GPS World, February 2009

INNOVATION Antenna Technology Conclusion In this article we have presented an overview of the most important characteristics of GNSS antennas Several GNSS receiver antenna classes were discussed based on their typical characteristics and the resulting specification compromises were outlined Hopefully this information will help you select the right antenna for your next GNSS application Acknowledgment An earlier version of this article entitled Basics of GPS Antennas appeared in The RF Microwave Solutions Update an online publication of RF Globalnet www rfglobalnet com GERALD J K MOERNAUT holds an M Sc degree in electrical engineering He is a full time antenna design engineer with Orban Microwave Products a company that designs and produces RF and microwave subsystems and antennas with offices in Leuven Belgium and El Paso Texas DANIEL ORBAN is president and founder of Orban Microwave Products In addition to managing the company he has been designing antennas for a number of years Geodetic Rover Handheld versus azimuth should be low because the orientation of the antenna with respect to magnetic north say is usually unknown and cannot be corrected for in the receiver A rover antenna is typically mounted on a handheld pole Good front to back ratio is required to avoid operator reflection multipath and ground noise pickup Yet these rover type applications are high accuracy and require a good phase center stability However since a choke ring cannot be used because of its size and weight a higher phase center variation compared to that of a geodetic antenna is typically inherent to the rover antenna design A good AR and a decent gain roll off at low elevation angles ensures good multipath suppression as heavy choke rings are not an option for this configuration Handheld Receiver Antennas These antennas are singleband L1 structures optimized for size and cost They are available in a range of implementations such as surface mount ceramic chip helical and patch antenna types Their radiation patterns are quasi hemispherical AR and phase center performance are a compromise because of their small size Frequency bands Single to multiband Broadband Single to multiband Narrow to broadband Single band Narrow band Gain pattern Controlled Controlled Not controlled Multipath suppression High Medium None Sensitivity High Medium to high Low Interference handling High rejection Good rejection Minimal rejection Phase center Very important Important Not important Dimensions Large Portable Very small Weight Heavy Portable Lightweight Cost High Medium Low Because of their reduced size these antennas tend to have a negative gain of about 3 dBi 3 dB less than an ideal isotropic antenna at boresight This negative gain is mostly masked by an embedded LNA The associated elevated noise figure is typically not an issue in handheld applications Summary of Antenna Types TABLE 2 presents a comparison of the most important properties of geodetic rover and handheld types of GNSS antennas FURTHER READING Previous GPS World Articles on GNSS Antennas Getting into Pockets and Purses Antenna Counters Sensitivity Loss in Consumer Devices by B Hurte and O Leisten in GPS World Vol 16 No 11 November 2005 pp 34 38 Characterizing the Behavior of Geodetic GPS Antennas by B R Schupler and T A Clark in GPS World Vol 12 No 2 February 2001 pp 48 55 A Primer on GPS Antennas by R B Langley in GPS World Vol 9 No 7 July 1998 pp 50 54 How Different Antennas Affect the GPS Observable by B R Schupler and T A Clark in GPS World Vol 2 No 10 November 1991 pp 32 36 Å TABLE 2 Characteristics of different GNSS antenna classes Introduction to Antennas and Receiver Noise GNSS Antennas and Front Ends in A Software Defined GPS and Galileo Receiver A Single Frequency Approach by K Borre D M Akos N Bertelsen P Rinder and S H Jensen Birkhäuser Boston Cambridge Massachusetts 2007 The Technicians Radio Receiver Handbook Wireless and Telecommunication Technology by J J Carr Newnes Press Woburn Massachusetts 2000 GPS Receiver System Noise by R B Langley in GPS World Vol 8 No 6 June 1997 pp 40 45 More on GNSS Antenna Types The Basics of Patch Antennas by D Orban and G J K Moernaut Available on the Orban Microwave Products web site http www orbanmicrowave com The_ Basics_ Of_ Patch_ Antennas pdf Project Examples http www orbanmicrowave com project htm Interference in GNSS Receivers Interference Heads Up Receiver Techniques for Detecting and Characterizing RFI by P W Ward in GPS World Vol 19 No 6 June 2008 pp 64 73 Jamming GPS Susceptibility of Some Civil GPS Receivers by B Forssell and T B Olsen in GPS World Vol 14 No 1 January 2003 pp 54 58 GPS World February 2009 www gpsworld com 48