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.
Synthesis of a circular polarized field radiated by an electric dipole located over a rectangular screen
A radiating system consisting of a rectangular perfectly conducting screen and an oblique electric dipole is considered. An algorithm taking into account diffraction by the edges of the screen is developed for determination of the dipole’s slope angle such that the radiated field is circularly polarized in the principal observation planes. The effect of the dipole position relative to the screen on the polarization properties and gain of the system radiating a circularly polarized field is investigated. It is shown that these characteristics exhibited in a given direction can be optimized through selection of the dipole’s position and slope angle.
New records of Grania (Clitellata, Enchytraeidae) in the Northeast Atlantic (from Tromsø to the Canary Islands), with descriptions of seven new species
Previous northeast Atlantic records of Grania have been mainly from Germany, southern Scandinavia, and the Atlantic shores of France, Spain and Ireland. They were referred to eight species, with one, G. atlantica, reported from the continental slope. We have examined various unpublished collections from sources spanning from the Canary Islands to the Norwegian Arctic. Apart from new information on morphology, taxonomy, and distribution of known species, we describe seven new taxa (G. canaria, G. fortunata, G. mauretanica, G. aquitana, G. vikinga, G. torosa, and G. papillinasus). The collection of G. papillinasus from 2630-2885 m represents a new depth record for Enchytraeidae. Twenty-five of the now 57 Grania species occur in the North Atlantic. The North Atlantic drift moderates sea temperatures along the northeast Atlantic coasts, probably facilitating the wide latitudinal range of some taxa, as well as actual dispersal within the region. A "chaetal index" (chaetal length : chaetal foot length) is proposed to differentiate L-shaped chaetae at the species level. Complex relationships within the "type 6 group" of Grania suggest that groupings established using certain combinations of penial, chaetal and spermathecal patterns may not be monophyletic. For a better phylogenetic resolution, additional morphological details of these and other characters are needed.