GPS Antennas
locate,c
ommun
icate,accelerate
RF Design Considerations for u-blox GPS Receivers Application Note
Abstract Overview of important antenna and interference issues to beconsideredwhenintegratingu-bloxGPSreceivers.
www.u-blox.com
GPSAntennas-ApplicationNote
Document Information
Title GPSAntennas
Subtitle RFDesignConsiderationsforu-bloxGPSReceivers
Document type ApplicationNote
Document number GPS-X-08014-A1
Document status Released
Thisdocumentandtheuseofanyinformationcontainedtherein,issubjecttotheacceptanceoftheu-bloxtermsandconditions.Theycanbedownloadedfromwww.u-blox.com.u-bloxmakesnowarrantiesbasedontheaccuracyorcompletenessofthecontentsofthisdocumentandreservestherighttomakechangestospecificationsandproductdescriptionsatanytimewithoutnotice.u-bloxreservesallrightstothisdocumentandtheinformationcontainedherein.Reproduction,useordisclosuretothirdpartieswithoutexpresspermissionisstrictlyprohibited.Copyright2009,u-bloxAG.
GPS-X-08014-A1 Page 2 of 40
http://www.u-blox.com/
GPSAntennas-ApplicationNote
Contents
Contents..............................................................................................................................3
1 Introduction..................................................................................................................5
2 Antenna basics .............................................................................................................5 2.1 Generalconsiderations ......................................................................................................................... 5 2.2 Antennarequirements.......................................................................................................................... 5 2.3 Antennaplacement .............................................................................................................................. 6 2.4 Activeandpassiveantennas ................................................................................................................. 7
3 Passive antenna types..................................................................................................8 3.1 Patchantenna ...................................................................................................................................... 8 3.2 Helixantenna ....................................................................................................................................... 9 3.3 Monopoleantennas ........................................................................................................................... 10
3.3.1 Chipantenna .............................................................................................................................. 10 3.3.2 FractalElementAntenna(FEA)..................................................................................................... 13
3.4 Dipoleantenna................................................................................................................................... 14 3.5 Loopantenna ..................................................................................................................................... 15 3.6 PlanarInvertedFAntenna(PIFA) ......................................................................................................... 15 3.7 HighendGPSantennas ...................................................................................................................... 16
4 Which antenna is best for my application? ..............................................................17 4.1 Helixorpatch? ................................................................................................................................... 17 4.2 OtherAntennaTypes.......................................................................................................................... 17
5 Design Considerations ...............................................................................................18 5.1 PatchAntennas .................................................................................................................................. 18
5.1.1 GroundPlane .............................................................................................................................. 18 5.1.2 Placement ................................................................................................................................... 20 5.1.3 ESDIssues ................................................................................................................................... 20
5.2 HelixAntennas ................................................................................................................................... 21 5.2.1 GroundPlane .............................................................................................................................. 21 5.2.2 Placement ................................................................................................................................... 21
5.3 AntennaMatching ............................................................................................................................. 22 5.4 GSMApplications............................................................................................................................... 23
5.4.1 IsolationBetweenGPSandGSMAntenna................................................................................... 23
GPS-X-08014-A1 Released Page 3 of 40
GPSAntennas-ApplicationNote
5.5 DualAntennaSystems........................................................................................................................ 23
6 Interference Issues .....................................................................................................26 6.1 SourcesofNoise................................................................................................................................. 26 6.2 EliminatingDigitalNoiseSources ........................................................................................................ 27
6.2.1 PowerandGroundPlanes ........................................................................................................... 27 6.2.2 HighSpeedSignalLines............................................................................................................... 28 6.2.3 DecouplingCapacitors ................................................................................................................ 28
6.3 Shielding ............................................................................................................................................ 30 6.3.1 FeedthroughCapacitors ............................................................................................................. 30 6.3.2 ShieldingSetsofSub-SystemAssembly ....................................................................................... 32
6.4 IncreasingJammingImmunity............................................................................................................. 33 6.4.1 In-bandjamming......................................................................................................................... 33 6.4.2 Out-bandjamming...................................................................................................................... 33
7 Performance Tests ......................................................................................................35 7.1 Skyview ............................................................................................................................................. 35 7.2 Statisticview....................................................................................................................................... 35 7.3 SupplyVoltageCheck......................................................................................................................... 36 7.4 SensitivityTest .................................................................................................................................... 36 7.5 StartupTest ........................................................................................................................................ 36
Appendix ..........................................................................................................................37
A Example of receiver signal to noise (C/No) performance calculation .....................37
Related Documents ..........................................................................................................39
Revision history................................................................................................................39
Contact..............................................................................................................................40
GPS-X-08014-A1 Released Page 4 of 40
GPSAntennas-ApplicationNote
1 Introduction AntennasareacriticalpartofanyGPSreceiverdesignandtheirimportancecannotbestatedhighlyenough.
Eventhebestreceivercannotbringbackwhathasbeenlostduetoapoorantenna,in-bandjamming,orabadRF-boarddesign.GPSsignalsareextremelyweakandpresentuniquedemandsontheantenna.ThechoiceandimplementationoftheantennacanultimatelyplayasignificantroleinGPSperformance.
ThisdocumentconsiderssomeoftheRFandinterferenceissueswhenimplementingaGPSantenna.
2 Antenna basics 2.1 General considerations AGPS receiverneeds to receive signals fromasmany satellitesaspossible.Optimalperformancewillnotbeavailableinnarrowstreetsandundergroundparkinglotsorifob
