GPS/GNSS Antennas В. Rama Rao W. Kunysz R. Fante К. McDonald ARTECH HOUSE BOSTON LONDON artechhouse.com
Contents Preface xv CHAPTER 1 Introduction to GNSS Antenna Performance Parameters 1 1.1 Role of an Antenna in GNSS and its Key Requirements 1 1.2 Summary of Satellite Navigation Systems 2 1.2.1 GNSS 3 1.2.2 Regional Satellite Navigation Systems 3 1.2.3 Satellite-Based Augmentation Systems 4 1.3 Polarization and Radiation Pattern of a GNSS Antenna 5 1.3.1 Polarization Efficiency and Polarization Mismatch Loss 11 1.3.2 Effect of Axial Ratio on the Reception of Satellite Signals by the Receiving Antenna 15 1.3.3 Effect of Axial Ratio of a GNSS Antenna on Reception of Different Types of Multipath Signals 15 1.4 Directivity and Gain of a GNSS Antenna 17 1.4.1 RHCP Gain of a GNSS Antenna for an Optimum Radiation Pattern Defined by Its Low Elevation Masking Angle 18 1.4.2 Relationship between Beamwidth, Aperture Size, and Directive Gain of a GNSS Antenna 21 1.4.3 Effect of Minimum Gain Beamwidth and Antenna Pattern Contour on GDOP 23 1.5 Phase Center of a GNSS Antenna 29 1.5.1 Carrier Phase Windup 32 1.6 Group Delay Variation in GNSS Antennas 35 1.6.1 Requirements for Group Delay Variation with Frequency 36 1.6.2 Group Delay Variation with Aspect Angle 37 1.7 Propagation and Multipath Errors in GNSS Measurements 38 1.8 Antenna-Induced Errors in GNSS Measurements 39 1.8.1 Group Delay Error 39 1.8.2 Phase Center Error 39 1.8.3 Carrier Phase Windup Error 40 1.9 Differencing Techniques for Removal of Bias Errors in GNSS Measurements 40 VII
VIII Contents 1.10 Differencing of GPS Data for Removal of Antenna-Induced Carrier Phase Errors 41 1.11 Differential GPS and RTK Measurements 43 1.12 Techniques for Removal and Estimation of Carrier Phase Windup Errors Caused by a Rotating Antenna 44 1.13 The Susceptibility of a Commercial GPS C/A Code Receiver to Interference and Jamming 45 1.13.1 LightSquared Transmissions 47 1.13.2 Civil GPS Jammers 47 1.14 Architecture of a GNSS Receiver 48 1.13.1 Software Defined Radio (SDR) 49 1.15 Effects of Interference and Jamming on Tracking Loop Thresholds of a GPS Receiver 50 1.16 Carrier to Noise Ratio of an Antenna and Receiver Front End at "Masking Elevation" of 5 in the GPS and Galileo Frequency Bands for Quiescent Conditions (Absence of Interference or Jamming) 53 1.17 Effective Carrier-to-Noise Ratio in the Presence of Interference or Jamming 57 1.17.1 Effects of Jamming or Interference on a GPS Commercial C/A Code Receiver 58 References 59 CHAPTER 2 FRPAs and High-Gain Directional Antennas 63 2.1 Categories of GNSS Antennas 63 2.1.1 FRPA 64 2.2 Microstrip Antennas 66 2.2.1 Selection of the Dielectric Substrate for Microstrip Antennas 69 2.2.2 Effects of Surface Waves on Microstrip GNSS Antennas 70 2.2.3 Design of Dual-Probe-Fed RHCP Single-Band Microstrip GNSS Antenna 71 2.2.4 A Parametric Study of a Single-Band RHCP Square-Shaped Microstrip Antenna 73 2.2.5 GNSS Dual-Band Stacked Microstrip Patch Antennas 87 2.2.6 Feed Techniques for Generating RHCP in GNSS Microstrip Antennas 92 2.2.7 Circular RHCP Microstrip Antenna 103 2.2.8 Annular Ring RHCP GNSS Microstrip Antenna 108 2.2.9 Mutual Coupling Effects in GNSS Microstrip Antenna 112 2.2.10 Phase and Group Delays in GNSS Microstrip Antennas 114 2.2.11 Advantages and Disadvantages of Microstrip Antennas for GNSS Applications 117 2.3 Quadrifilar Helix Antenna 119 2.3.1 Self-Phasing QHA 119 2.3.2 Externally Phased QHA 128
