Fields from point sources using the aperture field method

It is shown that the field of arbitrary point sources can be found from the aperture field method. It is demonstrated that the exact result in the far field is easily obtained for an electric Hertzian dipole in free space     

Forward scattering from square cylinders in the resonance region with application to aperture blockage

The relationship between the induced field ratio (IFR) of a cylinder and aperture blocking of a constant-phase aperture by cylindrical struts is discussed. An analytical technique is presented whereby the IFR of rectangular cylinders can be calculated using the method-of-moments with internal constraint points. An experimental technique using a forward-scattering range is used to measure the IFR's of square and circular cylinders in an anechoic chamber. These experimental results are compared with the theory, and their implications on aperture blocking losses and boresight cross polarization are discussed.     

Support scattering effects on low-gain satellite antenna pattern measurements

The purpose of the present investigation is to determine the difference between the scattering effects from two types of supports on satellite antenna pattern measurements. The difference in scattering effects is estimated by comparing low-gain antenna patterns recorded when using a foam tower and a model tower.     

Echo width of foam supports used in scattering measurements

Theoretically and experimentally determined echo widths of dielectric cylinders having circular, triangular, and quadratic cross sections have been compared. The cylinders were made of foam material having a relative dielectric constant of about 1.035. The purpose of the investigation was to find a cross section with a small echo width. The result can be used in selecting a proper support for test objects in backscattering measurement studies.     

EM programmer's notebook

This article covers two contributions. One contribution is by Dr. Peter Petropoulos, who gives recommendations for the sampling density in finite-difference time-domain simulations. His observations point out that higher-order elements may be essential for large-scale implementations. He also provides a rigorous proof. The second contribution is by Dr. J. Appel-Hansen, who presents a non-trivial problem, but one amenable to a trivial solution. The problem involves two arbitrary but identical, properly placed sources, illuminating a flat plate of an arbitrary shape. Consequently, it can be used to possibly validate scattering and antenna codes     

A Van Atta reflector consisting of half-wave dipoles

The reradiation pattern of a passive Van Atta reflector consisting of half-wave dipoles is investigated. The character of the reradiation pattern first is deduced by qualitative and physical considerations. Various types of array elements are considered and several geometrical configurations of these elements are outlined. Following this, an analysis is made of the reradiation pattern of a linear Van Atta array consisting of four equispaced half-wave dipoles. The general form of the reradiation pattern is studied analytically. The influence of scattering and coupling is determined and the dependence of the reradiation pattern on the length of the transmission lines interconnecting the dipoles is investigated. The optimum length of the transmission lines is determined. The results, found by the analysis of the reradiation pattern, are verified experimentally. The experimental reflector consists of slot-fed dipoles with open-ended terminations. Line stretchers are inserted into the transmission lines.     

Experimental study of surface-wave propagation on a low-permittivity medium

It is experimentally shown that a surface wave having d?2 dependence can propagate on a medium having a dielectric constant near unity, when excited by a low-gain source near the interface. This occurs for both parallel and perpendicular polarisation.     

Comments on field equivalence principles

It is pointed Out that often-used arguments based on a short-circuit concept in presentations of field equivalence principles are not correct. An alternative presentation based on the uniqueness theorem is given. It does not contradict the results obtained by using the short-circuit concept but provides further insight.     

Matching of equivalent field regions

In aperture problems, integral equations for equivalent currents are often found by enforcing matching of equivalent fields. The enforcement is made in the aperture surface region adjoining the two volumes on each side of the aperture. In the case of an aperture in a planar perfectly conducting screen, having the same homogeneous medium on both sides and an impressed current on one side, an alternative procedure is relevant. We make use of the fact that in the aperture the tangential component of the magnetic field due to the induced currents in the screen is zero. The use of such a procedure shows that equivalent currents can be found by a consideration of only one of the two volumes into which the aperture plane divides the space. Furthermore, from a consideration of an automatic matching at the aperture, additional information about tangential as well as normal field components is obtained. We compare the two procedures in this tutorial article.