Analysis of a wire antenna in the presence of a body of revolution

The problem of an arbitrarily oriented thin-wire antenna located near a body of revolution is analyzed. The usual integrodifferential equation for a thin wire in unbounded space is generalized to account for scattering from the nearby body. The presence of the body is accounted for by a numerical dyadic Green's function. The modified wire equation is solved by standard numerical techniques to obtain the current distribution on the wire. The effects of various bodies on input admittance are compared with results for an isolated antenna. Measured and theoretical input admittance data for a monopole near several different bodies of revolution are found to be in good agreement.     

An efficient method for the analysis of a structure comprising an appendage attached to a planar surface of a conducting body

A technique is presented to efficiently solve for the currents on an appendage, e.g., antenna, attached to a planar surface of a conducting body. The appendage may be embedded in a homogeneous, dielectric material. The technique presented alleviates the complications associated with the point where the appendage is attached to the body. To illustrate the method, a wire antenna attached to an axisymmetric body is analyzed in detail. A set of coupled integral equations are formulated, appropriate quantities are expanded into Fourier modes, and coupled integral equations are derived for the Fourier coefficients of the unknowns. These equations are solved and the input admittance of the wire antenna is determined from the computed currents and is corroborated by measurements.     

Integral equation analysis of a sheet impedance coated window slotantenna

Presents an integral equation and method of moments analysis of a window slot antenna. The antenna is modeled by a sheet admittance coated rectangular aperture in an infinite ground plane. It is shown that the sheet admittance coated aperture is complementary to a sheet impedance plate, which permits the window slot antenna to be analyzed with existing computer programs. Numerical results are compared with measurements for input impedance and radiation efficiency     

Terminal admittance of a thin biconical antenna in an isotropic compressible plasma

An exact expression has been derived for the terminal admittance of a thin biconical antenna in an isotropic compressible plasma. It is assumed that the ion sheath is a sphere whose radius is equal to the halflength of the antenna.     

Frequency characterization of a thin linear antenna using diakopticantenna theory

A frequency-dependent analytical expression for the input impedance of a thin wire antenna is obtained using diakoptic theory. The linear antenna is diakopted into electrically short segments, where each is treated as a component with two terminals (except for end pieces, which have only one terminal). An impedance matrix is found which characterizes coupling between all segments. By expanding the free-space Green's function in a power series in wavenumber k, each entry in the resultant impedance matrix is obtained as an explicit function of frequency. The input admittance is found as a ratio of two polynomials in wavenumber k. A more systematic approach for the solution of the input admittance is achieved by expanding both the unknown current vector and the Green's function in power series in k. Equating coefficients of like powers in k leads to a numerically efficient algorithm which is used to determine the input admittance as a function of frequency. Numerical results compare well with the input impedance obtained from a conventional integral equation solution     

The Analysis of Monopole Antennas Located on a Spherical Vehicle: Part 2, Numerical and Experimental Results

Presented are various numerical results illustrating the behavior of thin monopole antennas located on a perfectly conducting sphere. The method of analysis, described in a previous paper, uses an integral equation solution for the unknown wire currents, and a modified Green's function to limit the range of integration to over the wires only. Studies are made of the input quantities, radiated currents and induced sphere currents for various antenna geometries. A comparison of the computed input impedance of monopole on the sphere is made with experimental data and good agreement is noted.     

Modélisation d’une antenne-réseau et traitement optimal

An array antenna is modeled after a linear multipole filter, one part of which is connected to a distant source, radiating in a specified direction, while the relations between the other parts are characterized by the antenna admittance matrix. This modeling technique is applied to an array of parallel linear wire antennas. It is shown how the array admittance matrix can be evaluated numerically by a discrete quantization of the Maxwell’s equations with the proper boundary conditions (Harrington’s method of moments). The admittance matrix is then used to formulate the optimum signal processing for transmission (maximization of antenna gain, with or without constraints) and for reception (maximization of signalto-noise ratio). Along with the model of the array antenna that is submitted, a method of signal processing is developed in which accurate estimates are included of the losses that occur within the array elements as well as of the coupling between elements and of the noise arising in the receiving system. The antenna designer can thus optimize the geometric configuration of the array and study the phenomenon of superdirectivity with a more realistic approach than was hitherto possible.     

