Reverberation chamber time and frequency metrology for MeerKAT systems shielding evaluation

[摘要] ENGLISH ABSTRACT: Electromagnetic shielding plays a significant role in the protection of electronic equipment.Its application is essential for mitigating radio-frequency interference for the Karoo ArrayTelescope (MeerKAT) project in the Karoo region of the Northern Cape. In this context,time-domain (TD) methodology for small enclosure shielding effectiveness (SE) is developedusing a reverberated environment technique. Interest revolves around measurement timespeed-up and an extended SE response which covers the under-moded condition of smallenclosures. Recommended IEC standard 61000-4-21 [1] e ciency of 0.75, for log-periodicdipole array (LPDA) antenna, is also validated from a reverberation chamber (RC)characterisation of a printed circuit-board (PCB) LPDA e ciency.A built-in pulse generator and the Square Kilometre Array (SKA) receiver RATTY formthe main elements of the TD metrology. For validation purpose, a reference coaxial airlineis built. The cable is characterised with computational codes (CST and FEKO) and isalso modelled with Vance and Kley's analytical expressions. The results are comparedwith TD transfer impedance (Zt) measurement within the RC. The study shows that thecablefixture within an RC shapes the cable under-test (CUT) Zt. The airline itself isalso introducing an oscillating component within Zt. The resonance is proportional to theCUT length and it is visible within the measurement data and the simulations. It is not,however, taken into account by the theoretical models.The consequence of an incorrect antenna efficiency on RC applications is also addressedusing a PCB LPDA antenna efficiency investigation. The unknown LPDA is simulatedwith CST for the study. The result is compared to an RC measurement validating the IEC61000-4-21 standard efficiency recommendation of 0.75 [1]. This methodology characterisedthe unknown antenna parameter from a reference dipole antenna efficiency we investigatedwith FEKO. Simulated Wheeler-cap techniques permitted the reference antenna validation.We found that an inaccurate LPDA efficiency has little effect at higher frequency if theIEC efficiency is adopted. However, a difference of more than 7 dB can arise at lowfrequency if the real efficiency differs by more than 0.3 with respect to the IEC value.The study highlights the importance of a correct antenna efficiency for accurate RCapplications.The nested-enclosure technique is regarded as the conventional method of investigatingsmall enclosures SE [2]. The technique is in general time-consuming and works for a frequency range higher than three times the enclosure under test (EUT) lowest cut-o value. Our TD metrology covers a frequency band up to 1.4 GHz which coincides withour enclosure under-moded region. The SE characterisation is not well-documentedwithin this particular region. The dissertation contributes to thisfield using a non-stirrednested-enclosure configuration. In contrast to the conventional use of the nested-enclosuremethodology [2], the source is placed here within the EUT and the enclosure is treated asa normal radiator. The SE definition according to the IEEE standard in [2] is followedand the enclosure total transferred-power is computed from the port's reflection coeficient.The approach does not require a stirrer for the EUT. Our measurement shows an SEagreement between the modfied and the appropriate nested-enclosure technique from 390MHz up to 4 GHz. The investigation is faster, but in addition the TD spectrum gives amore detailed SE response than the FD approach.

[发布机构] Stellenbosch University