Investigating EMC policies for the SKA

1
Investigating EMC policies for the SKA

• Paul van der Merwe
• Prof. HC Reader
• Stellenbosch University

2
Introductory background

• What was done during 2009?
• Cable tray measurements
• Pedestal interfaces
• Karoo site visit
• European visit investigating 2-PAD and EMBRACE
  aperture arrays

3
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.

4
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.

5
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
• 
  
  

6
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

Method 1
Method 2
7
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.

8
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.

9
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
10
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

11
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.

12
Transfer impedance measurement

• Transfer impedance
• Identify transfer impedances in EMBRACE grounding
  system.
• Influence of transfer impedance can be
  approximated

13
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.