Mutual coupling in aperture-coupled patches on cylindrical reflectors calculated using a spectrum of two-dimensional solutions

The mutual coupling between groundplane slots in aperture-coupled patch antennas on cylindrical structures is calculated using a moment method in the Fourier domain. By separating the three-dimensional (3D) problem into a spectrum of two-dimensional (2D) problems an efficient calculation of the admittance is possible. To increase the accuracy in the mutual admittance calculation, an asymptotic extraction technique is used. Several cases of antenna geometry are investigated and comparison is made to measurements. The method used allows for efficient and accurate analysis of dual polarized aperture-coupled patches placed on general cylindrical structures, as in the case of base-station antenna arrays for mobile communications.     

A fast algorithm for calculating the radiation pattern in the longitudinal plane of antennas with cylindrical structure by applying asymptotic waveform evaluation in a spectrum of two-dimensional solutions

When dealing with electromagnetic problems of small three-dimensional (3-D) elements, such as dipole, microstrip patches and slots, in the vicinity of two-dimensional (2-D) structures, it is very efficient to find the radiation characteristics of the 3-D elements by using a spectrum of 2-D solutions (S2DS). Only one 2-D solution in the spectral domain is needed to obtain the radiation pattern in the transverse plane defined by /spl theta/=90/spl deg/. For the radiation in a longitudinal plane defined by a fixed azimuth angle /spl phi/, one 2-D problem has to be solved for each value of the polar angle /spl theta/. This paper presents a fast algorithm by which the radiation pattern in the longitudinal plane can be computed more efficiently. The algorithm applies the method of asymptotic waveform evaluation (AWE) in the 2-D spectral domain. For the cases shown in the paper, the algorithm needs only three 2-D solutions to determine the complete radiation pattern in the longitudinal plane.     

Impulse responses of two-dimensional antennas

On the basis of the equation of the Fresnel-Kirchhoff scalar diffraction field, the impulse responses of parallel-fed and series-fed rectangular antennas with separable aperture distributions and the impulse responses of parallel-fed and center-series-fed circular antennas with circularly symmetric distributions are derived—all of them can be expressed in the aperture amplitude distributions.     

Crosspolarisation characteristics of cylindrical triangularmicrostrip antennas

Crosspolarisation characteristics of triangular microstrip antennas mounted on a cylindrical body are studied using a full-wave analysis. Numerical results of the far-zone copolarised and crosspolarised radiated fields at the TM₁₀ mode for different cylinder radii and flare angles are calculated and analysed. A significant dependence of the crosspolarisation level on the cylinder radius and flare angle is observed. Details of the results are presented     

Transient fields of thin cylindrical antennas

The time variation of the radiation field of a thin cylindrical antenna driven by a dc pulse is investigated theoretically. Computed values of the radiation field are presented graphically for successive instants of time as a function of the angle between the antenna axis and the position vector of the distant point in space and for different angles as a function of time.     

Admittance of an isolated waveguide-fed slot radiating betweenbaffles using a spectrum of two-dimensional solutions

An efficient method of computing resonant length and admittance characteristics of an isolated broad-wall shunt slot radiating between baffles of finite height is presented. The outer three-dimensional (3D) field problem associated with this geometry is reduced to a two-dimensional (2D) one via a Fourier transformation with respect to the longitudinal z direction. For each value of the longitudinal wave number k_z an integral equation is solved for the E field in the mouth of the plates using the method of moments. This procedure is repeated for several discrete values of k_z, to obtain a spectrum of 2D solutions which are then inverse-transformed to construct the 3D solution in the spatial domain for the exterior baffle region and the half space. The slot aperture field is determined by the conventional moment method solution to the integral equation that enforces the continuity of the H field across the slot. Scattering properties of the slot are then deduced. Numerical results for the resonant length and resonant conductance are presented. Computer results are found to be in good agreement with experimentally measured data     

Simultaneous time and frequency domain solutions of EM problemsusing finite element and CFH techniques

This paper describes an efficient method for both time- and frequency-domain solutions of electromagnetic (EM) field problems. In this method EM field problems are formulated using Laplace-domain finite element approach and are solved using complex frequency hopping (CFH) technique. CFH is a moment-matching technique which has been used successfully in the circuit simulation area for solution of large set of ordinary differential equations. Problems consisting of Dirichlet, Neumann and combined boundary conditions can be solved using the proposed algorithm to obtain both time and frequency responses. Several electromagnetic field problems have been studied using the new technique and the speed-up advantage (one to three orders of magnitude) compared to conventional finite element technique is demonstrated. A good agreement between numerical results obtained using the proposed method and the previously published results has been found     

Electric fields and vector potentials of thin cylindrical antennas

The vector potential and elastic field generated by the current in a center-driven or parasitic dipole antenna that extends from z=-h to z=h are investigated for each of the several components of the current. These include sin k (h-|z|), sin k|z|-sin kh , cos kz-cos kh, and cos kz/2-cos kh /2. Of special interest are the interactions among the variously spaced elements in parallel, nonstaggered arrays. These depend on the mutual vector potentials. It is shown that at a radial distance ρ~ h and in the range -h⩽z⩽h, the vector potentials due to all four components become alike and have an approximately plane-wave form. Simple approximate formulas for the electric fields and vector potentials generated by each of the four distributions are derived and compared with the exact results. The application of the new formulas to large arrays is discussed     

