Parabolic reflector

About: Parabolic reflector is a research topic. Over the lifetime, 3375 publications have been published within this topic receiving 30735 citations. The topic is also known as: paraboloid reflector & paraboloidal reflector.

Geometric modeling and analysis of large latticed surfaces

Abstract: The application of geometrical schemes, similar to geodesic domes, to large spherical antenna reflectors was investigated. The shape and size of flat segmented latticed surfaces which approximate general shells of revolution, and in particular spherical and paraboloidal reflective surfaces, were determined. The extensive mathematical and computational geometric analyses of the reflector resulted in the development of a general purpose computer program capable of generating the complete design parameters of the dish. The program also includes a graphical self contained subroutine for graphic display of the required design.

Simulation of a metallic SNOM tip illuminated by a parabolic mirror

Abstract: We investigate numerically a Scanning Near field Optical Microscope (SNOM) that uses a Parabolic Mirror (PM) to focus a radially polarized beam on a metallic tip. In order to overcome problems - like overestimated near fields or resonances - that arise when only considering finite tips, we have introduced a semi-infinite continuation of the tip, which incorporates the analytic solution of surface waves. For a realistic modeling the right description of the incident field is essential and we have complied with this requirement by a Bessel expansion of the focal fields, which is also applicable to an aplanatic objective. The established numerical model is used for an extensive study of model parameters like tip geometry, illumination directions and tip materials (Ag, Au, Al and Cu). Compared with a simplified inverted microscope configuration, the PM setup shows an increased field enhancement (factor of 2–2.5), which can be ascribed to the efficient coupling of the exciting field to tip surface plasmons.

Improvements in aerials

Abstract: 741,911. Aerials. BELLING & LEE, Ltd. Oct. 25, 1954 [Oct. 23, 1953], No. 29357/53. Class 40 (7). An aerial assembly comprising two aerials which are mechanically inter-related for mounting on a single support, the aerials being capable of receiving signals in different frequency bands and having only a small effect on each other, includes a halfwave dipole for operation at the lower frequency and a plurality of closely spaced conductors forming a reflective surface which is part of the higher frequency aerial. Each conductor is arranged to lie wholly in a plane perpendicular to the half-wave dipole. In a first embodiment a half-wave dipole 1 backed by a parasitic reflector 2 is provided for operation at the lower frequency and the conductors 6 forming the reflective surface are supported by but insulated from the upper parts of the elements 1 and 2. A stouter conductor 7 forms the support bar for a broadside array 5 of elements working at the higher frequency. These elements are spaced a quarter of a wavelength in front of reflective surface by members 8. Where the half-wave dipole 1 is specially mounted in a rotatable coupling 10 and the conductive rods 6 supported through insulators at their centres the whole higher frequency aerial may be rotated for directional adjustment. The ends of the conductors 6 are held in vertical insulating supports 11 and the reflecting surface may be a plane one (Fig. 2, not shown) or parabolic as in Fig. 3. The array of elements 5 may be stacked vertically so as to lie along the focal line of the parabolic reflector. In Fig. 4 the lower frequency dipole 1 is horizontal and the conductors 6 are insulated and mounted so as to extend horizontally in a vertical plane, an array of higher frequency elements 5 being arranged as described with reference to Fig. 1. The top and bottom of the reflecting surface may extend forward so that a parabolic reflector with a horizontal focal line is formed (Fig. 5, not shown). In a modification of the Fig. 4 embodiment the conductors 6 and elements 5 may be arranged to extend vertically and in this case the reflector surface need not be a plane perpendicular to the dipole 1 but may make an angle other than 90 degrees with it in the horizontal direction. In the modification, too, the reflector may be parabolic.

The Large Adaptive reflector : A 200-m diameter, wideband, cm-m wave radio telescope

Abstract: The Large Adaptive Reflector (LAR) is a concept for a low-cost, large aperture, wideband, radio telescope, designed to operate over the wavelength range from 2 m to 1.4 cm. It consists of a 200-m diameter actuated-surface parabolic reflector with a focal length of 500 m, mounted flat on the ground. The feed is held in place by a tension-structure, consisting of three or more tethers tensioned by the lift of a large, helium-filled aerostat-a stiff structure that effectively resists wind forces. The telescope is steered by simultaneously changing the lengths of the tethers with winches (thus the position of the feed) and by modifying the shape of the reflector. At all times the reflector configuration is that of an offset parabolic antenna, with the capability to point anywhere in the sky above -15° Elevation Angle. At mid-range wavelengths, the feed is a multi-beam prime-focus phased array, about 5 m diameter; at meter wavelengths, it is a single-beam phased array of up to 10 m diameter. Simulations have shown that in operating wind conditions (10 m / s average speed with 2.5 m / s gusts), the position of the feed platform can be stabilized to within a few cm over time scales of -20 s. Research indicates that the telescope concept is feasible and that an order of magnitude improvement in cost per m 2 of collecting area over traditional designs of large parabolic antennas can be achieved.