Numerical simulation of scattering from three-dimensional randomlyrough surfaces

Randomly rough surface patches in three dimensions are generated on the computer. The FD-TD method is used to compute scattering from surface patches by converting the Maxwell's equations into difference equations using a central difference approximation for the space and time derivatives. The volume of grids above the rough surface is divided into the total field and the scattered field regions. In between these two regions, obliquely incident waves are generated. To reduce computation, the volume of grids is chosen to be small, and a transformation is used to convert the scattered field into far zone fields for bistatic scattering coefficient calculations. Possible errors near the edge of the surface due to the use of a relatively small volume are suppressed by introducing a windowing function. Very good agreements are obtained between the results obtained by this method and those calculated by an integral equation method (IEM) for scattering from randomly rough perfectly conducting and dielectric surfaces     

A fast search method of steered response power with small-aperture microphone array for sound source localization

The Steered Response Power （SRP） method works well for sound source localization in noisy and reverberant environment. However, the large computation complexity limits its practical application. In this paper, a fast SRP search method is proposed to reduce the computational complexity using small-aperture microphone array. The proposed method inspired by the SRP spatial spectrum includes two steps： first, the proposed method estimates the azimuth of the sound source roughly and determines whether the sound source is in far field or near field; then, different fine searching operations are performed according to the sound source being in far field or near field. Ex- periments both in simulation environments and real environments have been performed to compare the localization accuracy and computation complexity of the proposed method with those of the conven- tional SRP-PHAT algorithm. The results show that, the proposed method has a comparative accuracy with the conventional SRP algorithm, and achieves a reduction of 93.62% in computation complexity compared to the conventional SRP algorithm.     

Computation of microstrip S-parameters using a CG-FFT scheme

Several open microstrip structures have been analyzed by using the conjugate gradient fast Fourier transform (CGFFT) method to solve the electric field integral equation (EFIE). The analysis of the microstrip structure provides equivalent electric currents on the conducting patches. Extensive computation is performed in the spectral domain. Windowing techniques are used to improve the accuracy of the method. New models for the microstrip feed and load have been developed in combination with the CGFFT method. Results for the S-parameters are compared with the results of other methods and with measurements. The method appears to be accurate and computationally efficient     

Front-to-back ratio of paraboloidal reflectors

An analysis is presented which uses the uniform geometrical theory of diffraction for determining the near fields diffracted by a paraboloid either with or without a conical flange attached to its circular rim when an axially propagated plane wave is incident on the concave or convex portion of the paraboloidal reflector. The field correlation theorem is used to determine the power coupled by a prime focus feed associated with the paraboloid which is being illuminated by a uniform plane wave. Based on this analysis, the front-to-back ratio of unflanged and flanged paraboloids is computed. Computed results show satisfactory agreement with the available measured as well as computed results based on alternative procedures. The variation in the on-axis gain on a prime-focus reflector when the feed is displaced from the focus is studied. Typical computed results are presented and compared with the available measured data. Computed results on the front-to-back ratio of paraboloids (flanged or unflanged) illuminated by a PFF whose radiated field exhibits phase variation over a constant radius are also presented     

Scattering from an infinite conducting cylinder covered with afinite two-layer dielectric coating (modal approach)

The electromagnetic scattering problem of a conducting infinite circular cylinder partially shielded with a finite two-layer dielectric coating has been analyzed. Cylindrical eigenfunctions with unknown modal coefficients are used to expand the interior EM fields in terms of Fourier-Bessel series. Enforcing field boundary conditions at the dielectric-dielectric interface leads to a single set of modal coefficients for field expansions inside the inner and the outer dielectric layers. Replacing the dielectric coating with the induced polarization sources and utilizing pertinent Green's functions, the dielectric-scattered fields are then formulated in terms of the modal coefficients. Imposing field equivalence conditions yields sets of linear algebraic equations for numerical computation of the unknown modal coefficients and subsequently other parameters of interest. Computed backscattered fields based on the modal technique developed are compared to experimental and numerical data obtained for the 2-D problem of a dielectric coated conducting cylinder     

Scattering from a periodic array of free-standing arbitrarily shaped perfectly conducting or resistive patches

A fast Fourier transform (FFT)-based iterative approach for computing the fields scattered by an infinite array of free-standing patches is presented. The method is capable of handling patches that are lossy and have arbitrary shape; it is useful for analyzing configurations that may not have been analyzed previously. Though a rectangular FFT is used, the formulation allows the study of the common triangular array periodicities. Results for various geometries are presented and are compared with existing results.     

