C. Ryan

Near-field scattering measurements for determining complex target RCS

The application of near-field scattering measurements for determining the near-zone and far-zone radar cross section (RCS) of complex targets that are both physically and electrically large is reviewed and examined in the light of recent advances in near-field measurement technology and data processing capabilities. >

Plane wave spectrum scattering analysis of near-field obstacle effects on directive antenna patterns

A plane wave spectrum scattering analysis of the effects of a near-zone obstacle on the pattern performance of a directive antenna is discussed. The free-space azimuth monopulse antenna is characterized by its sum and difference mode plane wave spectra, and a computed plane wave scattering dyad is used to characterize the scattering by a metallic right circular cylinder when it is excited by the incident antenna spectra. An efficient computer algorithm has been developed to compute the far-zone scattered and total fields for the antenna/cylinder system. Extensive experimental data have been obtained, and the patterns calculated using the present analysis are in agreement with the measured data.

Analysis of antennas on finite circular cylinders with conical or disk end caps

The techniques of wedge diffraction and edge currents are applied to compute the radiation patterns of radial monopole and circumferential slot antennas on a finite circular cylinder having conical or disk end caps.

Open mast scattering investigation

The Georgia Tech automated planar scanner has been employed to measure the forward scattered plane wave spectrum (PWS) for both a circular cylinder mast and a tripod open mast. The experimentally derived spectra have been used in a plane wave spectrum scattering analysis to compute the main beam gain-loss and pattern effects of the circular cylinder and tripod masts for a paraboloidal antenna. This investigation demonstrates the practical use of a planar scanner to obtain forward scattering patterns for complex scatterers.

Scattering by arbitrary-shaped over-moded waveguides

The first six TE modes were used to compute the RCS (radar cross section) for a shorted trapezoidal waveguide. It was found that the individual-mode RCS patterns did not agree with measured RCS patterns, and it was necessary to use a combination of modes to obtain satisfactory results. The calculated domain single-mode azimuth-plane RCS and measured RCS were compared. This single-mode calculation underestimates the measured RCS. The measured RCS data, taken over a frequency range of 2 to 18 GHz and an angular range of +/-70 degrees , exhibit fluctuations that indicate phase interference between multiple waveguide modes. Since the precise relative phase between the higher order modes are not usually known, a statistical approach was used to compute a mean RCS and standard deviation. A comparison between the statistically calculated RCS and the fluctuating measured data between 6.75 and 6.95 GHz is shown.<<ETX>>

PWS Scattering computation

Recently, due to the ability of a computer to perform two-dimensional (2D) Fourier transformations via the Fast Fourier Transformation (FFT) algorithm and its capability to perform numerical integrations, Plane Wave Spectrum (PWS) Scattering techniques have become practical. The PWS scattering analysis represents a radiating source by a twodimensional spectrum of plane waves and characterizes a scatterer by its PWS scattering matrix. The scattered field is then obtained by calculating the integral of the inner product of the incident PWS and the scattering matrix. This calculation is, in effect, a 2D integration performed over the set of incident plane waves. It is the objective of this article to demonstrate that this analysis is, in fact, simple and straightforward. Several examples will be presented wherein simple scattering models, such as Physical Optics, have been used to describe the PWS scattering matrix and thus calculate the scattered field with good results. Also, the technique is both straightforward and powerful for the analysis of antenna coupling in the presence of obstacles. These examples demonstrate that the PWS Scattering Matrix method is a practical and cost effective approach to the analysis of many near-field scattering problems.

Electromagnetic Models for Antenna Performance, EMC, and Biological Effects

This paper describes several models which have been developed at Georgia Tech for the analysis of antennas, EMC, and biological effects. These models include algorithms based upon the plane-wave-spectrum scattering-matrix analysis, the geometrical theory of diffraction, and the method of moments. In addition, statistical models for antenna coupling, for out-of-band antenna performance, and for scattering by complex structures are discussed. In each case, the model results are compared with measured data to assess the accuracy of the modeling technique.