Radio Telescope Reflectors (eBook)

Jacob W. M. Baars obtained the Ir- and Dr. Ir.-degrees in physics from the Technical University Delft in 1963 and 1970, respectively. After a three year stint at the National Radio Astronomy Observatory (USA) he joined the Netherlands Foundation for Radio Astronomy in 1966. There he participated in the construction and commissioning of the Westerbork Synthesis Radio Telescope and directed its operation from 1972. Upon moving to the Max-Planck-Institut für Radioastronomie in Bonn in 1975, he was project manager of two advanced millimeter wave radio telescope projects – the IRAM mm-telescope on Pico Veleta, Spain and the Heinrich Hertz Telescope on Mt. Graham, Arizona, USA. He served as Project Scientist during the definition and design phase of the Large Millimeter Telescope of Mexico/University of Massachusetts. In 1999 he joined the ALMA group at the European Southern Observatory in Garching, where he performed tasks in management, system engineering and in particular the design, construction and evaluation of two prototype submillimeter radio telescopes. Since his retirement he has acted as consultant to radio telescope projects and participated in project review committees, in particular the Square Kilometre Array.Hans Jürgen Kärcher obtained the Dipl.Ing. and Dr.-Ing. degrees in structural and mechanical engineering from the Technical University in Darmstadt in 1968 and 1974, respectively. He joined MAN Gustavsburg, (now MT Mechatronics) in 1974, initially as system engineer for telescopes and communication antennas. From 1986 up to retirement in 2006 he was head of research and development programs. From 2006 to now he is consultant for telescope mechanics, associated with MT Mechatronics, Mainz. He was project manager and/or lead system engineer for about 40 major telescope projects, optical as well as radio. Highlights were e.g. the 30m Millimeter Radio Telescope MRT IRAM in Spain, the 50m Large Millimeter Telescope LMT/GTM in Mexico, the 2.7m Stratospheric Observatory for Infrared Astronomy SOFIA in the US, and the 4m Advanced Solar Telescope ATST/DKIST on Maui, Hawaii.

Preface 7
Contents 10
Chapter 1: Introduction 14
Chapter 2: Evolution of the Telescope 21
2.1 Some History 22
2.1.1 Early Optical Telescope Efforts 22
2.1.2 Emergence of Electromagnetic (Radio) Waves 25
2.2 General Characteristics of Optical and Radio Telescopes 27
2.2.1 Introduction 27
2.2.2 Types of Telescope Mount and Optics 30
2.2.3 Alternative Geometrical Configurations 33
2.3 Technological Challenges for Radio Telescopes 34
2.4 Basic Specifications of a Reflector Radio Telescope 35
2.4.1 Reflector Precision 36
2.4.2 Pointing Precision 36
2.5 Summary 37
Addendum: Geometry of Optical Configuration 38
References 42
Chapter 3: Birth of Radio Astronomy 43
3.1 Early History of Radio Telescopes 44
3.1.1 Jansky´s Bruce Antenna 44
3.1.2 Reber´s Transit Paraboloidal Reflector 44
3.1.3 Würzburg Riese Radar Antenna 46
3.2 The First Large Radio Telescopes 48
3.2.1 Dwingeloo (NL) and Stockert (BRD) Telescopes 49
3.2.1.1 Dwingeloo 49
3.2.1.2 Stockert 51
3.2.2 A Comment on Accessibility of the Focal Point 54
3.2.3 Jodrell Bank (UK): Lovell Telescope (76 m) 54
3.2.4 Parkes (Australia) 64 m Telescope 59
3.2.5 NRAO (USA): 140-ft and 300-ft Telescopes 62
3.2.5.1 NRAO 140-ft Equatorial Telescope: An Expensive and Slow Project 64
3.2.5.2 NRAO 300-ft Transit Telescope: A Cheap and Quick Deal 67
3.2.6 The 120-ft Haystack Antenna of MIT Lincoln Laboratory 69
3.3 Conclusion 72
References 72
Chapter 4: Structural Design of Reflector Antennas: Homology 74
4.1 Introduction 75
4.2 The Design of Homologous Structures 75
4.3 The Design of a 65-m Homologous mm Telescope 81
4.4 The Effelsberg 100-m Radio Telescope 84
4.4.1 The German Proposal for a Giant Radio Telescope 84
4.4.2 A Comment on the Homologous Behaviour of a Structure 86
4.4.3 The Industrial Design Proposals 86
4.4.4 The Final Design and Realisation 89
4.5 Backup Structure and Deformation Patterns 91
4.5.1 The Design Approach of the Effelsberg Backup Structure 92
4.5.2 Interpretation of the Load Cases of the Effelsberg Reflector 95
4.5.2.1 Zenith Position 95
4.5.2.2 Horizon Position 96
4.5.3 Load Case Superposition 97
4.5.4 The Deformation Behaviour of the Effelsberg Reflector 98