平面波展开结合矩量法分析频率选择表面

为了快速分析频率选择表面（FSS）,利用天线阵列理论,引入FSS单元之间互导纳的概念,得到互导纳方程。当FSS阵列无限大时,可以应用Floquet定理简化该方程,同时对方程中某些收敛较慢的项进行平面渡展开,利用矩量法求解。采用该思路我们计算了几种多层FSS及多频FSS,并和实测结果进行对比,得到了较满意的结果。不仅如此,该方法相对其他的单一数值方法具有速度快、收敛好的特点。     

On the Pulse Response of a Flush-Mounted Coaxial Aperture

The radiation field pattern of a flush-mounted coaxial aperture is derived in the frequency domain. By using the Lorentz reciprocity theorem, the equivalent current generator is obtained which drives the apparent annular antenna admittance in shunt with the load admittance. The current source, aperture admittance, and load admittance determine the transfer function. The transfer function multiplied by the expression for the spectrum of the incident pulse forms the integrand of the Fourier transform from which the time history of the current waveform in the load admittance may be obtained using a computer. There are several applications of the theory. The one of dominant interest at present may be described as follows. A coaxial transmission line terminated in a known load admittance is located in the interior of a missile. The free end of the cable forms an aperture antenna at the skin of the missile, i.e., at the normal junction of coaxial connectors. The problem is to determine the time history of the current in the load admittance when an intense transient electromagnetic field impinges on the receiving antenna. Very accurate numerical results may be obtained from this theory provided the ground plane is sufficiently large and certain dimensional limitations on the sizes of the inner conductor and sheath of the coaxial aperture (expressed in terms of the wavelength) are met.     

Measurement techniques for antennas in dissipative media

Methods used to simulate dissipative media environments for antennas are reported and special techniques developed to determine the electrical properties of antennas in such media are discussed. Tank systems for simulating infinite homogeneous isotropic media characterized by ratios ofalpha/betain the range0 < alpha/beta < 1.0are described along with the apparatus for determining the constitutive parameterssigmaandepsilonof the media. A new device for measuring antenna input admittance is presented which permits a simple measurement of admittance over a broad frequency range where conventional methods are cumbersome in field use. Apparatus for measuring antenna current and charge distributions is described together with a discussion of the associated probing errors. Measured admittances and current and charge distributions are compared with current theories for thin wire linear and loop antennas in the dissipative media and are found to be in good agreement.     

Linear transmission-line model analysis of arbitrary-shape patch antennas

A quasi-TEM lossy transmission-line model is used to express the radiation admittance of an arbitrary-shape symmetrical patch antenna which is linearly polarised. The then retical admittance is obtained from the solution of a Riccati differential general equation.     

A numerical solution for the near and far fields of an annular ring of magnetic current

A simple method for calculating the near and far zone fields from an annular ring of circumferentially directed magnetic current which may be used to represent coaxial apertures is presented. Near-field contours are given for two ring sizes. The utility of the method has been illustrated by its application in several practical antenna problems where the magnetic ring current serves as the primary source. Among these are the analysis of dipole antennas mounted on a conducting sphere or cylinder, the impedance of a coaxially fed Yagi-Uda antenna, a coaxially driven wire loop, and the radiation from a coaxial aperture at the base of a cone.     

