Near-Field and Plane-Wave Electromagnetic Coupling into a Slotted Circular Cylinder: Hard or TE Polarization

An analytically tractable model is proposed in this initial study of the electromagnetic phenomena that control our ability to synthesize, by using a near-field source, the effect of plane-wave coupling through an aperture into the interior of a vehicle under test. An integral equation for the tangential electric field in the slot aperture of a perfectly conducting, infinitesimally thin-walled circular cylinder is solved using a basis set of Chebyshev polynomials that are properly weighted according to the static edge condition. The resulting matrix elements from a Galerkin procedure are computed to high precision upon extracting the logarithmic singularity of the kernel of the integral operator. Exact expressions for the matrix elements, in the form of rapidly convergent series of elementary terms, are constructed by isolating another logarithmic function of the aperture width. A minimization of the mean-square error between the true plane-wave response and that due to a near-field line-source establishes the optimal complex source strength of the near-field source     

A modal radar cross section of thin-wire targets via thesingularity expansion method

A modal radar cross section (RCS) of arbitrary wire scatterers is constructed in terms of singularity expansion method parameters. Numerical results are presented for both straight and L-shaped wire targets and are compared to computations performed in the frequency domain using the method of moments     

Capacitance bounds and equivalent radius

The isolated capacitance of conducting ellipsoids is calculated, and the resulting values are presented in the form of equivalent radii. These data are used to establish bounds for the capacitance of other conducting objects, namely, the right circular cylinder and the rectangular parallelopiped.     

Penetration through slots in conducting cylinders. Part 2: TM case

For pt.1 see ibid. vol.46, no.11, p. 1611-20. Three methods for determining the penetration through small apertures in closed conducting surfaces are outlined and their salient features discussed. These methods are designated: (1) the scatterer method; (2) the short-circuit current method; and (3) the equivalent current method. They are implemented by integral equation techniques but are amenable to differential equation or hybrid methods. Procedures for applying each method are outlined as are schemes for repairing singular equations rendered invalid by the presence of false resonances. Reasons for inaccuracies in the three methods are also delineated. Data determined for a given structure by all three methods are presented and numerical examples that illustrate important features of the methods and their relative accuracies are described. An outline is given of the integral equation formulation and numerical scheme needed to accurately determine the field that penetrates through a slot in a conducting cylinder, excited by an axially independent TM source     

Backscatter RCS for TE and TM excitations of dielectric-filledcavity-backed apertures in two-dimensional bodies

Transverse electric (TE) and transverse magnetic (TM) scattering from dielectric-filled, cavity-backed apertures in two-dimensional bodies are treated using the method of moments technique to solve a set of combined-field integral equations for the equivalent induced electric and magnetic currents on the exterior of the scattering body and on the associated aperture. Results are presented for the backscatter radar cross section (RCS) versus the electrical size of the scatterer for two different dielectric-filled cavity-backed geometries. The first geometry is a circular cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the cylinder is dielectric filled and is also of circular cross section. The two cylinders (external and internal) are of different radii and their respective longitudinal axes are parallel but not collocated. The second is a square cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the square cylinder is dielectric-filled and is also of square cross section     

Intermodulation effects induced on parallel wires by transientexcitation

The analysis of the transient response of a five-wire planar array of identical thin wire scatterers is presented. The transient current induced on the individual wires comprising the array exhibits inherent intermodulation effects. This particular effect is explained in terms of the excitation of several of the natural frequencies obtained by applying the singularity expansion method (SEM) to the multiple-wire arrays. The natural frequencies group themselves into layers that can each be associated with the natural singularities of the isolated thin-wire scatterers, that constitute the individual elements in the array. Calculation of the coupling coefficients associated with the natural modes corresponding to the natural frequencies illustrates the manner in which different intermodulation frequencies appear in the transient response of the array as a function of the excitation orientation and polarization. Tables and curves illustrating the pertinent parameters determining these intermodulation effects are presented for one-, two-, three-, four-, and five-wire arrays     

Parallel-plate mode reduction in conductor-backed slots usingelectromagnetic bandgap substrates

By fabricating a resonant slot over a reflecting back plate and filling the resulting parallel-plate with an appropriately designed artificial electromagnetic bandgap (EBG) structure, noticeable enhancements in both radiation pattern and bandwidth are achieved using a significantly lower profile than traditional designs. This design uses a two-dimensional artificial EBG substrate in conjunction with a reflecting plate to completely block radiation from the backside of the slot from propagating to the finite edges of the resulting parallel-plate cavity. Measured and simulated data for conductor-backed slots with homogeneous substrates and with EBG substrates are compared     

A new surface impedance function for the aperture surface of aconducting body with a dielectric-filled cavity

A surface impedance function (SIF) appropriate for use on the aperture surface of a conducting body with a dielectric-filled cavity, is presented. Unlike the usual SIFs that might be used on an aperture, this SIF takes into account not only the wave transmitted through the aperture but also the wave reflected from the inside of the cavity the shape of the aperture and cavity, and the polarization and direction of the incident wave. The SIF is derived heuristically from the series-reflection solution for a plane wave normally incident on an infinite flat conducting plate with a flat dielectric coating. The SIF was developed and used in a combined method of moments solution for the scattered fields due to an incident plane wave. This combined technique greatly reduces the number of current expansion coefficients to be determined using the method of moments and hence also reduces the number of impedance elements required for calculation in the method of moments. Application of the SIF in a combined method is illustrated for a two-dimensional object     

Singularity expansion method analysis of regular polygonal loops

The singularity expansion method parameters (natural frequencies, natural modes, and coupling coefficients) for regular planar polygonal loops (equilateral triangle, square, regular pentagon, and regular hexagon) are computed and compared to those determined for the regular 60-gon (pseudo-circular) loop. Common characteristics of these geometries are compared and contrasted with respect to their use as radiating antenna structures or scatterers. The approach results in new insights for these canonical loop structures     

Electromagnetic pulse generation by an impedance loaded dipole antenna

A theoretical study is made for obtaining the pulse radiated from an impedance loaded dipole. Numerical results are presented for an antenna that is slowly charged and suddenly shorted at the terminals. The impedance loadings are chosen as those on an existing antenna located at Sandia Laboratory, Albuquerque, N. Mex.