机载相控阵天线绕射场分析

采用一致性几何绕射理论分析了某型航空飞行器机体对其上安装的阵列天线辐射方向图的影响.给出了机体散射场分析数学模型建立的原则和天线装机后总场计算方法,详细推导了阴影区曲面绕射场的计算公式,分析了载机对天线辐射方向图的影响.以相控阵天线为例,计算在机体上不同安装位置,天线不同扫描角情况下的天线辐射方向图,为大型阵列天线在载机上的优化布局提供参考.     

A slot design for uniform aperture field distribution insingle-layered radial line slot antennas

A single-layered radial line slot antenna (RLSA) is proposed for a direct broadcast from a satellite (DBS) subscriber antenna. It utilizes a radially outward-traveling wave and the aperture field is intolerably tapered if the uniform slots are used. Two novel techniques are applied. First, the slot design for uniform aperture field distribution is introduced. Second, the radial line is terminated by a matching spiral, in place of a dummy load. It suppresses reflection and radiates all the residual power in circular polarization. For a model antenna of 600-mm diameter, the efficiency of 65% is observed     

A NEW METHOD FOR COMPUTING RADIATED FIELD OF REFLECTOR ANTENNAS——THE CHEBYSHEV-BESSEL SERIES TECHNIQUE

A rapidly convergent series—the Chebyshev—Bessel series for representation of the physical optics (PO) radiation integral is developed, which is applicable to evaluating radiated field of reflector antennas.     

Statistical characteristics of the field of an array of random aperture antennas

The subject area and the initial data for statistical simulation of the field generated by an antenna array consisting of three rectangular apertures excited by a random signal and representing a three-element aperture random antenna (RA) are considered. Results of the analysis of statistical characteristics of the amplitude and phase of the RA field are presented in the form of histograms of their random deviations from deterministic values, which are caused by the influence of amplitude and phase errors.     

Numerical analysis of collinear monopole antennas with coils

Double-band operation (85 and 900 MHz) of a collinear monopole antenna is numerically demonstrated. The antenna consists of three linear wires connected with two coils, and has a height of 67 cm. One coil acts as a phase compensation element to increase the gain and the other as a decoupling element for use in the mobile telephone band.<>     

Pattern synthesis of array antennas with additional isolation ofnear field arbitrary objects

A new technique for synthesising array antennas in the presence of arbitrary obstacles in the near field region is presented. This technique allows a prescribed far field pattern to be synthesised, while trying to avoid coupling with near field obstacles through the constraint of minimising the radiated power over the obstacle surface. Some results have been obtained showing that the obstacles are finally isolated from the array antenna radiation     

A modular approach for the design of microstrip array antennas

A method for the design of medium gain (15-25 dB) microstrip array antennas is described. A modular approach is utilized in which a given antenna is used as a building block for higher gain antennas. A series ofX-band antennas were built in this way, and the results seem to validate the usefulness of the method.     

A study of microstrip array antennas with the feed network

The radiation and losses in microstrip antennas with a corporate feed network are studied. A surface current approach is applied in which the electrical currents in the feed lines are modeled as in ideal transmission lines. The free-space radiation and the surface-wave excitation of typical segments in printed feed networks are studied. A four-element array antenna with its printed feed network is analyzed and predicted radiation patterns, directivity, and gain are presented and compared with experimental results. The gain and directivity of large arrays of 16, 64, 256 and 1024 elements are calculated and measurements in the frequency range of 10 to 35 GHz are reported     

Analysis of printed array antennas

A simple but efficient analysis tool for printed antenna arrays is presented. It relies on a perturbation approach, which starts from the infinite periodic array assumption to ultimately take into account effects due to finite size, nonperiodicity, double-periodicity in a multilayer case, complex excitation with nonlinear phase shifts between elements, etc. The technique is an approximation, as are most of the array analysis tools. However, it gives good results for arrays presenting a relatively smooth variation of the antenna characteristics between adjacent cells. Results will be shown for several arrays, including nonperiodic and multilayered cases. The method is validated through the comparison with results obtained by a rigorous element-by-element method     

A new technique for planar array antennas synthesis

A novel technique, conceived and baptized the immunity tactic will be presented in this paper. As one will see, we classify the technique under the stochastic processes while governed by deterministic rules. This technique was greatly inspired by the immune activity, which has the tendency to eliminate the strange bodies and to preserve the self-organism. The analogy with the synthesis will be as follows:

• Elimination of all the weak solutions.