Electromagnetic pulse scattered by a sphere

The magnetic field integral equation for transient electromagnetic scattering by a perfectly conducting sphere is solved by the stepping-in-time procedure. The contributions to the surface current density (SCD) from the self-patch, where the integrand is singular, and from the neighboring patches can be computed by formulas that are more accurate for these patches than the simple product used for other patches. These formulas have to include the time-derivative term of the integrand for the computation of the initial (small) values of the SCD. The improvement in the values of the scattered fields due to these corrections is significant but not dramatic.     

Research on the Radiation Characteristics of Patched Leaky Coaxial Cable by FDTD Method and Mode Expansion Method

Patched leaky coaxial cable (PLCX) is proposed as an alternative to the conventional leaky cable for wireless links in a complex environment. It is expected to have the capability of adjusting the coupling between the cable and the environment and give smoother electric field coverage. In this paper, the radiation characteristics of the PLCX with general inclined patches are studied by a hybrid method that involves the finite-difference time-domain (FDTD) method for the near-field computation and the mode expansion method for the transformation of near field to far field. In the method, the space around the patched leaky cable is divided into two regions by an artificial closed cylindrical surface that is incorporated with the FDTD lattice surface when implementing the FDTD iteration. The field distribution on the artificial surface is obtained after the implementation of the FDTD method. Meanwhile, the field outside the artificial boundary is expanded in terms of the Floquet modes with coefficients to be determined. By matching the field expressed by modes and the field obtained from the FDTD method at the artificial boundary, a matrix equation with unknown coefficients is obtained. Solving this matrix equation, the expansion coefficients are known, and the field outside the artificial boundary is ready to be obtained.     

Analysis of coplanar waveguide-fed microstrip antennas

A moment method analysis of a microstrip antenna fed by an open-end coplanar waveguide is presented. The surface electric current on the microstrip antenna is represented by the entire domain basis functions, while the surface magnetic currents in the open-end slot and in the slots of the coplanar waveguide near the open end are expanded by the subsectional roof-top basis functions. Some practical numerical aspects are carefully discussed, and a numerical device is introduced to reduce the computation time for the integrals involving roof-top basis functions and the spectral-domain Green's function. The solution accuracy is thus improved. Computed results for the reflection coefficients and input impedances are given and compared with measured values. Good agreement between theory and experiment is obtained     

Total-field absorbing boundary conditions for the time-domainelectromagnetic field equations

A method is described for generating absorbing boundary conditions (ABCs) that can be applied to the total fields rather than the usual scattered fields. As compared with the traditional use of ABCs for total-field formulations, this method has the advantages that it does not require the introduction of a mathematical connection surface between the total-field region and the scattered-field region; the total field is computed in the entire domain of computation. The incident field is accounted for by augmenting the ABC used. The resulting code is much simpler than one using ABCs for scattered fields together with a connection surface and the numerical results are much more easily interpreted since they consist of total fields only     

Etude théorique et expérimentale d’antennes plaques alimentées par couplage de proximité à une ligne microruban

In this paper a rigorous analysis and an exact computation of electromagnetically coupled microstrip antennas is presented for the case of rectangular and square patches with or without radome. The theory is based on the resolution of the integral equations by using the method of moment in conjonction with the multi-port model of microwave circuits. All of the computed results have been compared to experimental return loss made on a network analyser, and experimental radiation pattern obtained in an anechoic chamber. For a square patch antenna, ahalf wave resonant mode with a current polarisation orthogonal to that of the line current has been clearly observed when the feeding line runs along one of the edges and penetrates deeply under the patch.     

天线近场计算的卷积积分法

本文提出了一种天线近场计算的新方法，文中详细叙述了用于近场快速计算的卷积积分法，并用该方法得到了偏馈反射面天线的近场分布。文中还将该方法的计算结果与物理光学法的计算结果进行了对比，从而验证了该方法的准确性和有效性。     

Plane wave spectrum-surface integration technique for radome analysis

The purpose of this paper is to report an accurate boresight analysis for practical three-dimensional antenna-radome systems. The analysis of practical three-dimensional antenna-radome combinations has been impractical for antenna aperture areas greater than about75lambda^{2}. The principal difficulty encountered is the excessive computation time required for the large number of antenna near field calculations. The key feature of the approach taken by the authors is the use of the plane wave spectrum (PWS) formulation for calculation of the antenna near fields. The PWS formulation provides much improved efficiency over other nearfield analyses and makes this analysis possible. The method can also be applied to analyze other antenna distortion.     

