Inflatable Antennas for Portable Direct Satellite Communication Naomi Mathers Bachelor of Engineering School of Electrical and Computer Engineering Science, Engineering and Technology Portfolio RMIT University Melbourne, Australia February 2010 Declaration I certify that except where due acknowledgement has been made, the work is that of the author alone; the work has not been submitted previously, in whole or in part, to qualify for any other academic award; the content of the thesis is the result of work which has been carried out since the official commencement date of the approved research program; any editorial work, paid or unpaid, carried out by a third party is acknowledged; and, ethics procedures and guidelines have been followed. Naomi Mathers 8 February 2010 ii Acknowledgements I would like to acknowledge the support of my family and friends. Without their encouragement and patience would not have been possible for me to undertake this project. I would like to thank Prof. Andrew Jennings from RMIT University supervising this project in its closing stages; his advice and experience were invaluable. I would like to thank Assoc. Prof. Lachlan Thompson and Dr. Kamran Ghorbani from RMIT University for their supervision during the early stages of this project. I would also like to acknowledge Dr. Ghorbani for the design of the microstrip patch that was used to feed the gossamer horn presented in this thesis. I would like to thank Mr. David Welch from RMIT University for manufacturing the microstrip patch and the rigid horns used in the testing. I would like to thank Mr Terry Rosewarne from RMIT University for manufacturing the composite parabolic reflector used as the comparison for the inflatable antenna. I would like to thank Dr. Christophe Granet from CSIRO’s Electromagnetics and Antennas Group, for completing the CST Microwave Studio simulations presented in this thesis. Finally, I would like to thank Mr. John Wright from Visypak Australia for donating the material used to manufacture the antenna presented. iii Contents Declaration..................................................................................................................... ii Acknowledgements........................................................................................................ iii List of figures................................................................................................................. vii List of Tables.................................................................................................................. xiii Glossary of Symbols...................................................................................................... xiv Abstract.......................................................................................................................... 1 Introduction................................................................................................................... 2 1. Background.............................................................................................................. 4 1.1 Satellite-based Personal Communication Systems (SPCS)................................ 4 1.2 Existing land-based direct satellite communication technology......................... 4 1.2.1 Portable rigid parabolic dish antennas.................................................... 5 1.2.2 Articulated parabolic dish antennas........................................................ 6 1.3 Existing Space-based Technology...................................................................... 8 1.3.1 Rigid space-based parabolic dish antennas............................................ 8 1.3.2 Articulated space-based parabolic dish antennas................................... 9 1.4 Inflatable Structures in the Space Environment................................................. 11 1.4.1 Non precision inflatable structures in the space environment............... 12 1.4.2 Inflatable antennas in the space environment........................................ 12 1.4.2.1 Current development of space-based inflatable antennas............... 16 1.4.3 Disadvantages of Using Inflatable Structures in the Space Environment 17 1.5 Comparison of Space-based Parabolic Antenna Structures............................. 18 1.6 Inflatable Antennas in the Terrestrial Environment.......................................... 20 2. Design..................................................................................................................... 22 2.1 Material............................................................................................................. 22 2.2 Pressure vessels................................................................................................ 23 2.2.1 Parabolic reflector................................................................................ 26 2.2.2 Conical canopy..................................................................................... 28 2.2.3 Torus.................................................................................................... 30 2.3 Internal pressure............................................................................................... 31 2.4 Rigidizing inflatable structures........................................................................ 33 2.5 Antenna configuration...................................................................................... 33 iv 2.5.1 Skin depth............................................................................................. 36 2.5.2 Basic antenna parameters..................................................................... 37 2.5.3 Conical feed horn for prime focus antenna.......................................... 39 2.5.3.1 Phase centre.................................................................................... 49 2.5.4 Prime focus antenna............................................................................. 50 2.6 Cassegrain antenna and horn............................................................................ 53 2.7 Microstrip patch.............................................................................................. 56 3. Fabrication Methodology and Measurement Set-Up...................................... 58 3.1 Antenna design to be tested............................................................................. 58 3.2 Simulation....................................................................................................... 