Full-wave analysis of a perfectly conducting wire transmission linein a double layered conductor-backed medium

A full-wave eigenmode analysis of a waveguide structure which consists of a double layered conductor-backed medium with a perfectly conducting cylindrical wire in either the top layer or the bottom layer is presented. The analysis starts with a Fourier series representation of the total longitudinal and transverse current components on the wire surface, which are seen as the sources of the eigenmode of the waveguide. The fields generated by these sources can be expressed in terms of suitable incoming and scattered fields. Finally, Galerkin's method is used to impose the boundary conditions on the wire surface. Numerical results for a typical interconnection structure are presented     

Resonances of perfectly conducting wires and bodies of revolutionburied in a lossy dispersive half-space

The method of moments (MoM) is utilized to compute the complex resonant frequencies and modal currents of perfectly conducting wires and bodies of revolution buried in a lossy dispersive half space. To make such an analysis tractable computationally, the half-space Green's function is computed via the method of complex images, with appropriate modifications made to account for the complex frequencies characteristic of resonant modes. Results are presented for wires and bodies of revolution buried in lossy soil using frequency-dependent measured parameters for the complex permittivity, and we demonstrate that the resonant frequencies generally vary with target depth. In addition to presenting results, relevant issues are addressed concerning the numerical computation of buried-target resonant frequencies     

Scattering by a narrow perfectly conducting infinite strip in a gyroelectric medium

The scattering of a plane electromagnetic wave of wave-numberkby a perfectly conducting infinite strip of width2ais investigated for the case in which the surrounding medium is gyroelectric. The gyroelectric axis is assumed to be parallel to the edges of the strip. The problem is formulated in terms of an integral equation whose solution is obtained in the form of a series in powers ofka. Expressions for the far-zone fields and the first two terms in the series for the total scattering cross section are obtained.     

The singularity expansion method applied to perpendicular crossed wires over a perfectly conducting ground plane

The singularity expansion method (SEM) has been applied to determine natural resonances of a set of perpendicular crossed wires over a perfectly conducting ground plane. The variation of the natural resonances and the mode and coupling vectors have been studied as parameters of the system varied.     

Full-wave analysis of coupled lossy transmission lines using multiwavelet-based method of moments

Full-wave analysis for coupled lossy transmission lines with finite thickness is conducted using a multiwavelet-based method of moments (MBMM). We use the multiscalets with multiplicity r=2 as the basis and testing functions, and take the discrete Sobolev-type inner products to discretize the integral equation and its derivative at the testing points. Since the numerical integration is not needed in the testing procedure, the new approach is faster, yet preserves high accuracy due to the derivative sampling. In the new approach, we compute the incoming fields in the spatial domain directly without resorting to the inverse Fourier transform. Hence, the local coordinate system used to perform the Sommerfeld integral is avoided and the computational cost is reduced remarkably. In addition, a coarser mesh can be used owing to the smoothness of the multiscalets. Numerical examples show that the MBMM speeds up the traditional method of moments 3 /spl sim/ 10 times.     

Hybrid UTD-MM analysis of the scattering by a perfectly conducting semicircular cylinder

A hybrid UTD-MM technique which combines the uniform geometrical theory of diffraction (UTD) and the method of moments (MM) is employed to analyze efficiently the problem of electromagnetic diffraction of transverse electric (TE) and transverse magnetic (TM) waves by a perfectly conducting semicircular cylinder. An analysis of this problem is useful for understanding the coupling between the mechanisms of edge and convex surface diffraction. The accuracy of the numerical results for the far-zone fields based on this solution is established by comparison with an independent formally exact MM solution.     

Scattering by imperfectly conducting wires

An integral equation is developed for the current induced in a slender, imperfectly conducting wire of finite length by an incident plane wave. A system of linear equations is generated by enforcing the integral equation at a discrete set of points on the axis of the wire, and these equations are solved to determine the current distribution. The scattered fields and the echo area are then calculated in a straightforward manner. Numerical results are presented for the backscatter echo area of copper, platinum, and bismuth wires at the broadside aspect with lengths up to1.8lambda. These calculations show good agreement with experimental measurements. In addition, graphs are included to show the current distributions on these wires at the second resonance, the echo-area patterns for oblique incidence, and the broadside echo-area curves for perfectly conducting wires and copper wires with lengths up to3.54lambda.     

