A Picosecond Accuracy Timing System Based on L1-only GNSS Receivers for a Large Aperture Array Radar

Gustav Stenberg, Tore Lindgren, Jonny Johansson

Abstract:	This paper describes a method for, and test results of, a GNSS-based high accuracy timing system formed with L1- only GNSS application specific receivers in combination with an FPGA. The results are used as a proof of concept to meet the demand for a highly accurate timing system to by used in the EISCAT 3D project. EISCAT 3D is a Large Aperture Array Radar, with direct sampling at each antenna element and constituted of up to 16.000 antenna elements, intended for atmospheric research. The requirement of the timing system is rigid: a standard deviation of no more than 50 ps is allowed on the timing between any antenna elements in the array. Such accuracy is improbable to achieve with the traditionally often used non-calibrated cable-based clock distribution system since even heating of the clock distribution cables can alter the length of the cables to the extent that too large errors are generated. A GNSS-based clock distribution system is unaffected by such effects. Other benefits of building a GNSS timing system include lower cost due to reduced amount of coaxial cable throughout the array. Also, there will be no need to build a continuous cable length calibration system that ensures timing accuracy of the distributed clock system to the necessary levels. Test results show that even without integration, a total clock distribution jitter of approximately 50 ps is achievable with simple calculations that can be implemented into an FPGA.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	576 - 580
Cite this article:	Stenberg, Gustav, Lindgren, Tore, Johansson, Jonny, "A Picosecond Accuracy Timing System Based on L1-only GNSS Receivers for a Large Aperture Array Radar," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 576-580.
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