60 3.3 Material testing................................................................................................ 61 3.3.1 Structural properties............................................................................ 61 3.3.2 Electromagnetic properties................................................................... 62 3.4 Microstrip patch.............................................................................................. 62 3.5 Feed horn......................................................................................................... 65 3.6 Parabolic reflector............................................................................................ 70 4. Results................................................................................................................... 81 4.1 Simulation........................................................................................................ 81 4.1.1 Microstrip patch................................................................................... 81 4.1.2 Conical horn fed by microstrip patch for prime focus antenna............ 83 4.1.3 Conical feed horn fed by microstrip patch for Cassegrain antenna...... 86 4.1.4 Impact of support struts, ribs and pillowing on antenna performance. 89 4.1.4.1 Rigid parabolic reflector fed by point source................................. 90 4.1.4.2 Impact of single strut on the radiation patterns.............................. 91 4.1.4.3 Impact of three struts on the radiation patterns............................. 92 4.1.4.4 Comparison of point source and horn feed.................................... 93 4.1.4.5 Impact of pillowing in an antenna with 8 ribs................................ 94 4.1.4.6 Impact of pillowing in an antenna with 12 ribs.............................. 95 4.1.4.7 Impact of pillowing in an antenna with 16 ribs.............................. 96 4.2 Material Testing................................................................................................ 97 4.2.1 Structural properties............................................................................. 97 4.2.2 Electromagnetic properties................................................................... 97 4.3 Microstrip patch............................................................................................... 98 v 4.4 Gossamer horn.................................................................................................. 100 4.5 Parabolic reflector........................................................................................... 103 5. Evaluation............................................................................................................ 107 5.1 Simulation....................................................................................................... 108 5.2 Material.......................................................................................................... 115 5.2.1 Material physical properties............................................................... 118 5.2.2 Material electromagnetic properties.................................................. 119 5.3 Testing of the inflatable antenna.................................................................... 119 5.3.1 Microstrip patch................................................................................. 120 5.3.2 Gossamer horn................................................................................... 121 5.3.2.1 Pattern making............................................................................. 121 5.3.2.2 Assembly...................................................................................... 122 5.3.2.3 Tape............................................................................................. 123 5.3.2.4 Heat welding................................................................................. 124 5.3.2.5 Testing.......................................................................................... 125 5.3.3 Inflatable antenna............................................................................... 131 5.3.3.1 Pattern making............................................................................. 131 5.3.3.2 Forming the parabolic reflector.................................................... 132 5.3.3.3 Assembly...................................................................................... 133 5.3.3.4 Testing.......................................................................................... 135 6. Future Work....................................................................................................... 145 7. Other Applications............................................................................................. 151 7.1 Portable direct satellite communication on the moon.................................... 151 7.2 Radio astronomy from the moon.................................................................... 152 Conclusions............................................................................................................... 154 References................................................................................................................. 155 Bibliography............................................................................................................. 159 List of Publications................................................................................................... 161 vi List of figures Fig. 1: Typical military Communications-on-the-Halt (COTH) ground station (image courtesy of US DoD) Fig. 2: Typical military Communications-on-the-Pause (COTP) ground station (image courtesy of US DoD) Fig. 3: Typical articulated mesh, or umbrella, parabolic dish antenna (image courtesy of US DoD) Fig. 4: Typical petal deployable parabolic dish antennas (image courtesy of Thales and US DoD) Fig. 5: Galileo High Gain Antenna (image courtesy of NASA) Fig. 6: Galileo High Gain Antenna in the stowed position (image courtesy of NASA) Fig. 7: Galileo High Gain Antenna in the fully deployed position (image courtesy of NASA) Fig. 8: Weight comparison of a range of deployable antennas (source JPL) Fig. 9: Stowed volume comparison of a range of deployable antennas (source JPL) Fig. 10: Echo 1A (image courtesy of NASA) Fig. 11: L’Garde Inflatable Antenna Experiment (IAE) in orbit (image courtesy of L’Garde) Fig. 12: L’Garde Inflatable Antenna Experiment (IAE) stowed ready for launch (image courtesy of L’Garde) Fig. 13: Deployment of the L’Garde Inflatable Antenna Experiment (IAE) (images courtesy of L’Garde) Fig. 14: