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Some Aspects of Ground Station Antennas for Satellite Communication

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Some Aspects of Ground Station Antennas for Satellite Communication Some aspects of ground station antennas for satellite communication Citation for published version (APA): Maanders, E. J. (1975). Some aspects of ground station antennas for satellite communication. (EUT report. E, Fac. of Electrical Engineering; Vol. 75-E-60). Technische Hogeschool Eindhoven. Document status and date: Published: 01/01/1975 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 04. Oct. 2021 SOME ASPECTS OF GROUND STATION ANTENNAS FOR SATELLITE COMMUNICATION by E.J. Maanders Technische Hogeschool Eindhoven Eindhoven University of Technology Eindhoven Nederland Eindhoven Netherlands Afdeling Elektrotechniek Department of Electrical Engineering Some aspects of ground station antennas for satellite communication by E.J. Maanders T.H. Report 75-E-60 August 1975 ISBN 90 6144 060 This report has served as a thesis fo~ the degree of Doetor of Applied Science i contents page summary (English and Dutch) iii 1. General review 1 1.1. Introduction 1 1. 2. The antenna gain 3 1.3. The antenna temperature 5 1.4. Some antenna constructions 9 2. The classical cassegrain antenna 13 2.1. Introduction 13 2.2. Geometrical and optical relations 17 2.3. The antenna gain 20 2.3.1. Calculations using the scalar aperture method 20 2.3.2. The scalar aperture method with gain functions 23 2.4. Factors decreasing the antenna gain 26 2.4.1. Subreflector blockage 26 2.4.2. Diffraction 30 2.4.2.1. Diffraction phenomena introduced by the subreflector30 2.4.2.2. Diffraction efficiency of the subreflector 33 2.4.2.3. Diffraction and scattering of the subreflector supports 34 2.4.3. The antenna gain as a function of system parameters 35 2.5. Results and conclusions 36 Appendix 2.1 38 3. Aperture.blockage in dual reflector antenna systems 39 3.1. Introduction 39 3.2. Influence of obstructions on the directive 9ain pattern 40 3.2.1. Contribution by the subreflector 41 3.2.2. Contribution by the supports due to plane waves 43 3.2.3. Contribution by the supports due to spherical waves 45 3.2.4. The total directive gain pattern 9 (e,<p) 45 t 3.2.5. Results and conclusions 48 3.3. Power balance of the blocked aperture 50 3.4. Blockage efficiency in general 53 3.4.1. Basic expressions 53 3.4.2. optimizing the blockage efficiency 56 3.5. Typical examples of calculations of aperture blockage efficiency 59 3.5.1. Introduction 59 3.5.2. Uniform illumination 60 3.5.3. Tapered illumination 62 3.5.4. Results and conclusions 64 Appendix 3.1. Blockage by spherical waves 67 4. Radiation patterns of ref~ector antennas 69 4.1. Introduction 69 4.2. Radiation patterns calculated by physical optics 70 4.2.1. Geometry of the system 70 4.2.2. The primary source 71 4.2.2.1. The polarization of the primary source 71 4.2.2.2. The rectangular waveguide 72 4.2.2.3. The elementary dipole 73 4.2.3. The reflector 74 4.2.3.1. General considerations 74 4.2.3.2. Scattered radiation from the reflector 76 ii 4.2.3.3. Evaluation of the integral equations 77 4.2.3.4. Calculation of the total electric field 79 4.2.3.5. The gain function of the composite system 80 4.2.4. Discussion of some special cases 81 4.3. Some limitations of physical optics 83 4.3.1. Introduction 83 4.3.2. Some errors in calculating radiation patterns of reflector antennas using physical optics approximation 86 4.3.2.1. Mathematical models of antenna feed 86 4.3.2.2. Errors due to truncated feed patterns 87 4.3.3. The influence of the reflector diameter 92 4.3.4. The influence of the edge illumination 93 4.3.5. Conclusions 94 Appendix 4.1. Coordinate transformations 96 4.2. Calculations of current distribution at the paraboloid surface 97 4.3. Evaluation of the vector product n X (a X a.) 98 4.4. Calcul~tionlof back radiation of a paraboloid 100 5. Shaped double reflector systems 