PLANAR ANTENNA ARRAYS FOR CORRELATION

104 Pages·2012·7.74 MB·English

The Pennsylvania State University
The Graduate School
College of Engineering
PLANAR ANTENNA ARRAYS FOR CORRELATION
DIRECTION FINDING SYSTEMS FOR USE ON MOBILE
PLATFORMS
A Thesis in
Electrical Engineering
by
Elliot J. Riley
c 2012 Elliot J. Riley
(cid:13)
Submitted in Partial Fulfillment
of the Requirements
for the Degree of
Master of Science
December 2012
The thesis of Elliot J. Riley was reviewed and approved* by the following:
Ram M. Narayanan
Professor of Electrical Engineering
Thesis Advisor
Timothy J. Kane
Professor of Electrical Engineering
Keith A. Lysiak
ARL Mentor
Kultegin Aydin
Professor of Electrical Engineering
Head of the Electrical Engineering Department
* Signatures are on file in the Graduate School
ii
Abstract
Radio direction finding systems estimate the direction-of-arrival of electromag-
netic signals. Direction finding systems have used many different processing algo-
rithms since they were first investigated in the beginning of the 20th century. The
processing algorithm that is used to estimate the direction-of-arrival of signals drives
the choice of antenna or antenna array that must be used with the system. The
antenna or antenna array then directly influences the available performance of the
system. This thesis will focus on two planar antenna array designs for use with
a correlation direction finding algorithm. Correlation direction finding algorithms
require precise array manifold data. Array manifold data are comprised of the in-
dividual complex antenna voltage response patterns of each element in the array.
The voltage response patterns of each antenna element are measured over multiple
azimuths, elevations, frequencies, and polarizations. The known array manifold data
are then used to correlate incoming electromagnetic signals to find an estimate of
the direction-of-arrival. The array manifold must have unique response data for all
azimuths of interest to produce unambiguous correlation results. This thesis inves-
tigates the use of two different mechanisms to produce uniqueness or diversity in
array manifold data. One planar antenna array design utilizes equal spaced antenna
elements with the elements providing different response patterns. The other design
utilizes unequally spaced antenna elements with all the elements providing identical
response patterns. The available performance of both antenna arrays for use with a
correlation direction finding algorithm is presented.
iii
Table of Contents
List of Figures vi
List of Tables viii
Acknowledgements ix
1 Introduction 1
1.1 Direction Finding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Direction Finding Systems for Mobile Platforms . . . . . . . . . . . . 2
1.3 Thesis Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Background 4
2.1 Practical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Brief Historical Development . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Common DF Considerations . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.1 Coordinate Systems . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.2 System Design . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.3 Sources of Error . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 Practical Correlation Direction Finding Method . . . . . . . . . . . . 10
2.4.1 Array Manifold . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4.2 Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4.3 CharacterizationofDFAntennaArraysforCorrelationAlgorithm 13
2.5 Properties of Direction Finding Antenna Arrays for Correlation DF
Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3 Antenna Design and Modeling 23
3.1 Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.1 Size Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.2 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.1.3 Array Manifold Diversity . . . . . . . . . . . . . . . . . . . . . 24
3.2 Equally Spaced Pattern Diverse Array . . . . . . . . . . . . . . . . . 25
3.2.1 Square Spiral Antenna Elements . . . . . . . . . . . . . . . . . 25
3.2.2 Array Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2.3 FEKO Modeling of Square Spiral Array . . . . . . . . . . . . 29
3.3 Unequal Spaced Identical Pattern Array . . . . . . . . . . . . . . . . 38
3.3.1 E Patch Antenna Elements . . . . . . . . . . . . . . . . . . . . 38
