Integral equation solution and RCS computation of a thin rectangular plate

In this work, a new integral equation is employed to calculate the current distribution on a rectangular plate which is illuminated by a plane wave. Numerical results are also obtained for the radar cross section (RCS) of the plate for different angles of incidence and different dimensions of the plate. These results are compared with other RCS computations using geometrical theory of diffraction, physical optics, and variational methods.     

Radiation from a flanged rectangular waveguide

The radiation from a rectangular waveguide with a perfectly conducting infinite flange is rigorously studied by using the method of the Kobayashi potential (KP). The fields in the waveguide and half-space are expanded in terms of the waveguide modes and the Weber-Schafheitlin discontinuous integrals, respectively. Continuity of the tangential aperture fields yields matrix equations for the expansion coefficients and the matrix elements consist of double infinite integrals and double infinite series of Bessel functions, which are calculated efficiently by applying the asymptotic approximation of the Bessel function. Numerical results are presented for various physical quantities, such as the aperture admittance, reflection coefficient of the incident wave, and magnitudes of higher-order mode waves, as well as the far-radiation pattern and aperture fields. To verify the validity of our method, the results are compared with other methods and excellent agreement is obtained.     

Analysis of the zonal and rectangular slots on a conductingspherical cavity

The zonal slot cut on a conducting spherical cavity is analyzed rigorously. The slot is excited asymmetrically, which excites higher order azimuthal modes. The Green's function approach is used to formulate an integral equation for the magnetic current in the slot, which is solved using the moment method (MoM). New recurrence formulas are derived so that within their stable region the admittance integrals can be evaluated without the need for any numerical integration. In this case, the solution is very easy to implement with extremely short computation time. The effects of the latitude angle on the peak resistance and percentage bandwidth are investigated. Furthermore, the cavity resonance modes and their degeneracy are examined by plotting the expansion coefficients of the magnetic current. In addition, the problem of a rectangular slot in the nonequatorial plane is also studied. Measurements are carried out and good agreement between theory and experiment is obtained     

预测反射面天线馈源毁伤效应的混合算法

提出了一种预测反射面天线系统在馈源毁伤状态下辐射特性的混合算法.采用时域有限差分法(FDTD)分析了波导开口辐射器馈源穿孔毁伤时的初级辐射特性,利用物理光学法(PO)和物理绕射理论(PTD)分析了反射面天线的次级辐射特性.并采用非场分裂式完全匹配层(UPML)吸收边界条件、共形网格(Conformalmesh)技术提高计算精度和效率,取得了良好的效果,充分验证了混合算法的有效性.     

Complex images of a point charge in rectangular conducting planes

The exact images of a point charge in rectangular conducting planes are discretely located on an infinite plane, making it difficult to compute the electrostatic field rapidly. In the paper, a complex image theory for the electrostatic problem in rectangular conducting planes is investigated. The research shows that only a few complex images are used to replace the countless exact images, but the error is less than 0.2% when they are utilized to compute the electrostatic potential functions, and the execution time is greatly reduced     

A compact RCS formula for a dihedral corner reflector at arbitraryaspect angles

A compact closed-form formula for the RCS of a perfectly conducting right dihedral corner reflector at arbitrary aspect angles is presented. The approach is based on a combination of ray tracing, physical optics (PO), and the physical theory of diffraction (PTD). There is good agreement between the results obtained using the closed-form formula and those obtained by the shooting and bouncing rays (SBR) technique     

Une approche spectrale de la théorie physique de la diffraction

This paper presents a new method of approach to the solution of the problem of the diffraction of electromagnetic waves, by perfectly conducting plane obstacles, which is developped from an equivalence between the Kirchhoff’s integral and the continuous spectrum plane waves, established by E. Durand The formalism used for the determination of the diffracted field correspond to a generalisation of the physical optics approximation. One adds to the elementary term of the physical optics, the successive edge effects. The complete development of the field is a spectral integral whose weight function is obtained from the analytical expression of the illuminated contourof the obstacle, in the spectral domain, which is connected to the incident field on the obstacle. The diffraction coefficients and the edge waves are revealed which permits a good physical visualisation of the diffraction phenomena. The method is presented on classical case of the two-dimensional infinitely thin strip. It is also applied to the strips grating, and generalisated to three dimensional problems for the rectangular plate, the plates grating, and the circular and elliptical discs.     

