Random phase and time of arrival statistics for circular disk scattering model

Wireless Networks - Fading simulators are tested by verifying the statistics of channel created by multipath environment. These statistics are an angle of arrival (AoA), time of arrival (ToA), and...     

Higher order diffractions from a circular disk

The backscattering from a circular disk is analyzed using the geometrical theory of diffraction (GTD). First-, second-, and third-order diffractions are included in the hard polarization analysis, while first-, second-, and second-order slope diffractions are included for soft polarization. Improvements in the prediction of the monostatic radar cross section (RCS) over previous works are noted. For hard polarization, an excellent agreement is exhibited between experimental and theoretical results, while a very good agreement is noted for soft polarization. To further improve the soft polarization results for wide angles, a model for the creeping wave or circulating current on the edge of the disk is obtained and used to find an additional component of the backscattered field. The addition of this component significantly improves the results for wide angles, leading to excellent agreement for soft polarization also. An axial-caustic correction method using equivalent currents is also included in the analysis.     

Numerical analysis of circular disk microstrip antennas with parasitic elements

Efficient numerical analysis of double tuned circular disk resonators/radiators is described. This method is based upon the Hankel transform domain analysis. Several numerical examples of input voltage standing-wave ratio (VSWR) characteristics and radiation patterns are compared with available experimental data.     

Monopole antenna on circular disk

The sinusoidal-Galerkin moment method is developed for the impedance of a monopole antenna at the center of a circular disk in free space. Numerical results are presented for the impedance and current distributions as a function of the disk radius.     

Electromagnetic scattering from a dielectric-coated circular cylinder

The normalized backscattering width of an infinitely long, dielectric coated circular cylinder is obtained via a high frequency ray solution. The ray solution provides a physical picture of the scattering process in terms of a geometrical optics ray and two surface waves. It is shown that the surface wave resonance phenomena in the backscattering fields of the coated cylinder can be predicted in terms of the Regge poles of the coated cylinder. The numerical results for the backscattering widths of the cylinder obtained via the high frequency ray solution show excellent agreement with the eigenfunction results. The trajectories of the Regge poles associated with the coated circular cylinder are also presented.     

Transient scattering from a thin arbitrary wire

The conjugate gradient method is applied to solve the problem of transient scattering from a thin arbitrary wire. The method is simple, efficient, and yields more accurate results than the marching-on-in-time procedure. Numerical examples for the case of a bent wire, a wire with discontinuous radii, and a circular loop are presented to highlight the advantages of this procedure. It is concluded that the occurrence of late-time oscillations may not be due to the accumulation of truncation of roundoff errors. These oscillations may be attributed to the insufficient sampling of the structure.<>     

Transient radiation field of a circular loop antenna

For a circular loop antenna excited by a frequency-hand-limited rectangular voltage pulse, the time variation of the electric field at remote points in various directions has been computed. The computations are for a loop of radiusbmade from wire of radiusa, for which the thickness parameterOmega = 2 ln (2pi b/a) = 15. The moment method was used in obtaining the current distribution on the loop due to each harmonic component in the excitation. Then the transient field is obtained by using the harmonic current distribution due to each frequency component of the exciting voltage pulse.     

Transient response of a dipole over a circular ground screen

The time-domain response of a vertical electric dipole located over a circular ground screen is considered. The relevant time-harmonic solution is used as a starting point. By making a number of approximations a very simple formula is obtained for the transient response of the far field when the dipole current moment is a ramp function of time. It is shown that for early times, the pattern response appears as if the ground screen were of infinite extent, while at very long times, the response approaches that expected for a homogeneous flat ground.     

Switchable circular disk antenna for RCS and mobile communications applications

In this paper, we describe the operation of a low profile, 3 mm deep, circular disk antenna which requires a small ground plane, and incorporates a shorting bar which can be rotated. The position of the shorting bar determines the return loss and radiation characteristics of the antenna element. In one mode at 2.34 GHz the antenna exhibits a return loss of better than -25 dB, 5 dBi gain, and a conical/monopole beam pattern suitable for radar tracking/mobile communications applications. When the short circuit is positioned at 90 degrees the return loss at 3.52 GHz becomes -18 dB, 7 dBi gain, and the antenna exhibits normal linear polarized broadside cosine radiation characteristics. In addition when the short circuit is positioned at zero degrees at 3.52 GHz the antenna gives -1 dB return loss and by reciprocity will act as a reflector to incoming energy. Theoretical results are provided in support of the experimental results observed and are used to explain the operating mechanisms of the antenna.     

Analysis of a circular microstrip disk antenna with a thick dielectric substrate

The problem of a circular microstrip disk excited by a probe is solved using rigorous analysis. The disk is assumed to have zero thickness, and the current on the probe is taken to be uniform. Using vector Hankel transforms the problem is formulated in terms of vector dual-integral equations, from which the unknown current can be solved for. Due to the singular nature of the current distribution arising from probe excitation, the direct application of Galerkin's basis function expansion method gives a slowly convergent result. Therefore the singular part of the current is removed since the singularity is known a priori. The unknown current to be solved for is then regular and tenable to Galerkin's method of analysis. It is shown that this analysis agrees with the single-mode approximation when the dielectric substrate layer is thin, and that it deviates from the single-mode approximation when the substrate layer is thick. Excellent agreement of both the computed real and imaginary parts of the input impedance with experimental data is noted. The radiation patterns and the current distributions on the disk are also-presented.     