Hybrid finite-element methodologies for antennas and scattering

This paper is an overview of the finite-element method (FEM) as applied to electromagnetic scattering and radiation problems. A brief review of the methodology is given with particular emphasis on new developments over the past five years relating to feed modeling, parallelization, and mesh truncation. New applications which illustrate the method's capabilities, versatility, and utility for general purpose application are discussed     

Analysis of tilted-coil eccentric borehole antennas in cylindrical multilayered formations for well-logging applications

Well-logging tools employing tilted coil antennas have been proposed to provide directional (azimuth) information and improved estimates of anisotropy when compared to conventional tools that use horizontal coils. In this paper, we analyze the response of logging tools with tilted coil antennas in eccentric boreholes crossing cylindrical multilayered formations (earth formations with invasion zones) by two approaches. The first approach is based on a pseudoanalytic formulation, previously applied for concentric boreholes and extended here to include eccentric boreholes. The second approach is based on three-dimensional (3-D) numerical simulations using the finite-difference time-domain (FDTD) algorithm extended to cylindrical coordinates and incorporating cylindrical perfectly matched layers (PML). The results from the two formulations are compared for different formations, showing very good agreement.     

Linkage between two microwave antennas in the presence of a cylindrical reflector

It is shown how it is possible to calculate the damping of a microwave scattered by a cylinder and a plane which contains the transmitting and receiving antennas. Experiments agree very well with theory.     

Analysis of scattering by a large array of waveguide-fed wide-slot millimeter wave antennas using precorrected-FFT algorithm

An effective numerical technique employing the precorrected-fast Fourier transform (P-FFT) technique based on the method-of-moments (MoM) is presented to study the scattering from wide-slot antennas fed by waveguides with arbitrary terminations. As the Rao-Wilton-Glisson (RWG) functions are used as the basis and testing functions, the magnetic currents with arbitrary slot directions are considered. In addition, the P-FFT technique is employed to accelerate the MoM procedure for a large slot array. The numerical results are obtained and compared with both the traditional MoM results obtained using the entire-domain basis functions and the experiments results, to demonstrate better effectiveness and accuracy of this technique for millimeter wave scattering from arbitrary wide-slot antennas.     

柱形量子点的电子拉曼散射研究

本文对CdS柱形量子点的电子拉曼散射进行了研究;推导了拉曼散射截面的表达式,给出了有关的选择定则,获得了丰富的拉曼散射谱线并对谱线特点进行了分析和讨论,讨论结果直接给出了电子的有关信息。     

Analysis of two-dimensional electromagnetic scattering fromnonplanar periodic surfaces using a strip current model

A method-of-moments solution is presented for the problem of two-dimensional transverse magnetic (TM) scattering of a plane wave from a nonplanar periodic surface separating two contrasting homogeneous media. The moment solution uses fictitious spatially periodic and properly modulated electric current strips to simulate the field scattered by the surface and the field penetrating the surface. The fields radiated by the current strips are represented in terms of Floquet modes, and the problem is reduced to a consideration of the fields over a single period. The simulated fields are forced to obey the continuity conditions for the tangential components of the electric and magnetic fields at a selected set of points on the interface within a single period. The procedure is simple to implement, rapidly converging, and applicable to arbitrary smooth profiles. Perfectly conducting media are treated as reduced cases of the general procedure for penetrable media. Results for sinusoidal surfaces are given and compared with available data. The efficiency of the method is demonstrated     

Application of moment method to large cylindrical reflector antennas

For a cylindrical reflector, illuminated by a line source, the induced surface current is assumed as the sum of the physical optics and an unknown difference current. This difference current is then found by an application of the moment method. It is shown that such an assumption increases the accuracy of the computations and reduces the required computer time.     

Transmitting, receiving, and scattering properties of antennas

In most modern textbooks on antennas, it is stated that receiving antennas scatter as much as they absorb under matched-load conditions. This is incorrect, as was shown 50 years ago. The reason for this discrepancy is an apparently incorrect use of the equivalent circuits. In this tutorial paper, a simple example of a two-element Yagi antenna and a test dipole in the far field is analyzed for transmission, reception, and scattering, through the use of the symmetric impedance matrix. It is shown that the correct equivalent circuit for the scattering case is more complicated, owing to the existence of more sources than in the transmitting case. Through a numerical example, it is also shown that the scattered power may be larger, equal to, or smaller than the absorbed power.     

Measurement of self and mutul impedances of two coupled cylindrical antennas in a hot plasma

The self and mutual impedances of two coupled cylindrical antennas embedded in a hot plasma have been measured. A large volume of hot plasma was provided by a mercury-arc discharge. Pairs of monopoles with various lengths were embedded in the plasma volume and excited by r.f. signals. The experimental results show that, near the plasma frequency, the self and mutual impedances undergo rapid changes as the plasma density is varied. The effect of an electroacoustic wave on the self impedance is not very outstanding. However, this wave has a significant effect on the mutual impedance, as can be evidenced by the appearance of electroacoustic resonances (Tonks-Dattner resonances) in the mutual-impedance curves.