2.3.3 A Summary of the Advantages and Disadvantages of QHAs for GNSS 131 2.4 Hexafilar Slot Antenna for GPS 133 2.5 Planar and Drooping Bow-Tie Turnstile Antennas for GNSS 134 2.5.1 End-Fire Array of Turnstile Antennas for Multipath Limitation 136 2.6 Directional GNSS Antennas 136 2.6.1 Helical Antennas 136 2.6.2 Helibowl Multipath Limiting Antenna 143 2.6.3 Hemispherical Helix Antenna and Its Use in a GPS Beamforming Array 144 2.6.4 High-Gain Reflector Antennas for Monitoring GNSS Signals 144 2.7 Beamforming Antenna Arrays 147 References 152 CHAPTER 3 Multiband, Handset, and Active GNSS Antennas 157 3.1 Introduction 157 3.2 Multiband GNSS Antennas 158 3.2.1 Current and New Satellite Navigations Systems 158 3.2.2 Advantages Offered by Multiple GNSS 161 3.3 Current Technology for Multiband GNSS Antennas 163 3.4 Performance Requirements for Geodetic-Grade Multiband GNSS Antennas 164 3.4.1 Phase Center Stability Requirements and Calibration of Multiband GNSS Antennas 165 3.4.2 Multipath Rejection Ratio and FBR 167 3.4.3 Size and Weight Requirements for Rover Antennas Used in DGPS and RTK 168 3.5 Geodetic-Grade Multiband GNSS Antennas Using New Ground Plane Technology 169 3.5.1 Wideband 2D GNSS Cutoff and Noncutoff Corrugated Ground Planes 171 3.5.2 NovAtel GNSS-750 and Leica AR25 Wideband GNSS Antenna with Hemispherical Choke-Ring Ground Plane 174 3.5.3 Trimble's Zephyr Geodetic 2 GNSS Antenna with Resistivity Tapered Ground Plane 175 3.5.4 Wideband and Low-Profile GNSS Antenna on an AMC/EBG Ground Plane 177,3.6 GNSS Geodetic-Grade Antennas Based on Spiral Antenna Technology 179 3.6.1 Introduction to the Design of Spiral Antennas 180 3.6.2 Roke Manor's GNSS Multiband Cavity-Backed Archimedean Four-Arm Spiral Antenna with a Special Ground Plane 182 3.6.3 Ultrawideband GNSS Antenna Based on SMM Technology byweo 184 3.6.4 NovAtel's GPS-704X Wideband GNSS Pinwheel Antenna 185
3.6.5 Wideband Conical Spiral Antenna for GPS and Galileo 188 3.7 Microstrip and Other Wideband Antennas Designs for GNSS 190 3.7.1 Wideband GNSS Microstrip Antenna Covering 1.164 to 1.610 GHz 190 3. 8 GNSS Antennas for Handset 193 3.8.1 Techniques for Locating Wireless Devices 193 3.8.2 Fundamentals of A-GPS 194 3.9 Design of Handset Antennas: Requirements and Technical Challenges 196 3.9.1 Size, Appearance, Cost, Weight, and Functionality 196 3.9.2 Influence of Receiver Chassis on Bandwidth of Cell Phone Antennas 198 3.9.3 Polarization and Radiation Pattern Requirements of GPS Cell Phone Antennas 199 3.9.4 Isolation Techniques to Mitigate EMI/EMC Effects on GPS Antennas in Cell Phones 200 3.9.5 User Effects on Handset Antennas 202 3.10 Representative GPS Antenna Designs Used in Handsets 206 3.10.1 Dielectric Chip GPS Handset Antennas Using Ceramic and LTCC Substrates 206 3.10.2 Basic PIFA and Design Variations of a PIFA 211 3.10.3 Isolated Magnetic Dipole for GPS Handsets by Ethertronics 213 3.10.4 Coplanar Balanced Dipole Antenna for Handsets by Antenova Ltd. 214 3.10.5 Miniaturized Ceramic Loaded QHA for Handsets 215 3.11 Active GNSS Antennas and the Use of the G/T Ratio as Its Performance Metric 216 3.12 G/T Measurement of an Active GNSS Antenna 220 3.12.1 Technique for G/T Measurement of Active GPS Antennas 221 References 222 CHAPTER 4 Adaptive GPS Antennas 231 4.1 Introduction 231 4.2 Two-Element Adaptive Array 231 4.2.1 Theory of Operation 231 4.2.2 Effect of Bandwidth and Gain for Ideal Antennas 233 4.2.3 Effect of Dispersive Errors (Channel Mismatch) 236 4.2.4 Effect of Multipath 238 4.3 Space-Time Adaptive Array 239 4.3.1 Introduction 239 4.3.2 Calculating the Adaptive Weights 241 4.3.3 Frequency-Angle Response 246 4.4 Covariance Matrix Estimate 249 4.5 Dual-Polarized Antenna Array 252 4.6 Performance Measures 256
