China
Africa
Explore chapters and articles related to this topic
Antennas
Published in J. Dunlop, D. G. Smith, Telecommunications Engineering, 2017
The primary feeds normally used are shown in Fig. 7.15. The dipole, with parasitic reflector to prevent radiation in the forward direction, has a less directive radiation pattern than the horn antenna, and therefore illuminates the edge of the reflector too strongly, but it has a much smaller supporting structure than that required for the horn, and so does not block as much of the reflected wave. To reduce this blocking by the support, a Cassegrain antenna is sometimes used, particularly in receiving applications. The Cassegrain antenna (Fig. 7.16) consists of a primary horn feed, set in the surface of the reflector, and a sub-reflector of hyperbolic shape placed just in front of the focus of the parabola. Energy from the horn strikes the sub-reflector and is then redirected to the surface of the parabolic dish. The supports used for the sub-reflector are much less robust than the waveguide feed necessary for a horn-type primary source.
Communications
Published in Diego Galar, Uday Kumar, Dammika Seneviratne, Robots, Drones, UAVs and UGVs for Operation and Maintenance, 2020
Diego Galar, Uday Kumar, Dammika Seneviratne
In a Cassegrain antenna (see Figure 7.15), the primary feed radiator is positioned around an opening near the vertex of the paraboloid instead of at the focus. A Cassegrain feed system employs a hyperboloid secondary reflector, one of whose foci coincides with the focus of the paraboloid. The feed radiator is aimed at the secondary hyperboloid reflector or sub-reflector. The radiations emitted from the feed radiator are reflected from the Cassegrain secondary reflector, illuminating the main paraboloid reflector as if they had originated from the focus. Then the paraboloid reflector colliminates the rays as usual (Dhande, 2009).
Earth Stations
Published in A.F. Inglis, A.C. Luther, Satellite Technology: An Introduction, 1997
Dual-reflector antennas come in a variety of configurations, depending on the shape of the two reflectors. If the subreflector is convex toward the main reflector as in Figure 4.1, it is known as a Cassegrain antenna. If it is concave, it is known as a Gregorian. In still another variation known as the Gregux, the subreflector consists of a concave ring.
Optimizing Dimensions of Cassegrain Antenna System with Large Magnification Factor
Published in IETE Journal of Research, 2023
In Cassegrain antenna, parabolic subreflector acts as an obstacle against the radiated waves after secondary reflection from the main reflector. In this case, the effect of blockage must be included in the antenna gain and so (8) must be multiplied by another factor called blockage efficiency . When the blocked area be and the physical aperture area of antenna be , we have . So if becomes larger, naturally the blockage efficiency and thereafter the antenna gain gets smaller. So must be designed as low as possible.