Research on EMC Evaluation for Large Diameter Radio Telescope

LIU Qi

(Xinjiang Astronomical Observatory,Chinese Academy of Sciences,Urumqi 830011)

ElectroMagnetic Compatibility(EMC)is an important performance indicator of equipment or system,which is also an important factor to ensure the working efficiency of the system and improve the reliability of the system.For large diameter radio telescope constructing and operating stage,potential electromagnetic interference from the radio service around the site and the internal various types of electrics will affect the quality of certain observations or specific observation types,limiting the overall efficiency of radio astronomical observations.This theis investigated the electromagnetic compatibility evaluation technology for the proposed 110 m diameter fully steerable radio telescope (QTT,Qi Tai radio Telescope)in Xinjiang province,which has an important engineering application value.

Firstly,according to the shortcomings of the existing radio environment measurement methods in radio astronomical field,the key parameters configuration and measurement time calculation methods for signal analyzer were analyzed deeply.We useY-factor method for system gain measuring to calibrate Radio Frequency Interference (RFI)data,and a quasi-real-time radio environment measurement method is proposed.For broadband spectra,this thesis analyzed the characteristics of broadband spectra signal and noise,combined with standard deviation theory,a high precision signal-to-noise separation method based on neighborhood value comparison was proposed to realize signal extracted and counted effectively.Additionally,an automated,high-sensitive radio environment monitoring system was developed for QTT site.System performance testing data indicate that,below 6 GHz,the system gain is greater than 40 dB,system noise figure is less than 2 dB,and the measurement uncertainty is less than 1.49 dB,which is sensitive enough for weak signal detection.According to the data flow of spectrum monitoring,we designed a HDF5(Hierarchical Data Format version 5)data format for data storage,and a measurement and monitor software including a data processing software were developed for spectrum monitoring and data processing effectively.Based on the long-term monitoring RFI data,we evaluated RFI environment of QTT,and analyzed the main interference sources characteristics and their effects on observations as well.

Secondly,we proposed an interference level limit quantified method for feed aperture of large diameter telescope.Then a radio wave propagation model based on QTT site terrain was established by analyzing the advantages and disadvantages of the existing radio wave propagation methods.We used Longley-Rice and Two-Ray models to predict the path loss between the potential interference area and QTT.Combined with the proposed large diameter radio telescope antenna gain quantified method,the interference level limit of the potential interference area at QTT were calculated.Furthermore,we investigated and analyzed the EMC measurement standards,and an EMC evaluation method was established for large diameter radio telescope with interference impacting on observations analyzed,which will be applied to the QTT construction and operation stage ensuring that the system has good electromagnetic compatibility.

Finally,we calculated the EMC design requirements according to the interference level limit of potential interference areas,and the preliminary EMC design scheme for QTT was provided.Additionally,in order to mitigate the RFIs in facilities,we proposed a low cost building shielding approach,which was applied to the existing buildings at QTT site.