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Download Paul S van der Merwe - SKA Presentation Dec 2009
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Transcript
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 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? • • • 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 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? • • • • 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: • • 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.