Application of on-surface MEI method on wire antennas

The formulas of the on-surface measured equation of invariance (OSMEI) for wire antennas are derived. The unknowns of each node on the antenna surface are expressed by the vector potential function and surface current density. The unknowns in the vicinity of each node are coupled in a linear equation and the coefficients of the linear equation are determined by the measured equation of invariance (MEI) method. The final impedance matrix obtained by the OSMEI is a highly sparse matrix. It demonstrates that the currents on thin wire antennas may also be solved by a differential equation-based formulation in addition to the conventional integral equations     

Numerical analysis of arbitrarily shaped probe-excited single-armprinted wire antennas

A general integral equation technique is described for analysis of an arbitrarily shaped single-arm printed wire antenna excited through a vertical probe. A unified current integral equation is formulated on the basis of dyadic Green's functions and the reciprocity theorem. The current distribution is obtained by using a parametric moment method in which parameter segments are adopted for the printed wire instead of the commonly employed wire length segments. The radiation field solution involving both the printed antenna and vertical probe is also presented. The validity of the formulation is verified by comparing the numerically obtained input impedance and radiation patterns for a linear antenna and a meander antenna with measured data. A circular open loop and an Archimedian spiral are investigated to illustrate the applicability of the present technique     

The Analysis of Monopole Antennas Located on a Spherical Vehicle: Part 1, Theory

In this paper, a technique for determining the behavior of thin-wire antennas mounted radially on a conducting sphere is formulated. The method of analysis involves the derivation of an integral equation for the antenna current. By a proper choice of boundary conditions, a modified Green's tensor for the sphere can be defined. This limits the range of the integral equation to over the thin wires only, thereby permitting a relatively simple solution for the antenna currents.     

Resonance of a wire antenna near the lower hybrid frequency in an RF-generated magnetoplasma

The lower hybrid resonance (LHR) of a wire antenna immersed in an RF-generated laboratory plasma was observed with a frequency sweeping admittance bridge. It is shown that the resonance frequency observed in the experiment agrees with the LHR frequency calculated from an ion density and a static magnetic field intensity.     

Corrugated spherical antenna

The radiation characteristics of a corrugated metallic sphere with an azimuthal slot are studied. For the purpose of analysis, a dielectric coating equivalent to the corrugation on the surface is assumed. Expressions for the equivalent relative permittivity, input admittance, gain and radiated far field, based on the boundary-value approach, are presented. For a spherical antenna of k0a = 4.9087 with corrugation corresponding to an equivalent dielectric coating of relative permittivity 8.36, it is shown that the increase in gain over the uncorrugated antenna is 6.15 dB. The above antenna was fabricated and the experimental pattern obtained is compared with the theoretical result.     

Theory of a vertical tubular antenna located above a conducting half-space

The input admittance and the current distribution of a finite vertical tubular dipole antenna located above an infinite dissipative half-space can be found as a function of the distance above and the electric properties of the dissipative half-space. An integral equation for the current on the surface of the antenna is formulated and subsequently solved by numerical evaluation of associated moment functions in the Fourier transform plane. The magnitude, but not the distribution, of the current is found to be strongly affected by the presence of the dissipative medium. At certain distances above the half-space, the input conductance of the antenna reaches its maximum value.     

FAFFA加速的PO-MM研究复杂金属载体上线天线电磁特性

本文提出了一种快速远场近似(FAFFA)加速的混合物理光学矩量法(POMM),利用FAFFA加速计算矩阵方程中的矩阵矢量积,明显提高了计算效率.对物体表面上的远场组之间的耦合作用推导出了一组简洁的计算公式,并分析了计算复杂度.复杂金属组合体上线天线输入导纳、互导纳和方向性图的计算结果与文献结果一致.利用该方法分析计算了一个舰船模型上线天线的电磁特性.数值结果表明了这种方法的正确性和工程应用中的有效性.     

VOLMAX: a solid-model-based, transient volumetric Maxwell solverusing hybrid grids

This paper provides an overview of the finite-volume algorithm, the dissipative time-integration scheme, boundary condition implementation, grid generation, and a time-step definition suitable for sub-time cycling. To examine the accuracy of VOLMAX operating in either a purely unstructured or a hybrid-grid mode, the resonances of a rectangular cavity, the input admittance of a “thick” wire antenna, and three simple microstrip applications (microstrip line, patch antenna and low pass filter) with well-known FDTD solutions are examined. The latter three examples demonstrate the accuracy that can be obtained by launching microstrip-guided waves on cubical hexahedral (FDTD) grids and through a dense, unstructured linear tetrahedral region