4.6.1 Some Traditional Measures 256 4.6.2 System Performance Measures 258 4.6.3 Spatial Adaptive Processor 263 4.7 Direction Finding 264 4.8 Array Phase Center 266 4.9 Typical Results 270 4.9.1 Effects of Temporal Taps 271 4.9.2 Effects of Temporal Taps for Different Types of Jammers 271 4.9.3 Effects of Jammer Spacing on Satellite Availability 272 4.9.4 Maximum Number of Jammers to Null 273 4.9.5 Frequency-Agile Jammers and Stale Weights 275 Bibliography 277 Endnotes 278 CHAPTER 5 Ground Plane, Aircraft Fuselage, and Other Platform Effects on GPS Antennas 279 5.1 Introduction 279 5.2 Microstrip Antenna on a Planar Ground Plane 280 5.2.1 Planar Ground Plane Effects 280 5.3 Mitigation of Ground Plane Effects on Performance of GPS Antennas 287 5.3.1 Choke-Ring Ground Plane 288 5.3.2 EBG Ground Plane 288 5.3.3 Rolled Edge Ground Plane 290 5.3.4 Resistivity Tapered Ground Plane 292 5.4 Radiation Patterns of Aircraft Mounted GPS Microstrip Antennas and Verification Through Scale Model Testing 293 5.4.1 Scale Model Investigations on a GPS Antenna on a Beechcraft 1900C Aircraft 295 5.4.2 Validation of the Aircraft Newair Code for Predicting Antenna Patterns of Fuselage-Mounted GPS Patch Antennas 299 5.4.3 Newair Analysis of GPS Antenna on a Boeing 737 Aircraft 302 5.5 Radiation Pattern Analysis of a GPS Antenna on an Automobile 304 5.6 Body Interaction with a Handheld GPS Antenna 307 References 307 CHAPTER 6 Measurement of the Characteristics of GNSS Antennas 309 6.1 Introduction 309 6.2 Radiation Pattern Measurements of GNSS Antennas 312 6.2.1 Near-Field and Far-Field Regions of an Antenna 312 6.2.2 Indoor Far-Field Antenna Test Ranges 314 6.2.3 CATR 316 6.2.4 NF-FF Antenna Test Ranges 317 6.2.5 Radiation Pattern Cuts 323
XII Contents 6.3 Measurement of Axial Ratio of the RHCP GNSS Antenna 325 6.4 Gain Measurement of a GNSS Antenna 327 6.4.1 Two-Antenna Gain Transfer Method 329 6.4.2 Three-Antennas Absolute Gain Measurement Method 333 6.4.3 Near-Field Spherical Scanning Techniques for Measuring Gain 336 6.5 Measurement of the Bandwidth of GNSS Antennas 337 6.6 Measurement of PCO and PCV of GNSS Receiver Antennas 339 6.6.1 Microwave Anechoic Chamber Method of Antenna PCV and PCO Calibration 342 6.6.2 Relative Antenna Calibration by Comparison to a Reference Antenna 344 6.6.3 Absolute Robot-Based Antenna Calibration 346 6.6.4 Comparison of the Three Calibration Techniques for Determining PCO and PCV 348 6.6.5 Automated Absolute Field Calibration of the PCV and PCO of a Satellite Transmit Antenna Using a Robot 350 6.7 Group Delay Variation in GNSS Antennas and Its Measurement 351 6.7.1 Requirements for Group Delay Variation with Frequency 353 6.7.2 Group Delay Variation with Aspect Angle 353 6.7.3 Measurement Techniques for Calibrating Group Delay Variation with Frequency and Aspect Angle 354 References 358 CHAPTER 7 Antennas and Site Considerations for Precise Applications 361 7.1 Introduction 361 7.2 Antenna and Site Dependence 362 7.2.1 Multipath Effects, 363 7.2.2 Monument Effects 366 7.2.3 Ground Plane Effects 368 7.2.4 Radome Effects 371 7.3 Measurements and Ionospheric Modeling 371 7.3.1 Phase Center Measurements 373 7.3.2 Tracking Performance Measurements 374 7.4 Perfect Antenna Pattern and Method of Realization 375 7.4.1 Multipath-Limiting Antennas 375 7.5 PCV 379 7.5.1 Modeling and Measurement Methods of PCV 382 7.6 Group Delay Variation Effects 383 7.7 Methods of Improvement for Antenna Performance 383 7.7.1 Design Stage Improvement for Antenna Performance 384 7.7.2 Manufacturing Stage Improvement for Antenna Performance 384 7.7.3 Field Installation Stage Improvement for Antenna Performance 384 References 384
Contents XIII About the Authors 387 Index 389