Diffraction by a rectangular groove with resistive walls

The plane wave diffraction from a rectangular groove having resistive vertical walls with material loading is analyzed for E polarization by using the Fourier transform technique. The problem is formulated into a modified Wiener–Hopf equation applying boundary conditions. The modified Wiener–Hopf equation is solved via the factorization and decomposition procedure. The scattered field is evaluated by taking the inverse Fourier transform and applying the saddle point method. Numerical results on the backscatter radar cross-section (RCS) patterns are presented for various physical parameters.     

Radiation from a waveguide-backed aperture in an infinite ground plane in the presence of a thin conducting plate

Coupled integrodifferential equations are formulated for the general problem of radiation from a waveguide-backed aperture in an infinite conducting plane when a thin, finite, and arbitrarily oriented conducting plate is located in its proximity. The general equations are particularized for the special case of a rectangular aperture and a rectangular plate and solved numerically using the method of moments. Detailed data are presented and discussed for various quantities of interest.     

Scattering characteristics of a rectangular groove in a reactivesurface

The diffraction of a plane electromagnetic wave by a rectangular groove in a reactive plane is studied rigorously through the Fourier transform technique. The corresponding boundary value problem is formulated into a modified Wiener-Hopf equation of the third kind whose approximate solution involves two sets of infinite number of unknown constants satisfying two infinite systems of linear algebraic equations. Numerical solutions of these systems are obtained for various values of the surface reactance and the sizes of the groove through which the effects of these parameters on the diffraction phenomenon are studied     

Ray tracing with PO/PTD for RCS modeling of large complex objects

The present paper deals with a new efficient approach in order to assess the simulation of scattered fields from arbitrary metallic objects. The basic idea is to combine a ray tracing algorithm with the principles of physical optics (PO) and the physical theory of diffraction (PTD). The ray tracing algorithm stochastically launches discrete rays and uses a ray density normalization. In order to perform simulations at finite objects the PO/PTD formulation is required. Thus, fast intersection routines can be implemented, while the ray density formulation reduces the PO and PTD integrals to a pure sum of ray contributions. Simulation results obtained with this model are verified by comparison with both exact simulations using a method of moments (MoM) code and measurement results, proving an excellent accuracy and fast computation even at complex objects. With this asymptotic approach, scattering properties of large objects that are too complex for exact methods can be analyzed with rather moderate computation efforts. Typical applications include the simulation of low observability (LO) designs as well as the generation of databases for identifying unknown aircraft by their radar signature.     

Aperture admittance of a rectangular aperture and its use

It has been found that a rectangular aperture not more than one wavelength long in a conducting plane can be characterized by two complex numbers (called the aperture admittances) for the regions on each side of the aperture for the purpose of obtaining an accurate estimate of the tangential electric field inside the aperture. To define these admittances, the aperture is closed with an infinitesimally thin perfectly conducting plate. The aperture admittance for the region on one side of the aperture is that of the magnetic current sheet M₀ placed on this side of the plate. The aperture admittance for the region on the other side of the aperture is that of M₀ placed on the other side of the plate. M₀ is parallel to one of the long edges of the aperture, and along this edge is a simple half-cycle of a sinusoid. M₀ is independent of the coordinate that is measured along the width of the aperture     

The mutual coupling and diffraction effects on the performance of aCMA adaptive array

The performance of the constant modulus algorithm (CMA) with the steepest descent method used in an adaptive array of monopole antennas mounted on a rectangular conducting plate was investigated. The mutual coupling (MC) effect among the array elements and the diffraction effect caused by the conducting plate were taken into account in the calculation by a hybrid method of moment method (MM) and geometrical theory of diffraction (GTD). Simulations showed that the CMA adaptive array performs differently when the MC and the diffraction effects are taken into account. In some cases, the speed of convergence is slower with MC, and in other cases it is faster. Also, in multipath scenarios the array sometimes converges on a weaker delayed ray rather than the direct ray when MC is included. The capture property is explained by the fact that the CMA algorithm is sensitive to initial conditions and the initial array pattern is directional due to MC-not omnidirectional as in the ideal case. The performance of the array on a finite ground plane is different from that on an infinite ground plane due to diffraction effects     

