the ska aa-lo array; e.m. simulation and design
DESCRIPTION
The SKA AA-lo array; E.M. simulation and design. Eloy de Lera Acedo (UCAM) Nima Razavi-Ghods (UCAM) David Gonzalez-Ovejero (UCL) Luis Enrique Garcia (UC3M) Christophe Craeye (UCL) Peter J. Duffett-Smith (UCAM) Paul Alexander (UCAM). Overview. Towards the SKA: The SKA-AAlo - PowerPoint PPT PresentationTRANSCRIPT
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Widefield Astronomy and Technologies for the SKA4 - 6 November 2009 at Limelette, Belgium
The SKA AA-lo array; E.M. simulation and design
Eloy de Lera Acedo (UCAM)
Nima Razavi-Ghods (UCAM)David Gonzalez-Ovejero (UCL)Luis Enrique Garcia (UC3M)Christophe Craeye (UCL)Peter J. Duffett-Smith (UCAM)Paul Alexander (UCAM)
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Overview
Towards the SKA: The SKA-AAlo The BLU antenna The BLU antenna in a regular array Simulating large random finite arrays… Numerical results Current state specifications Future work Conclusions
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Towards the SKA: The SKA-AAlo It is part of Prep-SKA. Frequency range from 70 MHz to 450 MHz and +/- 45o scan range:
Irregular vs Regular / Dense vs Sparse (Memo 87). Sky noise limited? At 100 MHz: 4000 m2/K. Up to at least 10000 elements per station. For more specifications: Memo 111 (R. Bolton et al).
100 200 300 400 45070 MHz10
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Overview
Towards the SKA: The SKA-AAlo The BLU antenna The BLU antenna in a regular array Simulating large random finite arrays… Numerical results Current state specifications Future work Conclusions
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The BLU antenna Bow-tie Low-frequency Ultra-wideband antenna. Low profile and differential feeding. Wide beam width. Good matching at the high end of the band where the sky
noise does not limit the performance. Small and cheap.
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Overview
Towards the SKA: The SKA-AAlo The BLU antenna The BLU antenna in a regular array Simulating large random finite arrays… Numerical results Current state specifications Future work Conclusions
![Page 7: The SKA AA-lo array; E.M. simulation and design](https://reader034.vdocuments.mx/reader034/viewer/2022042704/56814a4a550346895db7677c/html5/thumbnails/7.jpg)
The BLU antenna in a regular array Infinite array simulations were carried out to analyze the sensitivity
of a unit cell containing a BLU antenna versus the inter-element spacing, the antenna size and the tilt angle of the arms.
+ Info
- GND @ λ/4 @ the highest freq. - No dielectric.
L
L
Z = 200Ω Z = 200Ω
d
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The BLU antenna in a regular array The sky will dominate a large part of the band. Furthermore,
grating lobes will show up in the band.
+ Info
- Sky noise- Receiver noise- System noise
)())(1()()(
)(40000
0
2
rTTrrTr
rGS
LNAambradskyrad
cell
Table 1: Idealize LNA parameters.
875.4691.1)( 751.2 ffT
Fmin Rn Zopt Zamp
0.2 10 Ω 200 Ω 200 Ω
Physical size of the unit cell
)())(1()()(
)(40000
0
2
rTTrrTr
rGS
LNAambradskyrad
cell
Table 1: Idealize LNA parameters.
875.4691.1)( 751.2 ffT
Fmin Rn Zopt Zamp
0.2 10 Ω 200 Ω 200 Ω
System noise
Receiver noise
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The BLU antenna in a regular array In the infinite array the sensitivity of a unit cell in the regular
array improves as sparser is the array in the dense regime while it saturates for the sparse regime. The transition band is the key.
Sensitivity
for different Inter-element
spacing distances d L
λ/2 @:
70-300MHz
Fixed to λ/2 @
300MHz
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The BLU antenna in a regular array Larger antennas bring a multi-lobulation issue at high
frequencies.
Sensitivity
for different antenna sizes.
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The BLU antenna in a regular array An optimum tilt angle can be found for the antenna arms. The
impedance match improves and so does the receiver noise. This is of special interest for the region in between the dense and sparse regions.
Trec
for different antenna angles
α
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Overview Towards the SKA: The SKA-AAlo The BLU antenna The BLU antenna in a regular array Simulating large random finite
arrays… Numerical results Current state specifications Future work Conclusions
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Simulating large random finite arrays…
Based on Method of Moments + MBFs (CBFs) and the interpolation technique presented in [1], where the computation of interactions between MBFs is carried out by interpolating exact data obtained on a simple grid.
[1] D. Gonzalez-Ovejero and C. Craeye, “Fast computation of Macro Basis Functions interactions in non-uniform arrays,” in Proc. IEEE AP-S Soc. Int. Symp., San Diego, CA, Jul. 2008.
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Simulating large random finite arrays…
A so-called “radius of
influence” is defined for
every antenna in the array.
The interactions between MBFs are computed
only within that region reducing drastically the
number of unknowns.
The system is solved within each region of influence for
each antenna.
30λ
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Overview
Towards the SKA: The SKA-AAlo The BLU antenna The BLU antenna in a regular array Simulating large random finite arrays… Numerical results Current state specifications Future work Conclusions
![Page 16: The SKA AA-lo array; E.M. simulation and design](https://reader034.vdocuments.mx/reader034/viewer/2022042704/56814a4a550346895db7677c/html5/thumbnails/16.jpg)
Numerical results
- Distance to ground plane = λ0/4. - No dielectric.
- Array radius = 30λ0. - Number of elements = 1000. - Minimum average separation = 1.5λ0.
λ0
λ0
Z = 200Ω
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Numerical results
λ = 3λ0
2max____
2max____10log10 radiusvpolvpolradiushpolhpol patternpatternabspatternpatternabserr
*Embedded Element Pattern
for radius of influence = 10λ
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Numerical results
EEP- SEP = 0.379 dB in broadsideEEP- SEP = 0.2 dB in broadside
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Numerical results
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Current state specificationsFor previous simulation: Computation time:
Preprocess (computing data to interpolate): 37 min Computing 1000 EEP: 1000•36 s ~ 10h.
Memory: Only 17.8 MB of contiguous memory required.
Speed 10h per simulation: excessive. Sparse matrices (initial results):
Simulation time reduced to 1h. Requires more contiguous memory: 1.77 GB
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Future work Full EM simulation of a real size SKA station. Optimization:
Use of different NFFT (Non-uniform Fast Fourier Transform) schemes for the array pattern calculation.
Paralelization of the code in a cluster of computers. Full migration to C code. Use of sparse matrices solvers.
Validation of the code with a scaled prototype of an SKA AA-lo station.
Analysis of the mutual coupling effects in irregular arrays (random sparse vs dense regular ?). Station+antenna design.
Work towards the telescope calibration…
- Scaled and small SKA AA-lo station.
- 400 elements.
- Scale: 30:1 of the BLU antenna.
- 1m2.
- UWB baluns.
- Band: 2.1 GHz to 13.5 GHz.
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Conclusions MoM/MBF based method to simulate large
finite irregular arrays. Objective: Full fast EM characterization of a
SKA station. Analysis and design (randomness, sparseness, etc.). Can we help?
Analysis of an infinite regular array of BLU antennas proving its suitability for the SKA AAlo.