UTD solution for electromagnetic scattering by a circular cylinderwith thin lossy coatings

A uniform geometrical theory of diffraction (UTD) solution is obtained for the field exterior to a two-dimensional circular cylinder with a thin lossy dielectric coating. The solution is convenient for engineering applications due to its simple ray format. In the lit region, the geometrical optics (GO) solution consists of the direct incident ray and the reflected ray. In the shadow region, the geometrical theory of diffraction (GTD) uses the creeping-wave format to calculate the diffracted field. In the transition regions adjacent to the shadow boundaries, where the pure ray optical solution fails, a `universal' transition integral is used for the UTD solution to calculate the field. Numerical values for the essential transition integral are deduced, by a heuristic approach, from alternative representations of the Green's function for a circular cylinder with coating. Numerical results obtained from the UTD solution show excellent agreement with the eigenfunction results for cylinders with thin dielectric coatings     

TM scattering from a hollow slotted circular cylinder withthickness

TM scattering from a hollow, slotted, circular cylinder with thickness is investigated. The mode-matching technique (MMT) is used to express the scattered and guided fields in the angular spectral domain in terms of the radial waveguide mode. The boundary conditions are enforced on the conducting surface and the slot to obtain simultaneous equations. The simultaneous equations are solved to represent the fields in an analytic series form. The computed results are in very good agreement with other data. The numerical computations are performed to illustrate scattering behavior in terms of cylindrical geometry, incident angle, and frequency     

Scattering from a circular disk: a comparative study of PTD and GTDtechniques

Two groups of techniques, PTD (physical theory of diffraction) and GTD (geometric theory of diffraction), are studied by analyzing the scattering from a conducting circular disk. The authors include comparisons of calculations based on several different asymptotic high-frequency theories with the method of moments (MoM) as a baseline. The latter is treated as numerically exact. Features of particular interest include the performance at the reflection boundaries, boresight caustics, and far-angle sidelobes. The bistatic radar cross sections (RCSs) calculated by these techniques are examined. Although only far-field radiation is considered, these methods can also be used for near-field calculations     

Transient scattering by resistive cylinders

The two-dimensional scattering of an electromagnetic pulse normally incident on a collection of infinitely long cylinders of arbitrary shape is considered. ForE-polarization an electric field integral equation is derived that is applicable to solid cylinders and/or thin sheets, resistive and/or perfectly conducting. The contribution of the self-cell at later times is carefully analyzed. The expression obtained represents a generalization of previously known results. For an incident Gaussian pulse, numerical results are presented for surface currents and far-fields, for perfectly conducting and resistive circular cylinders and strips. A fast Fourier transform (FFT) algorithm is implemented to obtain the backscattering radar cross section, which is in good agreement with results obtained from either exact continuous wave (CW) solutions or the method of moments.     

Transient scattering from conducting cylinders

A method for determining the fields scattered by arbitrarily shaped cylindrical conducting structures with a transient incident wave is described. The transient scattering problem is reduced to the solution of a time domain integral equation which in turn is solved directly in the time domain by means of a digital computer. The approximate electromagnetic impulse response for a number of cylindrical scatterers is calculated using this method.     

Accuracy analysis and optimization of the method of auxiliary sources (MAS) for scattering by a circular cylinder

This paper presents a rigorous accuracy analysis of the method of auxiliary sources (MAS), when applied to scattering problems. A benchmark, canonical geometry, consisting of a perfectly conducting, infinite, circular cylinder, is chosen for clarity and simplicity. For this particular structure it is shown that the MAS square matrix can be inverted analytically, yielding exact mathematical expressions for the discretization error and the condition number of the pertinent linear system. It is also demonstrated that the error increases very abruptly for source locations associated with the characteristic eigenvalues of the scattering geometry, precisely as predicted in theory. Various plots depict comparisons between analytical and computational data for the boundary condition error, and all occurring discrepancies are fully explained. Among several important results of the analysis, the fundamental MAS question concerning the optimal location of the auxiliary sources is thoroughly investigated and resolved on the grounds of error minimization.     

Low-profile circular disk DR antenna of very high permittivityexcited by a microstripline

A microstripline-fed dielectric resonator (DR) antenna disk of very high permittivity is investigated experimentally. The configuration has the advantage of being low-profile and allows the ground plane to be arbitrarily thick for mechanical support and/or heatsink purposes. The return loss, radiation patterns, and antenna gain of the configuration are studied and compared with those of the aperture-coupled version     

Monopole antenna on circular disk over flat earth

The sinusoidal-Galerkin moment method is developed for a vertical monopole antenna at the center of a circular disk over the flat earth. Numerical results are included for antenna impedance and current distribution.     

Spectral and transient response of a circular disk to plane electromagnetic waves

Extensive theoretical far-field amplitude and phase data are presented for the monostatic scattering of an electromagnetic plane wave normally incident upon a thin circular metallic disk. These data are used to synthesize the impulse response of the disk. Comparisons are made with various approximate techniques in both the frequency and time domains.     

Transient analysis for a new CMOS latchup model

In this paper, a new lumped element latchup model which includes two extra bipolar transistors is proposed. The divergence between the results of the conventional and the proposed model is explained in terms of the circuit parameters. An analytical model for the latchup triggered by the voltage transient at the power supply is presented and the predictions of the model are computed and compared to the analytical results of the conventional model and the simulation results using SPICE.