Inertial snake for contour detection in ultrasonography images

Snakes, or active contour models are used extensively for image segmentation in varied fields. However, some major challenges restrict their use in many fields. The authors propose a new inertial snake model, that introduces an inertial effect of the control points into the snake framework. The proposed inertial force along with the first- and second-order continuity forces controls the spline motion through the concavities and also against weak edge forces. This smart force field, added to the inertial energy framework, posses the ability to adaptively reduce its effect near the true edges, so that the energy minimising spline converges into the edges. A greedy snake has been used for computation of the energy minimising spline. The algorithm has been tested on phantoms and ultrasound images as well. It is shown in the results that the proposed algorithm classifies the object from the background class in most of the images perfectly. Ultrasound images of a lower limb artery of an adult woman have been tested with this algorithm, and also extended for motion tracking.     

SEM representation of the early and late time fields scattered fromwire targets

In the communication, the singularity expansion method (SEM) is used to express the field scattered from an arbitrary thin-wire target. Explicit expressions are given for both the class-1 and class-2 representations of the scattered field due to step excitations. Numerical results are given for the early-time transient fields scattered from both a straight wire and a simple swept-wing aircraft model. The results of the SEM computations are compared to fields obtained by Fourier inversion techniques. It is shown that the class-2 representation yields a significant improvement over the class-1 result during the early-time interval, albeit at the expense of a more complex computation     

Dense motion estimation using regularization constraints on local parametric models

This paper presents a method for dense optical flow estimation in which the motion field within patches that result from an initial intensity segmentation is parametrized with models of different order. We propose a novel formulation which introduces regularization constraints between the model parameters of neighboring patches. In this way, we provide the additional constraints for very small patches and for patches whose intensity variation cannot sufficiently constrain the estimation of their motion parameters. In order to preserve motion discontinuities, we use robust functions as a regularization mean. We adopt a three-frame approach and control the balance between the backward and forward constraints by a real-valued direction field on which regularization constraints are applied. An iterative deterministic relaxation method is employed in order to solve the corresponding optimization problem. Experimental results show that the proposed method deals successfully with motions large in magnitude, motion discontinuities, and produces accurate piecewise-smooth motion fields.     

Radar cross section of axisymmetric objects

A method for computing the resonant region scattering by slender axisymmetric objects with arbitrary surface impedance is outlined. This method employs matching of the electric and magnetic fields on axis. Results obtained by this method have been used to generate contour maps of radar cross section (RCS) as a function of frequency and aspect. Maps for three conducting cones and a cone-spheroid covering the diameter-to-wavelength range of 0.05 to 0.70 are shown. The relationship of the high and low frequency asymptotic behavior to the mapped results is discussed. Computed and measured RCS patterns are compared.     

Visualizing near-field energy flow and radiation

Computed near-field values of Poynting's vector and electric and magnetic field intensities for a linear dipole are displayed in a way that aids visualization of the radiation process. The fields are computed for time-harmonic excitation, but are shown as a function of time to demonstrate the spatial ebb and flow of the fields around the dipole. By this means, the distinction between near and radiation fields is made clearer, and the shedding of energy by the dipole can be observed     

An FDTD/ray-tracing analysis method for wave penetration through inhomogeneous walls

A novel method of studying wave penetration through inhomogeneous walls using the hybrid technique based on combining finite-difference time-domain (FDTD) and ray tracing methods is presented . The FDTD method is used to analyze the transmission characteristics of inhomogeneous walls. Using the knowledge of the tangential electric and magnetic field distributions along the borders of the FDTD computation domain, rays are sent out to cover the rest of the environment so that prediction of signal coverage can be made more efficiently without compromising the accuracy. Numerical results of the method have been compared and shown to agree very well with those of measurement and those of full wave analysis. Examples have shown the inadequacy of the traditional ray tracing method in the presence of walls made of concrete blocks. However, the proposed method can accurately predict signal coverage by taking into account the scattered fields by the inhomogeneity inside the walls. The method does not add much to computational complexity. Reduction in computation time is even more significant when the incident waves can be approximated to be plane waves and the wall structure is periodic.     

Analysis of a thin slot discontinuity in the reference plane of amicrostrip structure

This paper presents a perturbational approach based upon the spectral domain technique for the analysis of the discontinuity effects introduced by a thin slot in the ground plane of a microstrip line. The discontinuity problem is formulated in terms of the unknown slot field by using the notion of equivalent half-space problems, using a new rigorous procedure for deriving the TE-TM decomposition of the fields and equivalent transmission line models. The perturbation current on the infinite microstrip is computed once the electric field in the slot has been derived, and an equivalent circuit for the discontinuity is obtained from this perturbation current for the low-frequency regime. Computed results are presented and compared to the measured data