Interface and cabling characterization for SKA

1. Interface and cabling characterization for SKA Paul van der Merwe Prof. HC Reader Stellenbosch University

2. Introductory background 2007 • Masters program: -Fundamental EMC principles. -RFI mitigation. -Accurate measurements. • Cable trays Enclosures • Verify results screened room measurements using computational analysis. 2008 • PhD continuation cable tray measurements: -End-terminations and mid-span connections. -Plane wave radiation. • Simulation of pedestal base.

3. Model 2 Model 1 Cable tray connections: Visualizing Physics • No clear definition end-terminations and mid-span connections. • Two models, two methods inducing CM currents. • Investigated connections specified standards and EMC literature. • Screened room measurement. • Explained results current and field arguments.

4. Model 2 Model 1 Cable tray connections (cont): Current analysis Model 1 • Indirect current injection. • Concentrated induced CM current. • Separate excitation and victim loops. • Mid- and end-connections major current diversion increased path impedance high coupling. Model 2 • Direct current injection. • Uniform CM current distribution. • Cable tray common conductor. • Small current diversion for connections path impedance constant invariant coupling.

5. Model 2 Model 1 Cable tray connections (cont 2): Field analysis Model 1 • Resultant magnetic field combination primary field and secondary field. • Current flow influence strength of secondary field. • Secondary subtract primary field. • Side straps and L-brackets – high coupling. Wide bottom connection or U-bracket – low coupling. Model 2 • Excitation and victim loop connected via cable tray common conductor. • Interference coupling to victim loop constant regardless of connection type. • Same field intersects victim loop regardless type of end- or mid-connection.

6. Cable tray connections (cont 3): Typical Results Model 1 Model 2

7. Radiation of cable trays: Visualizing the problem • Lower frequency analysis complete, next step HF radiation. • One model used: -Anechoic chamber -OATS • Absorbing anechoic chamber, ground reflections OATS. • LPDA and horn antennas used. • Purpose: Comparison measured data with computed data using plane wave excitation.

8. Radiation of cable trays (cont): Adaptation Bad Luck • Initial measurement procedure using VNA. • VNA calibration. • VNA not performing satisfactorily on day of measurement. • Signal generator and SA. • Uncalibrated system cable loss added in post-processing. Good Luck • Voltage calculated in computation - voltage available from measurements. • Signal generator as transmitter, SA as receiver: voltage into 50 Ω load calculated. • Antenna input power known, compensate S11 mismatch.

9. Radiation of cable trays (cont 2): Compensation OATS influences • OATS has reflective ground plane. • Minimize ground reflection, placing receiver close to ground. • Interference removed by calculating phase change along reflected path. • Computation included ground plane therefore multi-path interference.

10. Next step Why all the previous work? • Want to know: Level of inter-cable coupling in pedestal base. • What to do: Implement measures minimizing external energy entering pedestal. • Constraints: Cost effective and practical.

11. Finally • Best end and mid-span connections using current and field arguments. • HF radiation measurements of cable tray structure. • Anechoic chamber and OATS measurements. • Pedestal and concrete base study. • Best interface.