Transcript Numerical Modeling of Antenna Systems for the Square Kilometre Array (SKA)

Numerical Modeling of Antenna Systems for
the Square Kilometre Array (SKA)
NETHERLANDS FOUNDATION FOR RESEARCH IN ASTRONOMY
Rob Maaskant
[email protected]
The LOFAR High Band Antenna
In collaboration with:
- Eindhoven University of Technology (Prof. Anton Tijhuis)
- Penn State University (Prof. Raj Mittra)
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The array modeling problem
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Any wideband densely packed array has significant mutual coupling
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Coupling is a positive thing (gives you bandwidth) but it should be properly taken into
account
– Mutual interaction between elements
– Array truncation effects
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Under some conditions, for example in large aperture arrays, this can be simplified.
However dense FPA’s do not allow these simplifications.
We need a full model for the array receiving system
Modeling of large antenna arrays
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ASTRON concentrates on three activities to address the problem:
1.
Efficient methods
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Use the periodic nature of the structure to speed up computation
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Suitable for design
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In-house software development in collaboration with Eindhoven and
Penn State University
2.
Brute force
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Use the massive power of supercomputers (LOFAR BlueGene/L)
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Application: final simulations and validation
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Penn State (GEMS)
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University of Manchester (FDTD)
3.
System simulation
CAESAR 2.0
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(Computationally Advanced and Efficient Simulator for ARrays)
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Efficient ElectroMagnetic (EM) Solver for Large Antenna Arrays
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MicroWave (MW) circuit simulator for signal and noise analysis
The CAESAR software has been tailored to analyze receiver sensitivities of large
antenna arrays efficiently
Technical report + Getting Started written (124 pages)
Solving antenna array problems using CBFM
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4557 unknowns
(RWGs)
Solving antenna array problems using CBFM
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4557 unknowns
(RWGs)
Allocation of
3 Generating
Sub-Arrays
Solving antenna array problems using CBFM
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2
3
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4557 unknowns
(RWGs)
1
1/2
Apply
Windowing
Technique
Primary CBFs:
2 CBFs
3 CBFs
2 CBFs
Solving antenna array problems using CBFM
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NETHERLANDS FOUNDATION FOR RESEARCH IN ASTRONOMY
4557 unknowns
(RWGs)
Use MoM to
Determine
CBF
Expansion
Coefficients
2
3
3
3
3
3
2
=
19 unknowns
(primary CBFs)
Results for disconnected arrays (LOFAR HBA)
• IE3D
• CBFM
: 8186 unknowns, 2665 sec. (Brute Force)
: 8160 unknowns, 180 sec. (All in MATLAB)
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We gain a speed advantage of 15 times without compromising the accuracy
Results for disconnected arrays (LOFAR HBA)
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Mutual impedance Z1x between the corner and other array elements
Results for disconnected arrays (cont.)
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CAESAR 2.0 : A 20x20x2 array of Bow-Tie elements
• Using translation symmetry, only 761 moment sub-matrix
blocks had to be constructed instead of all 400*400 submatrices
• Initial number of unknowns: 47200 RWGs
• Total simulation time: 24 min. and 45 sec.
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Results for connected single-polarized arrays
 5
Edge truncation effects
# RWGs
# CBFs
Meshing time
CBF Generation time
Matrix Construction Time
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=
93924
1080
40 sec.
4 min. 43 sec.
17 min. 46 sec.
Total CPU time
= 26 min. 41 sec.
(including pattern calculations)
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Combining electromagnetic models
with microwave circuits models
System Modeling
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High S/N
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Study of the noise coupling mechanism
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R. Maaskant, B. Woestenburg, “Applying the Active Antenna
Impedance to Achieve Noise Match in Receiving Array Antennas”,
IEEE AP-S International Symposium, Honolulu, Hawaii, June 2007.
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Combining antenna EM-models with MW-circuit models
Prototype Array
HFSS
CBFM + Feed Model
=
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M.V. Ivashina, E. A. Redkina and R. Maaskant, “An Accurate Model of
a Wide-Band Microstrip Feed for Slot Antenna Arrays”, IEEE AP-S
International Symposium, Honolulu, Hawaii, June 2007.
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In progress: validation for small and very large arrays
In progress: modeling of a 8x7x2 Vivaldi Array
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Measurements
Simulations
114.667 unknowns
reduced to
2968 unknowns
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In progress: a multi-scale antenna problem — arrays of subarrays
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Number of RWGs
Number of CBFs
Meshing Time
Total Solve Time
: 375192
: 4320
: 40 min.
: 5hr. 50 min. (Single CPU 1.73 GHz, 2.0 GB RAM)
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Summarizing
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The CAESAR software is being developed to analyze the receiver sensitivity of
large antenna array systems
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Multi-scale antenna problems are solved using State of the Art modeling techniques
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More research is needed to deal with increasingly larger and complex problems
(computational efficiency, accuracy, robustness, etc.)