Beamforming and timing design issues for a large aperture array radar applied to atmospheric ...

158 Pages·2009·13.25 MB·English

by  Gustav Johansson

ISSN: 1402-1544 ISBN 978-91-86233-XX-X Se i listan och fyll i siffror där kryssen är
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Beamforming and Timing Design
Issues for a Large Aperture Array
Radar Applied to Atmospheric
Research
Gustav Johansson
Dept. of Computer Science and Electrical Engineering
Lule˚a University of Technology
Lule˚a, Sweden
Supervisors:
Prof. Jerker Delsing
Dr. Jonny Johansson
Printed by Universitetstryckeriet, Luleå 2009
ISSN: 1402-1544
ISBN 978-91-86233-74-7
Luleå 2009
www.ltu.se
To Mini, Isaac and Lucas.
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Abstract
This thesis describes the work done by the author during the development of a Large
ApertureArrayRadar(LAAR)receiverfortheEISCAT 3Dproject. Themainfocuswas
on digital beamforming of a bandpass-sampled wide band signal in base-band and the
developmentofapicosecond-leveldistributedtimingsystemapplicableoverhundredsof
meters.
The next generation of atmospheric research radars all have the common goal of
increasingtheircapabilitieswithimprovedversatilityanddynamicobservationcapability.
Pastradarshavemostlybeencapableonlyofobservingasinglevolumeoftheatmosphere
at one time, thereby limiting scientists to looking only at small-scale phenomena in the
ionosphere. Byallowingsimultaneousobservationofmultiplevolumeswithahighlevelof
accuracy, EISCAT 3D will give scientists a new tool for improving our knowledge about
Earth’s atmosphere.
To provide instantaneous coverage of multiple volumes of the ionosphere, it is neces-
sarytohaveamultiplebeamreceiver. Thegoaloftheantennadesigninthisprojectwas
tocreatedigitallysteeredarraysthatwillprovideeasyscalability,suchasincreasingthe
numberofbeams,afterthearrayshavebeenbuilt,andmakethestringenttargetsofthe
radar’s capabilities achievable.
Thisthesisisdividedintointroductorychaptersandfiveattachedpapers. Theintro-
ductorychaptersdescribethebackgroundandsomeofthereasonsbehindatmosphericre-
search,IncoherentScatterRadar(ISR)technologyanduse,andtheEISCAT 3Dproject,
specifically, the technological challenges encountered on the LAAR receiver. The tech-
nologies evaluated and implemented in the test array for the EISCAT 3D project are
detailed, and the results and conclusions are discussed.
The technological investigation showed that digital beamforming and high accuracy
timing are critical issues for the EISCAT 3D LAAR. Digital beamforming is necessary
primarilyduetothelargearraysizeandstringentdemandsonpointingaccuracy, which
rendertheuseofanalogbeamformingimpracticalatbest. Theinter-elementtimingerror
inthearrayisshowntohaveamaximumstandarddeviationof120ps. Thisrequirement
issetonanarraywherethedistancebetweentwoelementscanbeinthekilometerrange.
Twodifferentsolutionscapableofachievingatimingerroroflessthan25psaredetailed,
as well as digital beamforming filters that have a maximum error of less than 5 ps. In
conclusion, it is shown to be possible to build the EISCAT 3D LAAR with technology
that exists today.
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Contents
Part I xiii
Chapter 1 – Thesis Introduction 1
Chapter 2 – Atmospheric Research 5
2.1 Stratospheric Balloon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Sounding Rocket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Incoherent Scatter Radar . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.4 MST-Radar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.5 Satellite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Chapter 3 – Incoherent Scatter Radar 9
3.1 The Ionosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 Incoherent Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3 Currently Active ISRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4 Developing ISRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Chapter 4 – EISCAT 3D 17
4.1 Resolution and Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.2 Large Aperture Array Radar . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.3 Sampling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Chapter 5 – Digital Beamforming 23
5.1 Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.2 Filter Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.3 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Chapter 6 – Timing and Calibration 27
6.1 Timing Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.2 Calibration Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.3 Statistical Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Chapter 7 – Summary of the Papers 35
7.1 Paper A - Simulation of Post-ADC Digital Beamforming for Large Aper-
ture Array Radars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.2 PaperB-APicosecondAccuracyTimingSystemBasedonL1-onlyGNSS
Receivers for a Large Aperture Array Radar . . . . . . . . . . . . . . . . 36
7.3 Paper C - Picosecond Level Error Detection using PCA in the Hardware
Timing Systems for the EISCAT 3D LAAR . . . . . . . . . . . . . . . . 36
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7.4 PaperD-ProposalforaPicosecondLevelCable-BasedCalibrationSystem
for Large Aperture Array Radars . . . . . . . . . . . . . . . . . . . . . . 37
7.5 Paper E - EISCAT 3D - a Next-Generation European Radar System for
Upper Atmosphere and Geospace Research . . . . . . . . . . . . . . . . . 38
Chapter 8 – Conclusions 41
References 43
Part II 47
Paper A 49
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2 Design Choices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3 Fractional Sample Delay Beam-Steering. . . . . . . . . . . . . . . . . . . 56
4 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Paper B 69
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2 Timing System Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3 GNSS Simplified Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4 Test Setup for Concept Evalution . . . . . . . . . . . . . . . . . . . . . . 76
5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Paper C 81
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
2 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Paper D 95
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
2 Calibration System Design . . . . . . . . . . . . . . . . . . . . . . . . . . 99
3 Calibration System Implementation . . . . . . . . . . . . . . . . . . . . . 102
4 Calibration Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
6 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Paper E 117
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
2 EISCAT 3D Performance Targets . . . . . . . . . . . . . . . . . . . . . . 120
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