地下ELF线天线在地-电离层壳体中产生的场

为了研究地震产生的机理,需要分析和研究地下任意ELF线天线在地-电离层壳体中产生的电磁场。地下任意ELF线天线产生的电磁场可由地下ELF点源产生的电磁场进行叠加。首先导出了地下ELF点源在地-电离层壳体中产生的电磁场表达式,然后得到了地下任意ELF线天线在地-电离层壳体中产生的电磁场的表达式。分别讨论了地下单条和两条ELF线天线在地面上产生电磁场的场强空间分布图,用色标表示了场强值在空间分布的强弱。电磁场的水平分量在地面上产生电磁场的场强值要比垂直分量产生的场强值大,单条线天线在地面上产生电磁场的场强值要比两条线天线产生的场强值小。     

有耗半空间时域电磁散射问题的一种混合数值模拟方法

提出了一种模拟不均匀有耗闪半空间时域电磁散射特性的混合数值方法。在自由空间用ＦＤ－ＴＤ方法，而在有耗媒质中半波动方程简化为扩散方程，并采用Ｄｕｆｏｒｔ－Ｆｒａｎｋｌｅ有限差分方法进行模拟。     

有耗介质中单极天线的场分布和SAR图

用一段刚性同轴线制作的微细单极天线在医疗上已得到广泛应用。本文给出了单极天线在有耗介质中的近场分布的数值解，进而在有耗介质中测定了温度分布和ＳＡＲ图，利用近场分布计算的ＳＡＲ图和测定和ＳＡＲ图基本相符。     

有耗介质中单极天线的场分布和SAR图

用一段刚性同轴线制作的微细单极天线在医疗上已得到广泛应用。本文给出了单极天线在有耗介质中的近场分布的数值解，进而在有耗介质中测定了温度分布和ＳＡＲ图，利用近场分布计算的ＳＡＲ图和测定的ＳＡＲ图基本相符。     

基于FDTD的二维电磁散射反演方法研究

文章针对有耗电磁介质的重建问题发展了一种新的算法.该方法在反演过程中采用常用的非线性最小二乘法来求解逆问题,通过Tikhonov正则化得到描述散射场与散射体电特性参数之间关系的迭代方程,然后将迭代方程离散化得到适于数值计算的形式,并最终实现了介质双参数的同时反演.在此基础上对有耗介质的反演进行了详细的研究,计算结果表明该方法不仅能实现介质的空间定位,在介质的电磁参数的反演上也能满足精度的要求.     

弱散射条件下半空间有耗媒质的近似重建公式

对于半空间弱有耗媒质，本文导出了用反射系数重建媒质相对介电常数和电导率剖面的近摊似反演公式，它们以解析闭式给出。     

装有金属引信的埋地介质地雷电磁散射计算

本文由等效原理推导了埋在有耗、色散土壤中的装有引信的介质地雷的电磁场积分方程,根据地雷的旋转对称特性,利用矩量法计算了半空间地雷的电磁散射,并与车载地表穿透SAR的实测数据进行了对比,两者比较一致,验证了计算方法的有效性.     

TSA增益的影响因素

文中设计了3个相同介质的超宽带渐变线天线(A、B和C),并在9 GHz～18 GHz范围内,比较了它们的增益.结果表明,渐变线天线的表面上渐变槽线以及辐射口径上场相位分布的均匀性对增益的影响很大.渐变槽线的长度D及开口宽度H分别增大到5.2倍和2.5倍,天线的增益在频段内增大了至少3.92 dB,因此渐变槽线开口方式对增益有重要影响.同时,天线辐射口径上的相位分布均匀,对于提高天线增益也是至关重要的.     

半空间模型的地下目标成像

由于电磁波在穿越不同介质时会出现折射现象,因此在对地下目标成像时,电磁波信号在穿越从雷达到达地下目标的组合通道时,路径不是直线而是折线,此时利用常规的自由空间中的合成孔径成像方法已经不能对目标进行成像。为此,基于电磁波的传播规律和地层有耗媒质的特性,提出了电磁波传输的半空间模型,使其能够充分反映电磁波信号在整个传播过程中的真实路径,并得到了相应的目标回波表达式。将其应用到机载条件下的地下目标成像之后,通过仿真比较,可以明显看出,使用半空间模型对地下目标成像效果有改善,验证了半空间模型适用于对分层土壤中的地下目标成像。     

耦合渐变槽线天线及其和差波束的矩量法分析

本文阐述一种新型渐变槽线天线（ＴＳＡ）结构,耦合渐变槽线天线ＣＴＳＡ。单片的ＣＴＳＡ除可降低副瓣电平,提高增益,改善Ｅ面Ｈ面波束的对称外,还可通过与之配合的平面印刷奇偶模双工器馈电,同时实现和差波束。本文应用空间域矩量法（ＭｏＭ）建立了分析各种ＴＳＡ结构的数值模型;该方法在没有介质基片的情况下是严重的,本文集中讨论简化ＭｏＭ中阻抗矩阵积分运算的各种技术,有效地减小了计算量,并获得较高的精度。计算结     

Wire antennas over a lossy half-space

A recently developed technique for approximate but accurate evaluation of the various vector potential components associated with a current element radiating over a lossy ground is used to study the problem of antennas radiating over a lossy ground. A general integral equation for an arbitrarily shaped thin-wire antenna over a lossy half-space is derived, and the method of moments is employed to process this equation numerically. Illustrative numerical results are presented to demonstrate the effect of the lossy half-space on a number of antenna configurations.     

