Reflector (antenna)

About: Reflector (antenna) is a research topic. Over the lifetime, 28730 publications have been published within this topic receiving 212618 citations.

Method and apparatus for automatic acquisition and alignment of an optical beam communication link

Abstract: A method and a preferred apparatus for the searching, acquisition and locking into boresight alignment of two remote optical beam transceivers suitable for use in satellite communications. A first transceiver operates in a search mode while acquiring a communications link with a second transceiver operating in a stare mode. Each transceiver has an optical axis and a retro-reflector that reflects incident beams that are not substantially aligned with the local optical axis while not reflecting all incident beams substantially aligned with the local optical axis. Each transceiver includes an axis-aligned beam transmitting source, a axis-aligned optical detector for incoming beams, a pointing system for aiming the local optical axis in any direction over a hemispherical range, and a beam tracker for maintaining boresight alignment following acquisition. The decision processor includes means for distinguishing between optical beams reflected from the second transceiver and optical beams transmitted by the second transceiver. In operation, the reflected beam increases in intensity as the two transceivers approach alignment but drops to zero as the transceivers attain boreslight alignment. The preferred apparatus includes a matched pair of reflecting telescopes rigidly mounted on a gimballed platform with the transmitting and receiving telescope axes precisely aligned and parallel. Each telescope includes a primary reflector, a secondary reflector with a Cassegrainian focus behind the primary reflector and a tertiary retro-reflector behind an aperture at the vertex of the primary reflector.

Concentrating and collecting optical system using concave toroidal reflectors.

Abstract: An electromagnetic radiation source, such as an arc lamp, is located at a point displaced from the optical axis of a concave toroidal reflecting surface. The concave primary reflector focuses the radiation from the source at an off-axis image point that is displaced from the optical axis. The use of a toroidal reflecting surface enhances the collection efficiency into a small target, such as an optical fiber, relative to a spherical reflecting surface by substantially reducing aberrations caused by the off-axis geometry. A second concave reflector is placed opposite to the first reflector to enhance further the total flux collected by a small target.

Diffractive gratings for crystalline silicon solar cells—optimum parameters and loss mechanisms

Abstract: In this paper, we present guidelines for the design of backside gratings for crystalline silicon solar cells. We use a specially developed method based on a combination of rigorous 3D wave optical simulations and detailed semiconductor device modeling. We also present experimental results of fabricated structures. Simulation-based optimizations of grating period Λ and depth d of a binary grating and calculations of the optical and electrical characteristics of solar cells with optimized gratings are shown. The investigated solar cell setup features a thickness of dbulk = 40 µm and a flat front surface. For this setup, we show a maximum increase in short-circuit current density of ΔjSC = 1.8 mA/cm² corresponding to an efficiency enhancement of 1% absolute. Furthermore, we investigate different loss mechanisms: (i) an increased rear surface recombination velocity S0,b because of an altered surface caused by the introduction of the grating and (ii) absorption in the aluminum backside reflector. We analyze the trade-off point between gain due to improved optical properties and loss due to corrupted electrical properties. We find that, increasing the efficiency by 1% absolute due to improved light trapping, the maximum tolerable recombination velocity is S0,b(max) = 5.2 × 103 cm/s. From simulations and measurements, we conclude that structuring of the aluminum backside reflector should be avoided because of parasitic absorption. Adding a dielectric buffer layer between silicon and the structured aluminum, absorption losses can be tuned. We find that for a planar reflector, the thickness of a SiO2 buffer layer should exceed dSiO2 = 120 nm. Copyright © 2011 John Wiley & Sons, Ltd.

Yagi antenna having matching coaxial cable and driven element impedances

Abstract: A printed Yagi antenna of the present invention has a circuit board, a driven element having an impedance Ωd and being printed on the circuit board, a director element printed on the circuit board, a reflector element printed on the circuit board, a microstrip transmission line, and a coaxial cable having and impedance Ωc. The coaxial cable feeds the driven element via the miscrostrip transmission line and Ωc is approximately equal to Ωd. Further, the spacing between the reflector element, the driven element, and director elements are chosen so that an optimum balance is achieved between directional gain and performance sensitivity. The printed Yagi antenna has a partial folded driven element having a J shape which is grounded at the mid-point of the longest portion of the element. The configuration allows for a coaxial cable to be attached directly to the microstrip transmission line without the use of a matching network or balun.

Miniaturization of Slot Antennas Using Slit and Strip Loading

Abstract: The design of a miniaturized slot antenna with slit loading fed by the CPW line is proposed. It is seen that the loading slits can be located only on the feed side without degradation in cross-pol performance, unlike the microstrip-fed case. This releases the ground plane area above the slot for accommodating electronic circuitry and effectively reduces the antenna size. In addition, the resonant frequency in this case is reduced by a further 4.60%, compared to the slits on both sides. Another topology of the miniaturized antenna is investigated with the slits replaced by strips of metallization on the reverse side of the substrate, which leaves the ground plane area completely free. A high reduction in the slot resonant frequency is also observed in this case, with a reflector being used to increase the forward radiation.