GATR Technologies inflatable antenna (images courtesy of GATR) Fig. 15: Layout of inflatable antenna Fig. 16: Membrane forces in parabolic reflector Fig. 17: Membrane stress distribution in conical canopy Fig. 18: Membrane stress distribution in torus Fig. 19: Layout of prime focus parabolic dish antenna Fig. 20: Aperture efficiency as a function of reflector half-angle [source: Constantine A. Balanis, Antenna Theory: Analysis and Design (2nd Ed.), John Wiley & Sons, 1997] vii Fig. 21: Taper and spillover efficiency as a function of reflector half-angle [source: Constantine A. Balanis, Antenna Theory: Analysis and Design (2nd Ed.), John Wiley & Sons, 1997] Fig. 22: Relative field strength of feed pattern along reflector edge bounds as a function of primary feed pattern number [source: S. Silver (ed.), Microwave Antenna Theory and Design, MIT Radiation Lab. Series Vol. 12, McGraw-Hill, New York, 1949] Fig. 23: H-plane universal pattern for a conical horn [source: A. D. Olver, P. J. B. Clarricoats, A. A. Kishk and L. Shafai, Microwave Horns and Feeds, IEE Electromagnetic Wave Series 39, IEEE Press 1994] Fig. 24: E-plane universal pattern for a conical horn [source: A. D. Olver, P. J. B. Clarricoats, A. A. Kishk and L. Shafai, Microwave Horns and Feeds, IEE Electromagnetic Wave Series 39, IEEE Press 1994] Fig. 25: Layout of conical horn Fig. 26: Universal phase-centre curves for conical horns [source: A. D. Olver, P. J. B. Clarricoats, A. A. Kishk and L. Shafai, Microwave Horns and Feeds, IEE Electromagnetic Wave Series 39, IEEE Press 1994] Fig. 27: Dimensions of prime focus antenna and clear canopy required to position the phase centre of the feed horn at the focal point of the reflector Fig. 28: Layout of Cassegrain antenna Fig. 29: Cassegrain antenna horn design Fig. 30: Dimensions of microstrip patch Fig. 31: Testing electromagnetic properties using network analyser Fig. 32: Schematic of test setup in anechoic chamber Fig. 33: Microstrip patch Fig. 34: Aluminium feed horn Fig. 35: Patterns for prime focus antenna feed horn components Fig. 36: Cutting pattern pieces for prime focus antenna feed horn components Fig. 37: Assembly of individual horn components with the assistance of shaped plugs Fig. 38: Transfer tape applicator Fig. 39: Lap joint used to assemble feed horn components Fig. 40: Individual components of feed horn Fig. 41: Hot glue gun used to assemble feed horn pieces Fig. 42: Assembled gossamer horn with Aluminium horn viii Fig. 43: Gossamer horn with microstrip patch Fig. 44: Aluminium horn with microstrip patch Fig. 45: Simulation of increasing antenna pressure without rim support Fig. 46: Reflector plug and rigid composite reflector dish manufactured using reflector plug Fig. 47: Rigid reflector dish fed by gossamer horn in anechoic chamber Fig. 48: Pattern for one of six identical gores used to construct the gossamer reflector dish Fig. 49: Lap joint used to assemble gores in parabolic dish reflector Fig. 50: Assembly of gossamer reflector Fig. 51: Clear canopy pattern Fig. 52: Conical canopy pattern and clear polyester thin film Fig. 53: Conical feed horn and adapter. Conical feed horn installed in the apex of the clear canopy Fig. 54: Inflatable antenna with gossamer horn mounted on rigid frame Fig. 55: Inflatable antenna with gossamer horn mounted on rigid frame in anechoic chamber Fig. 56: Inflatable antenna with gossamer horn mounted on rigid frame in anechoic chamber Fig. 57: Inflatable antenna with gossamer horn stowed for travel Fig. 58: Simulated microstrip patch Fig. 59: Simulated S11 (Return Loss) of the patch Fig. 60: Simulated horn for prime focus antenna fed by microstrip patch Fig. 61: Simulated S11 (Return Loss) of the conical horn fed by microstrip patch Fig. 62: Simulated co and cross polar radiation patterns of a conical horn fed by a microstrip patch at 12.50 GHz. (Peak=13.72 dBi) Fig. 63: Simulated horn fed by TE11 circular-waveguide mode Fig. 64: Simulated co and cross polar radiation patterns of a conical horn fed by a TE11 circular-waveguide mode Fig. 65: Simulated horn for Cassegrain antenna fed by microstrip patch Fig. 66: Simulated S11 (Return Loss) of the conical horn for Cassegrain antenna fed by microstrip patch Fig. 67: Simulated radiation pattern of conical horn for Cassegrain antenna fed by microstrip patch at 12.50 GHz. (Peak=19.26 dBi) ix Fig. 68: Simulated radiation pattern of conical horn for Cassegrain antenna fed by a TE11 circular waveguide mode at 12.5 GHz (Peak=19.2 dBi) Fig. 69: Simulated radiation pattern of single rigid parabolic reflector fed by point source (Black: E-field / Blue: H-field / No cross polar) Fig. 70: Simulated radiation pattern of single rigid parabolic reflector fed by point source supported by single 0.005m diameter strut (Black: E-field / Red: H-field / Blue: cross polar (E) / No cross polar (H)) Fig. 71: Simulated radiation pattern of single rigid parabolic reflector fed by point source supported by three 0.005m diameter strut (Black: E-field / Blue: H-field / Green: cross polar (E) / No cross polar (H)) Fig. 72: Simulated radiation pattern of single parabolic reflector fed by point source, with no ribs and no pillowing (E-field) Fig. 73: Simulated radiation pattern of single parabolic reflector fed by conical horn, with no ribs and no pillowing (E-field) Fig. 74: Simulated radiation pattern of single parabolic reflector fed by point source, with 8 ribs and no pillowing (E-field) Fig. 75: Simulated radiation pattern of single parabolic reflector fed by conical horn, with 8 ribs and no pillowing (E-field) Fig. 76: Simulated radiation pattern of single parabolic reflector fed by point source, with 8 ribs and pillowing (E-field) Fig. 77: Simulated radiation pattern of single parabolic reflector fed by conical horn, with 8 ribs and pillowing (E-field) Fig. 78: Simulated radiation pattern of single parabolic reflector fed by point source, with 12 ribs and no pillowing (E-field) Fig. 79: Simulated radiation pattern of single parabolic reflector fed by conical horn, with 12 ribs and no pillowing (E-field) Fig. 80: Simulated radiation pattern of single parabolic reflector fed by point source, with 12 ribs and pillowing (E-field) Fig. 81: Simulated radiation pattern of single parabolic reflector fed by conical horn, with 12 ribs and pillowing (E-field) Fig. 82: Simulated radiation pattern of single parabolic reflector fed by point source, with 16 ribs and no pillowing (E-field) Fig. 83: Simulated radiation pattern of single parabolic reflector fed by conical horn, with 16 ribs and no pillowing (E-field) x