Investigating EMC policies for the SKA Paul van der Merwe Prof. HC Reader Stellenbosch University.
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Transcript of Investigating EMC policies for the SKA Paul van der Merwe Prof. HC Reader Stellenbosch University.
Investigating EMC policies for the SKA
Paul van der Merwe
Prof. HC Reader
Stellenbosch University
Introductory background
What was done during 2009?
• Cable tray measurements• Pedestal interfaces• Karoo site visit• European visit investigating 2-PAD and EMBRACE
aperture arrays
Cable tray radiation measurements
• 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
• 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
• Comparing measured and computed data validates the accuracy of the computational model.
• Sequence have to be repeated for various positions of receiving antenna
0 1 2 3 4 5 6
x 109
-80
-75
-70
-65
-60
-55
-50
-45
-40
-35
-30
Vol
tage
(V
)
Frequency (Hz)
Plotting the measured and computed values for the cable tray being radiated on a linear scale
Measured voltage radiated at 90 deg
CST voltage radiated at 90 deg
0 1 2 3 4 5 6
x 109
-25
-20
-15
-10
-5
0
5
10
15
Gai
n of
cab
le t
ray
(dB
)
Frequency (Hz)
Calculating the gain of the cable tray from measurements using K1 over 6 GHz bandwidth vertically radiated
Cable tray gain
CST computed gain
Method 1 Method 2
Pedestal interfaces: what can be done?
• 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
• 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
• 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
• Evaluation of induced CM current on system by radiated RFI.• Processing bunker shielding measurements• Transfer impedance measurements of different sections of system• Balun investigation
Interface for cables
with 360° connectors
Ground plane
Power filter connected to transformer.
Transformer supplies ground reference
Antenna elements
Non-metallic support frame Suggested
grounding points for chamber
Non-metallic sub-frame
Capacitive connection of
ground plane to ground
GroundEquipotential bonding conductor
A
B C
I
D
A/D converter
Test Points
F
EG
PC
EM Injection Clamp
Bunker shielding: How much does it protect?
• 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.
LPDASignal
generator
EMC chamber
Current probe
Transfer impedance measurement
• Transfer impedance:
• Identify transfer impedances in EMBRACE grounding system.
• Influence of transfer impedance can be approximated:
Antenna ground plane
Signal source
Antenna cable
Capacitive coupling to ground
IDM75 Ω SA
SA
ICM
EM injection clamp
Signal gen
ICM
Connector
CM
DMtI
VZ
)( CMDMtDMLx IIZIZV
ICM
Vx VZt
ZL
Circuitry inside bunker
Ztransfer
ICM
Bunker interface
75 ΩSA
EM injection clamp
Signal gen
SA
ICM
IDM
Ground
Vx VZt
ZL
Circuitry inside bunker
Ztransfer
ICM
IDM
ICM
Bunker interface
Antenna ground plane
Signal source
Antenna cable
Capacitive coupling to ground
Connector
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.