101 5.1. Introduction 101 5.2. The design of a circularly symmetrical antenna system 102 5.2.1. The system's geometry 102 5.2.2. Possible solution of the optimum blocking efficiency 106 5.2.3. The radiation patterns of shaped subreflectors 109 5.2.4. Conclusions 115 5.3. Mismatched shaped cassegrain systems 118 5.3.1. Aperture and spillover efficiency 118 5.3.2. Aperture illumination 122 5.3.3. The radiation pattern near the main axis 123 5.3.4. Subreflector blockage efficiency 125 5.3.5. Conclusions 125 6. Offset antennas 127 6.1. Introduction 127 6.2. The geometry of offset antennas 127 6.3. The gain factor of open cassegrain antennas 131 6.4. Cross polarization properties 135 6.4.1. Introduction 135 6.4.2. Aperture fields of reflector antennas illuminated by an electric dipole 136 6.4.3. Aperture fields of reflector antennas illuminated by a Huygens source 141 6.4.4. The polarization efficiency 143 6.4.5. A practical example 146 6.4.6. Conclusions 148 References 151 iii Summary Antennas for satellite communication ground stations have to meet very stringent requirements. Apart from the required antenna gain, which in the 4 - 6 GHz band can only be realized with apertures of 25 meter in diameter or more, the need for low noise is essential as well. In this report the advantages and disadvantages of the front-fed paraboloid and the cassegrain antenna are compared. It appears that the latter has much better noise properties. In Chapter 3 the problems with regard to blockage in double reflector systems are studied in detail. The influence of the subreflector and its supports on the near-in sidelobes is calculated. Different results may be expected in the ¢ = 0 and ¢ = 45° plane. Various examples have been worked out with regard to the blockage efficiency. A theory is further presented indicating that the blockage efficiency may be increased considerably, employing shaped double reflector systems. Shaping both main and subreflector a low subreflector edge illumination may be used, decreasing losses by diffraction and spillover. It further appears that in mismatched shaped systems large first side lobes are to be expected due to over illumination of the- edge of the main reflector. In Chapter 4 the physical optics approximation is discussed as a method to calculate the entire radiation pattern of a reflector antenna. A study has been made of the limitations and errors that occur with this method. Using theoretical truncated feed patterns, the directive gain pattern of the composite antenna system, integrated over the entire sphere does not yield 4TI, but more. In the last chapter the polarization properties of offset antennas are discussed. These properties are very unfavourable with respect to symmetrical front-fed paraboloids and cassegrain antennas. iv SAMENVATTING Op 12 Augustus 1960 bracht de NASA een ballon met een diameter van 30 meter in een baan rond de aarde om na te gaan of telecommunicatie door middel van een dergelijke satelliet mogelijkheden bood. Na de lancering van deze passieve Echo I satelliet heeft de satelliet communicatie zich stormachtig ontwikkeld. De experimenten zijn niet aIleen beperkt gebleven tot passieve satellieten,maar ook is. onderzoek verricht met aktieve satellieten zoals Courier, Telstar en Relay. Al deze satellieten doorliepen een relatief lage baan rond de aarde in enkele uren. Aantrekkelijker waren de satellieten die op een hoogte van 35.600 km boven de aarde gebracht konden worden en in precies 24 uur een baan rond de aarde beschreven. Zodoende newogen ze zich niet t.o.v. een observatiepunt op aarde. Bekend zijn de stationaire satellieten Syncom en vooral Early Bird, welke laatste op 5 april 1965 werd gelanceerd en de eerste commerciele ver­ binding tot stand bracht tussen Europa en Amerika voor telegrafie, telefo­ nie en televisie. Early Bird wordt tevens beschouwd als de eerste Intelsat satelliet waarvan thans vier generaties zijn gelanceerd.
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