Creeping waves on a perfectly conducting cone

The rigorously formulated scalar and vector Green's functions for a perfectly conducting semi-infinite cone are approximated asymptotically to furnish the high-frequency creeping wave contributions when the source and observation points are both located on the cone surface. The results are expressed in the ray-optical format of the geometrical theory of diffraction and thus provide another canonical solution for verification of the postulates of that theory. The analytical procedure for isolating the creeping waves from other high-frequency phenomena such as tip diffraction is motivated by the methodology for the simpler circular cylinder problem, to which the present solution reduces when the cone-to-cylinder transition is performed. The results are of interest for calculation of source-induced surface currents, and of mutual coupling between slot array elements, on conical surfaces.     

Electromagnetic reverberation near a perfectly conducting boundary

We analyze the effect of an infinite planar perfectly conducting surface on the physical and statistical properties of an otherwise ideal reverberant field. The surface induces statistical uniaxial field anisotropy at a distance, and its effect can be characterized based on calculable local field polarization and anisotropy coefficients that exhibit a damped oscillatory behavior as a function of the distance to the surface. It is shown, both theoretically and experimentally, that compound exponential (CE) distribution functions with a degenerate polarization coefficient as parameter govern the statistics of the local energy density and amplitude of the vector field near the surface. The influence of adjacent walls is taken into account by a transverse field anisotropy coefficient and gives rise to bifurcation of the polarization coefficient. The effect of the transverse field anisotropy on the statistics of the energy density, field amplitude, and their sample maxima as a function of distance to the surface is quantified. It is found that the increase in the expected value of the maximum electric field strength caused by the presence of the surface is of the order of 1 dB. Theoretical results are validated against measured data. A theoretical derivation based on a spectral plane-wave expansion for this configuration is given. The results are relevant to applications in which a sensor, test artefact or critical component in immunity testing is relatively close to a conducting surface, in aperture coupling between cavities, and in emissions measurement of total radiated power.     

Inductance of perfectly conducting foils including spiral inductors

A numerical method for calculating the lumped inductance parameters of perfectly conducting foils (i.e. current sheets) is presented. A quasi-static analysis for computing the inductance for foils arbitrarily shaped in three dimensions is described. The vector current distribution on the structure is solved in terms of a scalar current potential function. The method of moments is utilized to solve the integral equation. Numerical results are also presented. The strength of this technique is that a bound on the numerical accuracy can be provided. The relative error provides not only a self-consistency check, but also the accuracy with which the numerical values have been computed. Foil structures which can be approximated accurately with a triangular patch model and whose terminal edge current distributions are known can be analyzed with this method     

Optimizing backscattering from arrays of perfectly conducting strips

Eight different numerical optimization algorithms tackled the problem of finding the best spacings for an array of perfectly conducting strips in order to get desirable backscattering characteristics. Local optimizers worked well when the problem was relatively simple and had few parameters. As the complexity of the problem increased, the genetic algorithm proved a better approach. In general, a hybrid genetic algorithm (GA) worked best, because it combined the power of the local search with a global search. This paper presents optimized results that were averaged over twenty independent runs, and discusses the pros and cons of the various approaches.     

Reduction of mutual coupling using perfectly conducting fences

A theoretical and experimental study of the use of thin perfectly conducting fences to reduce the mutual coupling of two parallel-plane waveguides radiating through a ground plane is described. The two cases which are studied areE-plane coupling of parallel planes with transverse electromagnetic mode propagation andH-plane coupling of parallel planes with the fundamental transverse electric mode propagation. The analysis presented accounts for a number of higher order modes in the waveguide apertures and uses a Fourier series approximation to the fence currents. Close agreement with experimental results is demonstrated.     

Pulsed field diffraction by a perfectly conducting wedge: aspectral theory of transients analysis

The canonical problem of pulsed field diffraction by a perfectly conducting wedge is analyzed via the spectral theory of transients (STT). In this approach the field is expressed directly in the time domain as a spectral integral of pulsed plane waves. Closed-form expressions are obtained by analytic evaluation of this integral, thereby explaining explicitly in the time domain how spectral contributions add up to construct the field. For impulsive excitation the final results are identical with those obtained previously via time-harmonic spectral integral techniques. Via the STT, the authors also derive new solutions for a finite (i.e., nonimpulsive) incident pulse. Approximate uniform diffraction functions are derived to explain the field structure near the wavefront and in various transition zones. They are the time-domain counterparts of the diffraction coefficients of the geometrical theory of diffraction (GTD) and the uniform theory of diffraction (UTD). An important feature of the STT technique is that it can-be extended to solve the problem of wedge diffraction of pulsed beam fields (i.e., space-time wavepackets)     

