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Antenna array Complex directional antenna consists of separate near-omnidirectional antennas (radiating elements) positioned in the space and driven by high-frequency … (from 'Glossary' of our web–site)  |
All Archives11/ 12/ 13/ 14/ 15/ all pages Sunday, December 18, 2005 at 12:12AM
The problem of diffraction of electromagnetic waves on a curvilinear surfaces with piecewise continuous admittance (impedance) boundary conditions, particularly on open-ended metallic surfaces is considered. It is shown that the coefficients of Fourier kind for some complete function system and the corresponding series for the function equal to the tangent component of the electric vector on the part of the surface where the admittance is finite and the surface electric current on the part where it is infinite, can be found by solving the inner and exterior boundary value problem. Each of the terms of the series satisfies the Meixner condition and the determined values of the tangent field on the given surface allow determining of the scattered field in the whole space. The method is illustrated with a sample of diffraction of a plane wave on a circular cylinder with the admittance periodically alternating in steps along the axis.
Saturday, December 17, 2005 at 12:12AM
The article expresses the conditions that must be met when measuring the radio-locating cross-section of a target in terms of amplitude and incident field phase variation. A number of minimal distance criteria are examined. The analysis of minimal distance for the cases when the antenna has a uniformly lighted square aperture is given, and the relation that binds the minimal distance to the sensitivity of measurements. The measurements of the reflection properties of small targets in near zones of focused and unfocused apertures are described. It is shown that the “minimal distance” can be substantially lowered using the suitable microwave lens when measuring the reflection properties of medium and large-sized targets.
Friday, December 16, 2005 at 12:12AM
Researche and optimization of characteristics of lens antennas based on a homogenous dielectric sphere, taking into account the aberration effects, reflections, dielectric losses, radiator directional diagrams, matching layers and technological tolerance are carried out; the relation of antenna characteristics to its geometrical dimensions and dielectric parameters is derived; the maximum possible antenna characteristics are determined; the characteristics of antennas based on a homogenous sphere and Luneberg lens are compared; the estimation of hydrometeor (water, ice) effect on antenna characteristics is given.
Thursday, December 15, 2005 at 12:12AM
The method for calculating the electromagnetic field of a radiating object in its near zone, the derived singular integral representations for the components of the electromagnetic field allow for computing the field in any point of space by integrating the direct-axis current is offered; the standard method uses the thin vibration generator method that leads to the Poklington or Hallen integral equations (Fredholm equation of 1st kind)
Wednesday, December 14, 2005 at 12:12AM
The method of determining the antenna directional diagram using the amplitude and phase measurements in the Fresnel zone is considered; the mathematical rationale of the method is given along with the results of computer and experimental modeling and the samples of using when measuring the high aperture antennas in an anechoic room with a 80 m route on a measurement stand in a far zone.
11/ 12/ 13/ 14/ 15/ all pages |
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