Research On Coupling Analysis Method Of Electromagnetic Interference For Radio Telescope Based On Electromagnetic Topology

Radio telescope has a very high sensitivity and a wide range of working frequency.When performing observation tasks,it will not only receive the signals generated by the observation target,but also receive various electromagnetic interference signals inside and outside the site,thus affecting the sensitivity and accuracy of the observation.In view of the complexity of electromagnetic interference coupling in radio telescope system,based on the theory of electromagnetic topology,the electromagnetic interference coupling model of radio telescope system is established.According to the criterion of coupling intensity,the electromagnetic interference path of the radio telescope system is divided into sub-paths with different coupling intensity,and the influence of electromagnetic interference inside and outside the site on radio telescope system is analyzed.Finally,the measurement and suppression methods of electromagnetic interference inside the site are studied.The main work and contribution of this dissertation are as follows:Based on the system composition of radio telescope,the electromagnetic interference sources and coupling paths of radio telescope system are analyzed.According to the statistical characteristics of interference signal and noise signal,the sensitivity of radio astronomical observation under signal interference is deduced,and the relationship between noise temperature and sensitivity is obtained.In order to evaluate the influence of electromagnetic radiation from electronic equipment on radio telescope,considering the antenna side lobe gain of radio telescope and the path loss from equipment to the feed of radio telescope,the interference level thresholds of electromagnetic environment at the site is calculated,and the requirements of interference suppression and protection are proposed.A modeling method of electromagnetic interference coupling based on electromagnetic topology theory is proposed.The model of electromagnetic interference coupling of radio telescope system is established,and the relationship between the interference source and the response of the system is determined.Based on the analysis of the condition that BLT equation is simplified to transfer function,a criterion of coupling intensity is proposed.According to the criterion,the electromagnetic interference path of radio telescope system is divided into strong coupling and weak coupling sub-paths.The transfer function of weak coupling sub-path and the BLT equation of strong coupling sub-path are established.Through the transfer function between sub-paths,all sub-paths are synthesized into the path of the whole system,which simplifies the analysis process and the difficulty of modeling.For the interference of external interference sources on radio telescopes through front-door coupling,a prediction method of electromagnetic interference combined with terrain characteristics is proposed.Taking the communication base station as a typical interference source,the radio wave propagation model at the site is established through the terrain modification of the statistical model of radio wave propagation,and the transfer function from the interference source outside the site to the feed of the radio telescope is obtained.In view of the large terrain fluctuation,a prediction method of electromagnetic interference based on relative terrain is proposed.The terrain elevation data extracted by GIS is transformed into the relative terrain data.Using the fluctuation height of the relative terrain as the criterion,and combining the antenna parameters of the communication base station,the interference power of the communication base station to the radio telescope is calculated.The influence of base station parameters on path loss and interference power is analyzed by using collaborative simulation method based on step-by-step equivalence.The results show that the interference power is greatly affected by the specific terrain.For the back-door coupling interference of electronic equipment in the site,transfer functions of aperture coupling and field-wire coupling are used to describe the propagation and coupling of interference through internal space and cable.By establishing BLT equation and transfer function of aperture coupling model respectively,based on the proposed combined analysis method,the induced currents of transmission line load in the rectangular shield are calculated in two cases.In order to analyze the time-domain response of electromagnetic interference from the results of shielding effectiveness or transfer impedance measurement,a frequency-domain equivalent method based on minimum phase method is proposed.By establishing the theoretical model of the system,the transfer function of the system in frequency domain is derived,and the minimum phase reconstructed from the amplitude-frequency curve is compensated according to the distribution of zero and pole of the transfer function.The compensated transfer function and the interference signal are multiplied in the frequency domain and transformed into the time domain.Finally,the time domain response of the system is obtained.The validity of the method is verified by comparing with the test data.An electromagnetic interference on-site test system for radio telescopes is constructed.Based on the spectral difference algorithm with threshold,the environmental interference signals in the test data are eliminated,and the actual electromagnetic emission characteristics of the equipment are obtained.The interference sources are identified by comparing with the environmental monitoring data.Based on the suppression and protection requirements of interference inside the site,a combined shielding scheme that combines building shielding and key subsystems shielding is proposed.In view of the buildings in the site,the specific parameters of the metal wire mesh used for building shielding are determined by comparing the shielding effectiveness of different metal wire meshes in the focus frequency band.For lighting and monitoring equipment,based on their working principles,potential electromagnetic interference problems are analyzed.Through the electromagnetic compatibility reinforcement design of typical equipment,the electromagnetic interference suppression is realized.