Wideband coaxial cable transfer impedance for Karroo ArrayTelescope

[摘要] ENGLISH ABSTRACT: Through the Karoo Array Telescope, and its extension MeerKAT, South Africa is demonstrating its capabilities to host the most powerful radio telescope ever, the Square Kilometre Array (SKA). This new interferometer is intended to assist radio astronomers in unlocking the mysteries concealed in the far regions of the universe. A thorough investigation of Radio Frequency Interference (RFI) sources at each stage of the design becomes relevant for the success of the project.The electromagnetic coupling through coaxial cables is the main focus of this thesissince 90% of the Electromagnetic Compatibility (EMC) problems come from inadequatesystem layout and grounding, where cabling plays the major role. Interest revolves aroundbetter noise immunity, low radiation and cost. Transfer impedance (ZT ) and shieldinge ectiveness (SE) are used as the cable selection criteria. Several measurements of coaxialcables identi ed on KAT-7 have been performed for ZT characterisation from 300 kHz up to1.3 GHz. A current injection method is used to identify the ZT for the low frequency region.We derived the high frequency part of ZT , with a reverberation chamber technique (RC)measuring shielding e ectiveness. Atrst, we calibrated the RC according to the relevantIEC 61000-4-21 standard and evaluated the result with an Open Area Test Site (OATS)E- eld estimation. The accuracy of the E- eld within the chamber is also addressed, basedon statistical analysis of the chamber's independent samples.The OATS E- eld equivalent determination showed a good correlation with the OATSE- eld data of a standard radiator. A coaxial air-line ZT veri ed the theoretical ZT modelwithin 7 dB and showed the expected 20 dB/decade slope variation. Furthermore, thebraiding porpoising e ect has been noticed with some cable samples. Here, a variation lessthan 20 dB/decade occurs at lower frequency. Then, the slope changes to 20 dB/decadeat high frequency. This study illustrates a practical comparison of cable performance andconstitutes arst approach to RFI mitigation of the MeerKAT cabling system.

[发布机构] Stellenbosch University