DEGREE PROJECT, IN ELECTROPHYSICS , SECOND LEVEL STOCKHOLM, SWEDEN 2014 Antenna for GNSS Reception in GEO-Orbit PATRICK MAGNUSSON KTH ROYAL INSTITUTE OF TECHNOLOGY ELECTRICAL ENGINEERING, SPACE AND PLASMA PHYSICS DEPARTMENT TRITA XR-EE-SPP 2014:003 www.kth.se Antenna for GNSS reception in GEO-orbit by Patrick Magnusson Master of Science Thesis XR-EE-SPP 2014:003 Royal Institute of Technology Department of Electrical Engineering Space and Plasma Physics Stockholm 2014 Page 2 Abstract There are a number of global navigation satellite systems (GNSS), in use or planed, which are used for navigation on earth but also for autonomous navigation of satellites in low earth orbit (LEO). It would be desirable to also have autonomous navigation in geosynchronous earth orbit (GEO) to reduce costs and make it possible to get higher accuracy on the position of the satellite. One part of the navigation system is the GNSS antenna which is examined in this master thesis. The specifications of the antenna were first decided and then three antenna alternatives were investigated in greater detail: a monofilar helix antenna, a three element circular array antenna and a twelve element circular array antenna. The result was that they would all work as a GNSS antenna in GEO but none could be judged to be the best under all circumstances. The size requirement for the mission and the used GNSS receiver would primarily decide which fits the mission best. Sammanfattning Det finns ett antal världstäckande navigeringssystem (GNSS), i användning och planerade, som används för navigation på jorden fast också för autonom navigation för satelliter i låg bana runt jorden. Det skulle också vara önskvärt att använda autonom navigation för satelliter i geostationär omloppsbana (GEO) för att reducera kostnaden och få högre positions noggrannhet. En del av navigationssystemet är GNSS antennen vilken är undersökt i detta examensarbete. Specifikationerna för antennen bestämdes först och sedan undersöktes tre olika antennalternativ i detalj: en monofilär helixantenn, en tre elements cirkulär gruppantenn och en tolv elements cirkulär gruppantenn. Resultatet var att alla alternativen skulle fungera som en GNSS antenn i GEO-bana fast inget av alternativen är bäst i alla förhållanden. Storlekskraven för uppdraget och vilken GNSS mottagare som skall användas påverkar vilket av alternativen som passar uppdraget bäst. Keywords GNSS antenna, GNSS, GPS, antenna, GEO, helical antenna, circular array, conical radiation pattern, link budget, monofilar helix, Page 3 Acknowledgement This master thesis was conducted at the company RUAG and I would like to thank RUAG and all the people working there for the opportunity and all the help I have received. I furthermore thank Johan Wettergren for being my supervisor at RUAG. I would also like to thank my supervisor at KTH, Nikolay Ivchenko, and the examiner at KTH, Tomas Karlsson. Acknowledgement goes to NASA for the cover picture of the first geosynchronous satellite, Syncom. Page 4 TABLE OF CONTENTS PAGE 1 INTRODUCTION ............................................................................... 6 1.1 Purpose ........................................................................................... 7 2 SPECIFICATIONS ............................................................................. 8 2.1 Performance .................................................................................... 8 2.1.1 Number of satellites tracked .......................................................... 9 2.1.2 GNSS receivers .......................................................................... 10 2.1.3 Position accuracy ........................................................................ 11 2.2 Bandwidth...................................................................................... 13 2.3 Radiation pattern ........................................................................... 16 2.3.1 Link budget ................................................................................. 17 2.3.2 Gain specifications ...................................................................... 20 2.4 Other electrical specifications ........................................................ 21 2.5 Mechanical and environmental requirements ................................. 22 2.6 Summary of the specifications ....................................................... 23 3 Antenna design ................................................................................ 24 3.1 Antenna trade-off table .................................................................. 24 3.2 Antenna type choice ...................................................................... 25 3.3 Array dimensioning ........................................................................ 26 3.3.1 Array element .............................................................................. 36 3.3.2 Final performance for the three element array ............................. 39 3.3.3 Final performance for the twelve element array ........................... 44 3.3.4 Mechanical construction .............................................................. 49 3.4 Helix dimensioning ........................................................................ 52 3.4.1 Single layer quadrifilar helix antenna ........................................... 52 3.4.2 Double layer quadrifilar helix antenna.......................................... 56 3.4.3 Monofilar helix antenna ............................................................... 60 3.4.4 Feed network .............................................................................. 77 3.4.5 Mechanical construction .............................................................. 81 3.5 Hispasat AG1 GPS Antenna .......................................................... 84 4 DISCUSSION .................................................................................. 86 4.1 Methods used and error sources ................................................... 86 4.1.1 Array field calculations ................................................................ 86 4.1.2 The helix HFSS model ................................................................ 86 4.2 Assumptions made ........................................................................ 87 4.3 Results .......................................................................................... 87 4.3.1 Link budget ................................................................................. 88 4.3.2 Array results ................................................................................ 88 4.3.3 Helix results................................................................................. 88 4.4 Fulfilment of specifications ............................................................. 89 4.4.1 Bandwidth ................................................................................... 89 4.4.2 Group delay................................................................................. 89 4.4.3 Cross polarization ....................................................................... 90 4.5 Future work ................................................................................... 90 4.6 Choice of antenna ......................................................................... 91 4.7 Impact on society and sustainability............................................... 92 5 CONCLUSION ................................................................................. 93 6 REFERENCES ................................................................................ 94 Page 5 Abbreviations A/D Analog-to-Digital ADS Advanced Design System C/N0 Carrier-to-Noise Density CNC Computer Numerical Control cx Cross EIRP Equivalent Isotropically Radiated Power ESA European Space Agency FDMA Frequency-Division Multiple Access FEM Finite Element Method GEO Geosynchronous Earth Orbit GIOVE Galileo In-Orbit Validation Element GLONASS Globalnaya navigatsionnaya sputnikovaya sistema GNSS Global Navigation Satellite System GOES Geostationary Operational Environmental Satellite GPS Global Positioning System HEO High Earth Orbit HFSS High Frequency Structural Simulator HPBW Half Power Beamwidth IGSO Inclined Geosynchronous Satellite Orbit IRNSS Indian Regional Navigational Satellite System LEO Low Earth Orbit LNA Low-Noise Amplifier LHC Left-Hand Circular MEO Middle Earth Orbit MMS Magnetospheric Multiscale Mission MoM Method of Moment N-GSO Non-Geosynchronous Orbit NASA National Aeronautics and Space Administration NF Noise Figure PEC Patch excited cup PSD Power Spectral Density QZSS Quasi-Zenith Satellite System RHCP Right-Hand Circular Polarization RMS Root-Mean-Square SMA SubMiniature version A TEAMSAT Technology, science and Education experiments Added to Maqsat. TM Transverse Magnetic VSWR Voltage Standing Wave Ratio XPD Cross Polarization Discrimination YES Young Engineer’s Satellite Page 6 1 INTRODUCTION The global navigation satellite systems (GNSS) work by having multiple satellites transmit their position and the time the position message was sent. The receiver can then decide its position by using the transmitted signal and knowledge of how long the signal has propagated. The most common receivers use a least square method where signals from four GNSS satellites are used to calculate the position. Three satellites are needed to decide the position and a fourth is needed to accurately decide the time at the receiver. The antenna on the GNSS satellite is pointing towards the earth with a narrow beam