Adaptive multiscale moment method (AMMM) for analysis of scatteringfrom perfectly conducting plates

Adaptive multiscale moment method (AMMM) is presented for the analysis of scattering from a thin perfectly conducting plate. This algorithm employs the conventional moment method and a special matrix transformation, which is derived from the tensor products of the two one-dimensional (1-D) multiscale triangular basis functions that are used for expansion and testing functions in the conventional moment method. The special feature of these new basis functions introduced through this transformation is that they are orthogonal at the same scale except at the initial scale and not between scales. From one scale to another scale, the initial estimate for the solution can be predicted using this multiscale technique. Hence, the compression is applied directly to the solution and the size of the linear equations to be solved is reduced, thereby improving the efficiency of the conventional moment method. The basic difference between this methodology and the other techniques that have been presented so far is that we apply the compression not to the impedance matrix, but to the solution itself directly using an iterative solution methodology. The extrapolated results at the higher scale thus provide a good initial guess for the iterative method. Typically, when the number of unknowns exceeds a few thousand unknowns, the matrix solution time exceeds generally the matrix fill time. Hence, the goal of this method is directed in solving electrically larger problems, where the matrix solution time is of concern. Two numerical results are presented, which demonstrate that the AMMM is a useful method to analyze scattering from perfectly conducting plates     

Microwave density imaging of perfectly conducting objects in thenear-field region

Analytical and numerical studies of microwave diversity imaging of continuous and discrete conducting objects in the near-field region are presented. Analytical results show that the image of the scattering object can be reconstructed by Fourier inversion of the data acquired from the recorded scattered field using angular and frequency diversity techniques. Different feature information of the scattering object can be obtained using a polarization diversity technique. Various scattering arrangements are studied and compared on the basis of the reconstructed image quality and practical considerations. Numerical results show that the described frequency, angular, and polarization diversity techniques in the backward scattering arrangement can result in a cost-effective approach in near-field microwave imaging systems     

Frequency swept tomographic imaging of three-dimensional perfectly conducting objects

The use of frequency swept or frequency diversity techniques to achieve, superresolution in the imaging of three-dimensional perfectly conducting objects is studied and demonstrated by computer simulations. The frequency swept imaging concept is found to be a generalization of the inverse scattering theory. By invoking Fourier domain projection theorems, it is demonstrated analytically that images of separate slices of three-dimensional targets can be obtained, thus establishing the feasibility of a tomographic radar. Computer simulation results that verify these theories for extended and composite point scattering objects are presented.     

The echo area of a perfectly conducting prolate spheroid

An approximate general solution for the electromagnetic backscattering by a perfectly conducting prolate spheroid is derived. The solution is obtained from an estimate of the solution to a transient scattering problem which is deduced, in part, from the known time-dependent backscattered waveform for a perfectly conducting sphere. From the analysis the echo signal as a function of the source frequency for arbitrary orientation of the spheroid and arbitrary linear polarization of the incident plane electromagnetic wave can be predicted in the resonance region. Calculated results for a 2:1 axial ratio spheroid are compared with experimental data for two principal polarizations and major axes ranging from 0.32 to 1.59 wavelengths.     

Broadside radar cross section of the perfectly conducting cube

The broadside radar cross section (RCS) of the perfectly conducting cube is predicted from arbitrarily low to arbitrarily high frequencies, and compared to measured data taken for cube side lengths ranging from 0.15 to 4 wavelengths. The predicted and measured RCS curves agree to within the estimated experimental limits of accuracy ofpm 1dB. At low frequencies the magnetic-field integral equation was "augmented" to eliminate its spurious homogeneous solutions and thus to produce high accuracy beyond the resonance region up through the intermediate frequency range. At high frequencies the conventional diffraction solution was "enhanced" to produce high accuracy down through the intermediate frequency range into the resonance region. Close agreement between these two very different theoretical solutions in the intermediate frequency range confirmed the validity of each solution and permitted calculation of reliable curves for the amplitude and phase of the backscattered far field versus frequency.     

Full-wave analysis of quasi-optical structures

A full-wave moment method implementation, using a combination of spatial and spectral domains, is developed for the analysis of quasi-optical systems. An electric field dyadic Green's function, including resonant and nonresonant terms corresponding to coupling from modal and nonmodal fields, is employed in a Galerkin routine. The dyadic Green's function is derived by separately considering paraxial and nonparaxial fields and is much easier to develop than a mixed, scalar and vector, potential Green's function. The driving point impedance of several antenna elements in a quasi-optical open cavity resonator and a 3×3 grid in free space are computed and compared with measurements