4.5.5 Performance Limits of the Effelsberg Reflector Principle 103
4.6 Four-Point Reflector Support 106
4.6.1 Introduction 106
4.6.2 The Westerbork Array of 25-m Antennas 107
4.6.3 The MERLIN Antenna with a Perfect Four-Point Support 109
4.6.4 The Joined Four-Point Support of the IGN 40-m Telescope 114
4.7 Conclusion 117
References 117
Chapter 5: Emergence of Millimetre-Wavelength Telescopes 118
5.1 Into mm Wavelengths 119
5.2 The NRAO 36-ft Antenna 120
5.3 The IRAM 30-m Telescope (MRT) 123
5.3.1 Introduction: Performance Specification 123
5.3.2 The Design Selection 125
5.3.3 The Structural Concept of the MRT 129
5.3.4 The Deformation Behaviour of the MRT 132
5.3.4.1 Load Case in Zenith Position 132
5.3.4.2 Load Case in Horizon Position 133
5.3.4.3 The Deformation Behaviour of the Final Improved Design 133
5.3.5 Overall Surface Error of the Actual Telescope 136
5.3.6 Thermal Effects and Their Control 137
5.3.7 Conclusion 142
5.4 The Large Millimeter Telescope 143
5.4.1 Conceptual Design Phase 143
5.4.2 Towards a Final LMT Design 146
5.4.3 The Final Design of the LMT/GTM 147
5.4.4 Short Review of Surface Panel Technology 150
5.4.5 The Isostatic Reflector Segments of the LMT 151
5.4.6 Flexible Body Control (FBC) 152
5.4.7 Concluding Remark on the LMT/GTM 154
5.5 The Nobeyama 45-m Millimeter Telescope 155
5.6 Conclusion 156
Addendum: Thermal Effects and Their Control 156
References 162
Chapter 6: Submillimetre-Wavelength Telescopes 164
6.1 Introduction 165
6.2 Leighton Dish and CSO Telescope 166
6.3 CFRP Telescopes: IRAM 15-m and HHT 168
6.3.1 The IRAM Interferometer Antennas 168
6.3.2 The Heinrich Hertz (Submillimeter) Telescope (HHT) 170
6.4 Atacama Large Millimeter Array (ALMA) Antennas 173
6.4.1 Introduction 173
6.4.2 Test Program and Performance of the ALMA Prototype Antennas 176
6.4.3 Remark on the Circular BUS/ELC Interface Concept 179
6.4.4 Comparison of the Designs from AEM/EIE and Vertex 181
6.4.4.1 Comparison of Structural Design 181
6.4.4.2 Weight 184
6.4.4.3 Deformation Behaviour 185
6.4.4.4 Interpretation of the Astigmatism from Basic Structural Mechanics 186
6.4.4.5 Comparison of the Bearing and Drive Systems 190
6.4.4.6 Dynamic Behaviour, Structural Resonance Frequencies 191
6.4.5 Conclusion 192
References 194
Chapter 7: Alternative Reflector Geometries 195
7.1 Telescopes with Fixed Main Reflectors 196
7.2 The Giant Metrewave Radio Telescope (GMRT) in India 200
7.3 Large Horn Antennas 201
7.4 Offset Reflector Antennas 202
7.4.1 Introduction 202
7.4.2 Allen Telescope Array (ATA) 204
7.4.3 MeerKAT and Square Kilometre Array (SKA) 205
7.4.4 Green Bank Telescope (GBT) 208
Addendum: Remarks on Wheel-On-Track Systems 213
References 217
Chapter 8: Electromagnetic Aspects of the Reflector Antenna 218
8.1 Introduction 219
8.2 Radiation Pattern of a Circular Aperture 220
8.3 Major Parameters of the Reflector Antenna 222
8.4 Influence of Imperfections on Performance 224
8.4.1 Illumination, Spillover and Polarisation Efficiency 224
8.4.2 Radiation Efficiency 226
8.4.3 Small-Scale Surface Error (Scattering) Efficiency 226
8.4.4 Large-Scale Deformation: Representation by Zernike Polynomials 229
8.4.5 Blocking Efficiency 231
8.4.6 Lateral and Axial Defocus: Gain Loss 233
8.4.7 Beam Deviation Factor (BDF) 236
8.4.8 Conclusion 236
8.5 Measuring Antenna Parameters with Cosmic Sources 237
8.5.1 Antenna Gain and Beam Pattern 237
8.5.2 Antenna Pointing 238
8.6 Radio Holographic Measurement of Reflector Profile 240
8.7 Progress in Electromagnetic Design 242
8.7.1 Historical Introduction 242
8.7.2 Radio Astronomy and Communication Approaches Differ 243
8.7.3 Exploiting the Focal Plane 244
8.7.3.1 Multi-feed System with Independent Pixels 244
8.7.3.2 Phased-Array Feeds (PAF) 245
8.8 Conclusion 246
Addendum: Aberrations and Zernike Polynomials 247
References 250
Chapter 9: Concluding Review and a Dialogue on Management Aspects 252
9.1 Concluding Review 253
9.2 A Dialogue on Management Aspects 260
9.2.1 Customer and Contractor 261
9.2.2 Project Management and System Engineering 262
9.2.3 Technological Aspects 263
9.2.4 Industrialisation Aspects, Costs 264
9.2.5 Manufacturing in Foreign Countries 265
9.2.6 Product Delivery, Commissioning 266
Acronyms and Abbreviations 268
Glossary 271
Name Index 274
Subject Index 278