3.3.2 Array Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3.3 FEKO Modeling of E Patch Array . . . . . . . . . . . . . . . 40
3.4 Modeling Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4 Antenna Prototyping 49
4.1 Prototype Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.2 Square Spiral Array Prototype . . . . . . . . . . . . . . . . . . . . . . 50
4.3 E Patch Array Prototype . . . . . . . . . . . . . . . . . . . . . . . . . 51
iv
4.4 Prototyping Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 56
5 Antenna Testing 62
5.1 Considerations for Measuring Array Manifolds . . . . . . . . . . . . . 62
5.2 Anechoic Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.2.1 Chamber Properties . . . . . . . . . . . . . . . . . . . . . . . 63
5.2.2 Antenna Positioning System . . . . . . . . . . . . . . . . . . . 66
5.2.3 Measurement System . . . . . . . . . . . . . . . . . . . . . . . 67
5.3 Collecting Array Manifold Data in Anechoic Chamber . . . . . . . . . 71
5.3.1 Prototype Antenna Rotations . . . . . . . . . . . . . . . . . . 71
5.3.2 Mounting Bracket . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.3.3 Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.4 Testing Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.4.1 Square Spiral Prototype Array Testing . . . . . . . . . . . . . 78
5.4.2 E Patch Prototype Array Testing . . . . . . . . . . . . . . . . 81
5.5 Testing Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6 Conclusions 85
A Adding Normally Distributed Noise to an Array Manifold 87
B Spherical to Planar Wavefront Conversion 91
References 95
v
List of Figures
1 Spherical Coordinates. . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Modified Coordinate System for Direction Finding Systems. . . . . . 7
3 Block Diagram of a DF System. . . . . . . . . . . . . . . . . . . . . . 8
4 Array Manifold. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5 1D Voltage Array and 2D Array Manifold. . . . . . . . . . . . . . . . 12
6 Correlation Plot with Strong Peak. . . . . . . . . . . . . . . . . . . . 16
7 Correlation Plot with Ambiguity. . . . . . . . . . . . . . . . . . . . . 16
8 Desired Array Manifold Auto-correlation Example. . . . . . . . . . . 18
9 Ambiguous Array Manifold Auto-correlation Example. . . . . . . . . 18
10 Generic DF Array Layout. . . . . . . . . . . . . . . . . . . . . . . . . 23
11 Reconfigurable Square Spiral. . . . . . . . . . . . . . . . . . . . . . . 26
12 Endfire and Broadside Elements. . . . . . . . . . . . . . . . . . . . . 27
13 Endfire and Broadside Element Patterns. . . . . . . . . . . . . . . . . 27
14 Square Spiral Array Layout. . . . . . . . . . . . . . . . . . . . . . . . 28
15 Square Spiral Array Element Impedances. . . . . . . . . . . . . . . . 34
16 FEKO Simulation Coordinate System. . . . . . . . . . . . . . . . . . 35
17 Transformed FEKO Coordinates into DF Coordinates. . . . . . . . . 35
18 Normalized Complex Patterns of Square Spiral Array Elements. . . . 37
19 Square Spiral Array Manifold Characterization. . . . . . . . . . . . . 37
20 E Patch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
21 E Patch Pattern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
22 E Patch Array Layout. . . . . . . . . . . . . . . . . . . . . . . . . . . 40
23 E Patch Array Element Impedances. . . . . . . . . . . . . . . . . . . 45
24 Normalized Complex Patterns of E Array Elements. . . . . . . . . . . 46
25 E Array Manifold Characterization. . . . . . . . . . . . . . . . . . . . 46
26 Layers of Prototype Antennas. . . . . . . . . . . . . . . . . . . . . . . 49
27 Radome Over All Layers of Antenna Structure. . . . . . . . . . . . . 49
28 Underside of Ground Plane with SMA Connectors. . . . . . . . . . . 49
29 Square Spiral Array Prototype. . . . . . . . . . . . . . . . . . . . . . 51
30 Square Spiral Array Element Impedances. . . . . . . . . . . . . . . . 55
31 E Patch Array Prototype. . . . . . . . . . . . . . . . . . . . . . . . . 56
32 E Patch Array Element Impedances. . . . . . . . . . . . . . . . . . . 60
33 Cross Section of Anechoic Chamber. . . . . . . . . . . . . . . . . . . 64
34 Wavefronts in Anechoic Chamber. . . . . . . . . . . . . . . . . . . . . 65
35 Antenna Positioning System. . . . . . . . . . . . . . . . . . . . . . . . 68
36 Antenna Positioning System Base Features. . . . . . . . . . . . . . . 69
37 Roll Head Positioner on Top of Boom. . . . . . . . . . . . . . . . . . 69