• Preservation of the best solution.

Some biologic immunity operators will be borrowed and adapted to our technique, which remain governed by deterministic rules to avoid any destabilization.     

Fundamental properties and optimization of broadside radiation from uniform leaky-wave antennas

In this paper, radiation at broadside is studied for a general class of leaky-wave antennas (LWAs) comprised of a grounded slab covered with a partially reflecting surface, on the basis of a simple transverse equivalent network model of the structure. The analysis of the one-dimensional (1-D) version of such a LWA excited by a line source shows that a central role in establishing the features of broadside radiation is played by the condition that the phase and attenuation constants of the leaky mode responsible for radiation are equal. When this happens, a beam with a single peak at broadside is on the verge of splitting into two distinct peaks, and maximum power density is radiated at broadside. Design formulas to achieve such an optimized condition, as well as approximate expressions for the frequency bandwidth and pattern beamwidth of the antenna and for the leaky-wave phase and attenuation constants are derived, both in the absence and in the presence of losses; in addition, an optimal-beamwidth condition (which gives the narrowest broadside beam) is derived. Finally, all the results are extended to the practical case of a 2-D LWA excited by a horizontal dipole.     

A generalized approach to the analysis of infinite planar array antennas

In this paper a generalized expression for the complex power radiated by an element in an infinite planar array antenna is derived. Since this power formula applies to a large class of phased array antennas where the aperture field distribution can be completely specified (in normal mode form), it proves to be a powerful, unifying principle. The utility of this approach is illustrated by the simplicity with which previously known results can be derived; e.g., an infinite array of slots in a ground plane and an infinite array of flat dipoles with or without a ground plane. Further demonstrations of the usefulness of the power formula are provided by the systematic and straightforward solutions of the less-well-known problems of infinite arrays of crossed-dipole pairs and infinite arrays of open-ended rectangular waveguides. The waveguide array solution is particularly interesting because it reduces to a set of equations which are identical to those one would use to characterize an N-port network on an admittance basis (N is the number of waveguide modes). Since the power formula is derived for a parallelogram element Lattice, the resultant solution for a specific type of element is in its most general form. Expressions for the scan-dependent, dominant mode radiation admittance and the element gain function for a multimode rectangular waveguide radiator are also derived. In addition, various aspects of the waveguide array solution are investigated in the light of previous studies of infinite arrays.     

地闪梯级先导电场波形特征研究

为研究地闪梯级先导电场波形特征,采用偶极子法结合衰减函数计算了有限大地电导率下不同距离处、不同梯级先导底部高度条件下的电场波形特征.计算结果表明:当观测点距离先导通道较近时,电场峰值随着先导通道底部高度的增大而减小;随着观测点和先导通道距离的增大,梯级先导通道底部高度对电场的影响逐步减小.对于给定高度的先导通道,其对应的电场峰值随着观测点和先导通道距离的增加,峰值先变大而后变小随着电导率的减小,先导电场波形上升时间明显增加,电场峰值衰减加快.     

Dual-beam array of microstrip leaky-wave antennas

The authors present a small series-fed array of microstrip leaky wave antennas (LWAs) operating at 6.85 GHz and showing a narrow dual-beam pattern (17°×22°). The excitation is provided by a slotted coplanar waveguide. This type of antenna could be used as a radar sensor in Janus systems for contactless measurements of velocity and distance     

An investigation of the array of circular-loop antennas

A circular-loop antenna composed ofNelements with arbitrary circumference arranged parallel in a row is analyzed by Fourier series expansion with emphasis on the existence of finite gaps at the driving points. The integral equations at the beginning are reduced to a series of linear simultaneous equations which contain only the Fourier coefficients of the electric currents of the same order. By appraising the current coefficients, the self-admittance is obtained as a sum of two parts: the finite series truncated at the number determined by the ratio of the circular-loop radius to the wire radius and the gap capacitance, and the mutual admittance is obtained as a finite series of fewer terms. Several computed curves concerning a parasitic endfire array of two elements are given, in which the computed values of the input admittance are substantiated by experiments, and radiation characteristics are examined to obtain a desirable configuration.