The most fundamental obstacle encountered in design of satellite communication systems at frequencies above 10 GHz is attenuation by rain. The microwave power radiated toward an earth station, being limited by factors such as available primary power and size of antenna on the satellite, is insufficient, with present technology, to overcome the large attenuation produced by intense rain cells on the earth-space path. The resultant loss of signal makes for unreliable transmission. In what follows, methods of measurement of this attenuation at various frequencies and a technique called path diversity that substantially improves the reliability are presented. Other degradations produced by rain, such as depolarization, interference, increase in earth-station noise, and deterioration of earth-station antenna performance, are also discussed.

The role of rain in satellite communications

The cross polarized radiation for linearly polarized excitation and the beam displacement for circularly polarized excitation have been investigated for offset reflector antennas. Numerical calculations are given to illustrate the dependence upon the angle \theta_{0} between the feed axis and the reflector axis as well as upon the half-angle \theta_{c} subtended at the focus by the reflector. In the case \theta_{0} = \theta_{c} = 45\deg , measured results have been obtained for both linearly and circularly polarized excitations with a dual mode feed illuminating an offset paraboloid. The cross polarized radiation of horn reflector and open Cassegrainian antennas rises sharply to rather high values off the beam axis; however, in general, the maximum cross polarized radiation of offset reflector antennas can be made small by using a small angle between the feed and reflector axes. The cross polarization caused by offset is compared with that caused by an unbalanced feed pattern. The effect of the longitudinal current distribution and of departure of the surface from a paraboloid on cross polarization are also examined. The clarification of these cross polarization properties is found to be valuable in the design of reflector antennas.

Depolarization properties of offset reflector antennas

Conditions are derived that are useful for designing reflector antennas with excellent cross-polarization discrimination. These conditions ensure circular symmetry and absence of cross-polarization everywhere in the far field of an antenna, provided a suitable feed such as a corrugated horn is employed. The spherical wave radiated by the fundamental mode of such a feed has circular symmetry around the axis, and it is everywhere free of cross-polarization. An arbitrary sequence of N confocal reflectors (hyperboloids, ellipsoids, paraboloids) is combined with such a feed. It is shown that it is always possible to ensure circular symmetry (and absence of cross-polarization) in the antenna far field by properly choosing the feed axis orientation. If the final reflector is a paraboloid, a simple geometrical procedure can be used. It is also shown that the asymmetry caused by an arbitrary number of reflections can always be eliminated by properly introducing an additional reflection. An application to the problem of producing a horizontal beam using a vertical feed is discussed. Two arrangements are described that may be useful for radio relay systems.

Offset multireflector antennas with perfect pattern symmetry and polarization discrimination

Radio astronomy is an active and rapidly expanding field due to advances in computing techniques, with several important new instruments on the horizon This text provides a thorough introduction to radio astronomy and its contribution to our understanding of the universe, bridging the gap between basic introductions and research-level treatments It begins by covering the fundamentals physics of radio techniques, before moving on to single-dish telescopes and aperture synthesis arrays Fully updated and extensively rewritten, the fourth edition places greater emphasis on techniques, with detailed discussion of interferometry in particular, and comprehensive coverage of digital techniques in the appendices The science sections are fully revised, with new author Peter N Wilkinson bringing added expertise to the sections on pulsars, quasars and active galaxies Spanning the entirety of radio astronomy, this is an engaging introduction for students and researchers approaching radio astronomy for the first time

/pdf/an-introduction-to-radio-astronomy-3reqs3vamk.pdf

An Introduction to Radio Astronomy

A History of Engineering and Science in the Bell System

This paper describes the mechanical features of the horn-reflector antenna used for receiving signals reflected from the Project Echo balloon satellite and presents in some detail the electrical characteristics (radiation patterns and gain) measured at a frequency of 2390 mc. Theoretically derived characteristics which agree very well with the measurements are also presented; details of the calculations are given in the appendices.

A horn-reflector antenna for space communication

This paper describes the mechanical features of the horn- reflector antenna used for receiving signals reflected from the Project Echo balloon satellite, and presents in some detail the electrical characteristics (radiation patterns and gain) measured at a frequency of 2390 Mc. Theoretically derived characteristics which agree very well with the measurements are also presented; details of the calculations are given in the appendices.

/pdf/project-echo-horn-reflector-antenna-for-space-communication-2zjp0nvn0d.pdf

D. C. Hogg

Papers

A horn-reflector antenna for space communication

Project echo-horn-reflector antenna for space communication