Enhanced electromagnetic transmission through a slit surrounded by rectangular grooves

Electromagnetic transmission through a slit surrounded by rectangular grooves in a conducting plane is investigated. An electromagnetic boundary-value problem associated with a slit surrounded by rectangular grooves in a conducting plane is rigorously solved based on the Fourier transform, eigenfunction expansion and mode matching method. The transmission coefficient through the slit is represented in a series. Computation is performed to illustrate the effect of the groove geometry on the transmission behaviours.     

Electromagnetic Diffraction by a Planar Array of Circular Disks

The diffraction of a plane electromagnetic wave by a planar rectangular array of perfectly conducting circular disks is considered. The diffracted field is calculated from the induced electric and magnetic dipole moments and higher-order multipole moments. Static and dynamic interactions between the induced dipole moments are being considered, first by using a plane-wave approximation for the dipole fields (for cases where the separation of the disks is large compared with the wavelength) and then by calculating the actual fields at each disk. The formulas are applied to calculate the input susceptance of a disk-loaded rectangular waveguide. Satisfactory agreement with experimental results is obtained.     

Electromagnetic field of a rectangular patch of uniform and lineardistributions of current

Closed-form expressions for a class of indefinite double integrals are presented. Using these formulas, exact analytical expressions for the magnetic vector potential and the electric and magnetic fields of a rectangular patch of uniform and linear distributions of electric current in an unbounded homogeneous medium are derived. The field expressions obtained are valid everywhere, in particular in the source region. Computed results verifying the correctness and accuracy of these expressions are presented     

Characteristic modes of a rectangular aperture in a perfectlyconducting plane

The objective of the paper is the analysis of a rectangular aperture in a perfectly conducting plane using the characteristic mode theory. The problem is first formulated as an operator equation involving the continuity of the tangential components of the magnetic field in the aperture region. The operator equation is used, with the help of the moment method, to determine the eigenvalues, eigencurrents, and the characteristic magnetic currents of the aperture. When these modes are determined, the equivalent magnetic current and other parameters of interest can then be obtained     

Effect of a finite ground plane on radiated emissions from acircular loop antenna

A thin-wire circular loop antenna located above a perfectly conducting square plate is analyzed by a physical optics (PO) method. The electric field integral equation (EFIE) is solved using the method of moments to compute the current on the loop in the presence of an infinite ground plane whereby the edge effects of the plate on the loop current are neglected. The current distribution on the loop is obtained from a full-wave Fourier series analysis which requires no matrix inversion. We then use physical optics to compute the current induced on the plate in terms of the incident magnetic-field intensity. Our aim is to compare the PO solution with results obtained from a mixed wire-patch MOM code and explore its accuracy as a function of plate size and loop height. The benefits are considerable reduction in analytical and computational efforts and much less CPU time     

Magnetic moment and surface dipole distributions of circular holesin a conducting screen

This paper presents a method to account for the quasi-static magnetic interaction among circular holes in a conducting screen. Employing the oblate spheroidal system of coordinates, we derive expressions for the field arising when magnetic point charges and dipoles of arbitrary orientation are brought close to the hole in the plane of the screen. Using a set of two-dimensional (2-D) integrals for the Legendre polynomials, the “modes” for the potential are interpreted as being due to certain eigenfunctions expressing the density distribution of superficial magnetic dipoles in the plane of the hole. The dipole distributions are applied in discretised form to estimate the coupling of the surface polarizations of two similar circular holes     

The variational method and the method of moments in the problem of plane wave scattering by a rectangular cavity in an impedance screen

The problem of electromagnetic plane wave diffraction by a rectangular cavity in an impedance screen is solved. The problem is reduced to solution of a Fredholm integral equation for the field function in the aperture. The equation has a symmetric kernel. Expressions for the angular distribution of the scattered far-field are obtained by the method of moments and the variational method. Numerical results are analyzed and compared.