Formation of circularly polarized wave by impedance wire dipole located over square screen
For a radiating system consisting of a resonant half-wave impedance oblique wire dipole and a rectangular perfectly conducting screen the conditions guaranteeing formation of a circularly polarized wave with extremely achievable field amplitude in the set directions of the main observation planes are investigated. Computation of the far field components is based on the asymptotic solution of 3D vector problem of diffraction of the field of electric dipole on the ideally conducting rectangular screen, obtained by the method of uniform geometric diffraction theory. To define a wire dipole's slope angle guaranteeing equality of the amplitudes of the orthogonal field components, the technique with account of diffraction effects on edges of the finite size screen is developed. It is shown that in defined interval of the observation angles the circularly polarized wave with extremely achievable field amplitude may be formed by a choice of appropriate wire dipole's slope angle and removal from a screen.
Resonant phenomena at diffraction of tilted impedance dipole field on finite size screen
The 3D radiation patterns of the tilted impedance wire dipole located over a perfectly conducting infinitely thin finite size screen are investigated by the uniform geometric diffraction theory method. The technique is developed for definition of a slope angle of the wire dipole taking into account the diffraction effects on the screen edges at which the circularly polarized wave in the set directions of the main observation planes in the far zone is radiated. The extremely achievable field amplitude of the circularly polarized wave in the certain angles of the main observation planes as well as the appropriate dipole's slope angles depending on the square screen sizes are defined. It is shown that the resonant phenomena take place on account of diffraction effects on screen edges. At certain dipole's spacing the radiation intensity in case of exiting screen by a resonant impedance dipole more than twice exceeds intensity in case of exiting screen by ideally conducting dipole with the same length.
Routine quantitative phase analysis of niobium-bearing lateritic ores
Routine quantitative analyses by Rietveld full-pattern fitting have been carried out on more than one thousand niobium ore samples originating from four pyrochlore deposits: Lueshe and Bingo (D.R. Congo), Mabounie (Gabon), and Sokli (Finland). The ore samples were characterized by a highly variable mineral content, the presence of mineral phases with a wide range of compositions and a high amorphous content. An analytical procedure was established which addressed several problems: creation of an appropriate crystallographic parameter database, specimen preparation, check for preferred orientation and measurement of the amorphous content by the internal standard method.