A simple and accurate complex image interpretation of verticalantennas present in contiguous dielectric half-spaces

An efficient technique is developed to solve the important problem of vertical antennas located above and penetrating the interface between contiguous dielectric half-spaces. It begins by deriving the spectral expressions of the vector and scalar potential Green functions in terms of the TM wave spectral transmission coefficient. The complex image technique is used to derive simple, accurate, and rapidly convergent expressions of the full-wave spatial Green functions. The spatial Green functions are used in the moment method to model vertical thin-wire antennas residing above the penetrating the interface separating the contiguous dielectric half-spaces with and without loss     

Thin-Wire Model Using Subcellular Extensions in the Finite-Difference Time-Domain Analysis of Thin and Lossy Insulated Cylindrical Structures in Lossy Media

Recently, a subcellular thin-wire model for the finite-difference time-domain (FDTD) simulation of resistively coated cylinders with lossless insulating and surrounding media was presented. In this paper, it is shown that this model can be extended to lossy cases. The material discontinuity between lossy insulating and surrounding media is corrected as the time-domain boundary condition. The convolution term of the boundary condition is solved by employing a recursive technique. Applying the contour-path integration to the FDTD unit cells around the wire, one may find the coarse-grid-based equation with the correction term and factors for the material discontinuity and the quasi-static field behavior around the wire. In the 2-D cylindrical coordinates with rotational symmetry, the validity of the proposed model is confirmed by an impedance analysis of insulated and resistive antennas according to the electrical properties of insulating and surrounding media, as well as the choice of cell size.      

Application of wavelets on the interval to the analysis ofthin-wire antennas and scatterers

An analysis of thin-wire antennas and scatterers using orthogonal wavelets on interval [0,1] is presented. The thin-wire version of the electric-field integral equation (EFLE) is solved by the hybrid wavelet expansion and boundary element method (HWBM). Maps between the curved solution domains and the interval [0,1] are established by using the geometrical representation of the boundary element method (BEM). By virtue of these maps, bases over the curved solution domains are derived from orthogonal wavelets on [0,1] that are used to expand the unknown current over the wires. The utilization of the wavelets on [0,1] circumvents the difficulties in the application of the wavelets on the real line to finite-domain problems and has no periodicity constraint to the unknown function that is usually imposed by the periodic wavelets. Numerical examples are provided for a variety of thin-wire antennas and scatterers     

Path loss model for wireless narrowband communication above flat phantom

A new empirical path loss model for wireless communication at 2.4 GHz above a flat, lossy medium, representing human tissue, is presented. The model is valid for dipole antennas for heights up to 5 cm above the phantom and for distances up to 40 cm, and was applied to muscle and brain simulating media. For antennas placed close to the lossy medium, it was found that antenna height has a major influence on path loss. The model has been validated by measurements and simulations, which show excellent agreement     

The circumferential variation of the axial component of current in closely spaced thin-wire antennas

Closely spaced thin-wire antennas are analyzed by the moment method using the piecewise-sinusoidal function to describe the current variation along the length of the wire and a Fourier series for the circumferential variation. Data are presented for the circumferential variation of the surface current density of parallel dipoles obtained by the "thin-wire" theory, wire-grid model, and the present formulation. It is found that there is substantial circumferential variation, even for dioples spaced more than several wire diameters.     

Near-and Far-Field Thin-Wire Coupling?Theory and Expeiment

The method of moments is applied to near-and far-field coupling problems for thin-wire antennas with arbitrary orientation, excitation, and loading. A coupling matrix is derived. The analysis method is validated by the results of an extensive experimental program. Comparisons are made between theory and experiment for coupling from monopole to monopole, dipole to dipole, and dipole to dipole in the presence of parasitic elements. Special approximate formulas are developed for parallel thin-wire dipoles and monopoles. The moment methods permit accurate computation of antenna coupling in a wide variety of situations.     

Hybrid NEC/FDTD approach for analysing electrically short thin-wireantennas located in proximity of inhomogeneous scatterers

A new hybrid technique is presented which combines the method of moments with the finite difference time domain (FDTD) method to analyse electrically short, thin-wire antennas located in the vicinity of inhomogeneous dielectric bodies. The antennas are dealt with in the frequency domain using the NEC coder while the FDTD method is used to analyse the inhomogeneous part of the problem. The two sub-problems are combined by invoking the equivalence theorem     

Analysis of radiation from arbitrarily oriented wire antennas over imperfect ground (Sommerfeld formulation): SomArb

The program is for analysing radiation from antenna arrays of arbitrarily oriented thin-wire antennas over the plane surface of an imperfectly conducting earth. The solution is that obtained from the E-field integral equation by the method of moments. The effects of the imperfectly conducting earth are accounted for exactly by using the Sommerfeld formulation.     

Computation of the Impedance of an Infinitely Long Helical Transmission Line by Numerical Methods (Short Papers)

A numerical method is given for the determination of the impedance of an infinitely long thin-wire helix. The propagation constant of the current for zero tangential electric field is found and used in a variational expression for impedance. Asymptotic values of resistance versus pitch are compared with resistances of infinitely long straight-wire antennas.