Cassegrain antenna

About: Cassegrain antenna is a research topic. Over the lifetime, 3207 publications have been published within this topic receiving 28278 citations.

A Reflector Antenna Concept Robust Against Feed Failures for Satellite Communications

Abstract: Since the first communications satellites have been launched to space with the beginning of the 1960s, these systems have undergone a rapid development. Amongst others, this development is driven by an increasing number of subscribers exchanging larger and larger data volumes. This need of data capacity cannot be satisfied alone by raising the sheer number of communications satellites, but requires powerful individual systems, which operate reliably and are cost effective at the same time. In this context two requirements on the communications antenna are the provision of high directional gain and robustness in terms of beam stability. Classically, large unfurlable mesh reflector antennas in conjunction with feed arrays are adopted to illuminate a certain region on ground with high gain. An inherent problem of such reflector-feed configurations is that these systems are prone to feed element failures. In the worst case, this could result in a ‘blind’ spot, where no communication is possible. This paper introduces a robust antenna concept, which combines the virtue of reflector antennas, namely the large aperture, with the advantage of direct radiating planar array antennas, which is the beam stability in the presence of element failures. In order to unfold its full potential this concept makes use of digital beamforming techniques, which allow to control the illumination in a flexible way.

Offset Cassegrain Earth Station Antenna for the Japanese Domestic Satellite Communication System

Abstract: Offset reflector antennas have advantages for communication systems because they are not severely subject to blocking. Difficulties mainly arising from structual asymmetries have inhibited the realization of an offset reflector antenna with a large aperture for commercial use. This paper describes the design of an offset Cassegrain earth station antenna for the Japanese domestic satellite communication system. Antenna measurements showed 76 and 69 percent aperture efficiencies at 20 and 30 GHz, respectively, less than -20 dBi wide angle directivity and an 18 K noise temperature in operating conditions. Performances are far superior to conventional axisymmetrical earth station antennas. The antenna was reassembled on a telephone office building after the measurements. The antenna gain was reconfirmed there, using the sun as a radio frequency source. Experiments show that the earth station antenna and a terrestrial antenna can be placed on the same building without serious interference.

Large angular electronic beam steering antenna for space application

Abstract: In order to replace a large phased array, antenna subsystems usually combine a large reflector, a small phased array, and an arrangement of small reflectors, which form a large image of the array over the main reflector aperture. This way one can get a large-aperture electronically steerable antenna, using only a small phased array. The basic idea of such an antenna is to use the two offset fed paraboloidal reflectors in such a way that the off-axis aberrations tend to cancel each other. The implementation of a correcting lens in the common focal plane is proposed. The objective is to enlarge the off-axis aberration matching domain, so that the scanning capability is increased (15 beamwidth/40 beamwidth). As an application, a Ka-band mission is discussed for a 3-m-diameter antenna (26 GHz) with a field of view of +or-10 degrees as required for the Data Relay Satellite. It is confirmed that the scanning limitation of the offset fed Gregorian antenna has been relaxed from approximately 15 beamwidth to 40 beamwidth by the use of a corrective lens implemented in the common focal area. >

The curved passive reflector

Abstract: The curved passive reflector is analyzed theoretically by the aperture-field method and the results are presented in the form of gain characteristics and radiation patterns. It is seen that curving the reflector produces a focusing effect in addition to the basic diffraction phenomenon, thereby providing increased gain as compared with the flat reflector. The limiting value for the flat reflector gain is 6 db while the gain of the curved reflector increases continually with reflector size when properly illuminated. Radiation patterns are computed and it is shown that the effect of reducing tower height is to widen the main lobe and to move the side lobes outward and depress them. It is concluded that, in general, the curved reflector causes lower side lobes than the flat reflector. The dish illumination is shown to be relatively unimportant with respect to the total antenna gain but the side lobe levels are reduced when the dish illumination is made more uniform.

Asymptotic and full wave simulation models for compensated compact range design and analysis

Abstract: Compensated compact ranges (CCR) can be considered a standard for real-time and high accuracy measurements for spacecraft antenna and payload testing. A compact range is an indoor antenna test facility which consists mainly of a large antenna reflector (single, dual, or even multiple reflector arrangements are possible) which is illuminated by an appropriate feed system and reflected via the reflector(s) into a test zone area, the so-called quiet zone (QZ). This test zone is located close to the reflector in order to utilize the radiated near-field distribution characteristic. The interesting fact is that this near-field zone shows a similar behavior in a limited area as it would be at the classical far-field distance. Since the reflector size is finite the reflector edges produce diffracted field contributions which are undesirable at the quiet zone. In order to predict the performance of the quiet zone numerical simulations are required and mandatory for a state-ofthe-art facility. Available appropriate electromagnetic field solvers can be distinguished between (a) full wave and (b) asymptotic methods. Full wave techniques for the computation of scattered and diffracted electromagnetic fields are computationally intensive and traditionally impractical to handle for CCR design. Due to this fact, asymptotic methods have been traditionally used during the design of such facilities. These methods offer acceptable accuracy to solve scattering problems at short wavelengths but their precision becomes more than questionable for objects which size is comparable to the wavelength. Astrium's CCR dimensions are typically of several hundreds of lambdas at higher frequencies. In the past decade, significant advances related to CPU/memory costs reduction, parallel computation, and new formulations based on Multilevel Fast Multipole Methods allow full-wave calculations for increasing frequencies. This enables verification of asymptotic methods by comparison with full wave calculations.