Transcript Paul S van der Merwe - SKA Presentation Dec 2009

Investigating EMC policies for the
SKA
Paul van der Merwe
Prof. HC Reader
Stellenbosch University
Introductory background
What was done during 2009?
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•
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Cable tray measurements
Pedestal interfaces
Karoo site visit
European visit investigating 2-PAD and EMBRACE
aperture arrays
Cable tray radiation measurements
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Determine the shielding ability of cable trays in high
frequency RFI environments.
Make use of known gain antennas and anechoic
chamber.
S21 measured – induced voltage and gain calculated.
Define two methods using computational analysis.
Shielding analysis of cable trays: Method 1
• The cable tray structure is radiated using a plane wave definition
with known E-field level.
• Voltage induced on victim cable in cable tray measured at port.
Shielding analysis of cable trays: Method 2
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The cable tray structure is excited and far field radiation pattern is measured
Gain computed and compared to calculated gain using measured S21
Comparison: Measurement & Computation
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Comparing measured and computed data validates the accuracy of the
computational model.
Sequence have to be repeated for various positions of receiving antenna
Method 1
Method 2
Plotting the measured and computed values for the cable tray being radiated on a linear scale
-30
Measured voltage radiated at 90 deg
-35
CST voltage radiated at 90 deg
Calculating the gain of the cable tray from measurements using K1 over 6 GHz bandwidth vertically radiated
15
Cable tray gain
CST computed gain
10
-40
5
Gain of cable tray (dB)
Voltage (V)
-45
-50
-55
-60
-65
-5
-10
-15
-70
-20
-75
-80
0
0
1
2
3
Frequency (Hz)
4
5
6
9
x 10
-25
0
1
2
3
Frequency (Hz)
4
5
6
9
x 10
Pedestal interfaces: what can be done?
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Power provision for dish needs to enter pedestal via some cable interface.
CM current on power cable able to enter pedestal.
Bonding of meshed floor to pedestal at point of entry reduces interference.
On-site measurements
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Evaluate site RFI and interference generated by infrastructure.
Radiated interference measured – E-field antenna.
Conducted interference measured – CM current probe.
Proposed measurements on dish cables.
Investigating 2-PAD and EMBRACE: Purpose of visit
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Exchange interaction between South African SKA effort and European
aperture array development.
Become familiar with European SKADS, AAVP setup.
EMI investigations of both 2-PAD and EMBRACE systems.
Improve RFI mitigation for both systems.
Gain knowledge on aperture arrays – measurements experience
2-PAD
EMBRACE
Grounding schematic for array
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Evaluation of induced CM current on system by radiated RFI.
Processing bunker shielding measurements
Transfer impedance measurements of different sections of system
Balun investigation
Power filter connected to
transformer.
Transformer supplies
ground reference
Test Points
A/D
converter
Interface for cables
with 360°
connectors
Non-metallic
sub-frame
F
Ground plane
Antenna elements
PC
I
A
B
Non-metallic
support frame
Capacitive
connection of
ground plane to
ground
EM
Injection
Clamp
Ground
C
Equipotential
bonding conductor
G
D
E
Suggested
grounding points for
chamber
Bunker shielding: How much does it protect?
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Effective shielding of processing bunker important.
Bunker forms major part of RFI mitigation.
Effective diversion of CM current – Measurements conducted.
Validation of effective shielding at interfaces.
EMC
chamber
LPDA
Signal
generator
Current probe
Transfer impedance measurement
Zt 
VDM
I CM
•
Transfer impedance:
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Identify transfer impedances in EMBRACE grounding system.
Influence of transfer impedance can be approximated:
Vx  Z L I DM  Zt ( I DM  I CM )
Antenna
ground plane
ground plane
IConnector
DM
75 Ω
SA
Connector
Antenna
cable
Capacitive
coupling to
ground
Bunker
interface
Signal
sourceAntenna
ICM
EM
injection
clamp
Signal
source
IDM
IDM
ICM
ICM
Circuitry
inside
Bunker
bunker
interface
EM
ZL
injection
clamp
75 Ω
SA
ICM
Ztransfer
cable
ICM
Capacitive Signal
coupling to gen
ground
Ground
ZL
ICM
ZAntenna
transfer
Circuitry
inside
bunker
Vx
Signal
SA
gen
VZt ICM SA
Vx
VZ
t
Finally
• Shielding ability of cable trays at higher frequencies: can they be
used?
• Two methods defined two analyze them.
• Improving the pedestal interfaces for cable entry.
• Initial site evaluation of RFI.
• Investigated 2-PAD and EMBRACE aperture array systems
• Measured the induced CM currents, bunker shielding and transfer
impedance.