38 Electronic Motions of Antenna Positioner Looking from Transmit An-
tenna. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
39 Data Collection System. . . . . . . . . . . . . . . . . . . . . . . . . . 71
40 Prototype Antenna Array Coordinates Defined. . . . . . . . . . . . . 72
41 Antenna Positioning System Orientation. . . . . . . . . . . . . . . . . 73
42 Azimuthal Rotations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
vi
43 Elevation Rotations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
44 Mounting Bracket with Prototype Antenna. . . . . . . . . . . . . . . 77
45 Normalized Measured Complex Patterns of Square Spiral Array Ele-
ments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
46 Normalized Modeled Complex Patterns of Square Spiral Array Elements. 79
47 Measured and Modeled Square Spiral Array Manifold Characterization. 80
48 Normalized Measured Complex Patterns of E Patch Array Elements. 82
49 Normalized Modeled Complex Patterns of E Patch Array Elements. . 82
50 Measured and Modeled E Patch Array Manifold Characterization. . . 83
51 Spherical to Planar Wavefront Diagram. . . . . . . . . . . . . . . . . 91
vii
List of Tables
1 Square Spiral Array Antenna Positions and Pattern Descriptions. . . 28
2 E Patch Array Antenna Positions and Pattern Descriptions. . . . . . 40
3 Symbols and Descriptions for Spherical to Planar Wavefront Diagram. 92
viii
Acknowledgements
I would like to first thank The Applied Research Laboratory at Penn State for
providing me with an opportunity to work on a research project. I would also like
to thank a few members of Penn State ARL for their continued help. Thank you
Dr. Keith Lysiak for mentoring me in the theory and operation of direction finding
systems and providing guidance in my research. Thank you Dr. Erik Lenzing for
guiding me in hands on laboratory tasks. Thank you Mr. Dan Brown, Mr. Isaac
Gerg, and Mr. Cale Brownstead for the endless help with MATLAB and document
preparation.
I would also like to thank a few academic members of Penn State University.
Thank you Dr. Ram Narayanan for advising my academic and thesis work and for
introducing me to antenna theory and design in an undergraduate course in the fall of
2010. Thank you Dr. Kane for serving on my committee and for sparking my interest
in electromagnetic theory and applications during an undergraduate electromagnetic
course in the spring of 2010.
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1 Introduction
1.1 Direction Finding
The objective of a direction finding system is to estimate the direction-of-arrival
(DOA), angle-of-arrival (AOA), or line-of-bearing (LOB) of a signal. Direction find-
ing may go by the name of radio direction finding (RDF), but in this thesis it will be
simply referred to as direction finding (DF). The DOA, AOA, or LOB estimate may
also be simply referred to as the bearing of the received signal. It should be carefully
noted that by the strictest definition of a DF system that a DF system determines
the DOA of a received signal and does not determine the direction to the transmitter.
However, an estimate of the direction to the transmitter may be what is truly desired
by the system operator. Many factors may alter a signal during its transmission from
the transmitter to the DF system that may cause the DOA estimate to not give the
true great-circle direction to the transmitter.
To give a complete DOA estimate, the system must provide azimuth and ele-
vation angles of the received signal. Azimuth is the angle in the horizontal plane
and elevation is the angle in the vertical plane. An ideal DF system would provide
360◦ of azimuth coverage, 180◦ of elevation coverage, operate over a wide frequency
band, work with all modulations, and work with signals that are of all lengths of
time. Most generally the signals received by DF systems in real applications will be
non-cooperative.
DF systems use carefully designed antennas or antenna arrays to exploit as much
informationaspossiblefromincomingsignalstodetermineaDOAestimate. Different
algorithms and processing systems require different and precise antenna systems. The
algorithmsusedtodeterminetheDOAestimatedrivetheantennasystemdesignwhile
the antenna system design determines the obtainable accuracy of the overall system.
Prior knowledge of the antenna responses is a vital piece to a DF system. Different
1