Passive Direction Finding Method Of Aircraft And Experimental Study Based On Electromagnetic Radiation Characteristics Of Spark Discharge

With the continuous development of high speed flight technology,many countries,including the United States and Russia,have made some progress in high-speed vehicles,and are still promoting various research and projects of high-speed aircraft and missiles.However,the research on the detection of those aircrafts are still in its infancy,therefore,it is of great significance to study the detection methods of high-speed vehicles.Existing studies have shown that when aircrafts fly through the clouds or at a high speed,discharge process will occur on their surface because of the friction with the atmosphere,and will release electromagnetic waves;which can be received by passive direction finding system to obtain the direction information of the discharge source,in this case,the aircraft.The discharge on aircraft surface includes both weak discharge types such as corona discharge and strong discharge types such as spark discharge.Spark discharge radiates stronger electromagnetic waves compared to corona discharge and is more suitable for passive direction finding.In order to verify the method of passive direction finding by using electromagnetic wave radiated spark discharge on aircraft surface,this paper studies the spark discharge on aircraft surface and the approach to using the radiated discharge signal in passive direction finding system to obtain the direction information of an aircraft.The main achievements of this paper includes:1.The equivalent experimental platform of aircraft surface spark discharge is established,and the radiation characteristics of electromagnetic wave from aircraft surface spark discharge are studied.Experimental results show that the radiated spark discharge signal is an ultra-wideband signal,its energy is mainly distributed in 0 ? 200 MHz,and there are obvious peaks in the three frequency bands of 0 ? 50 MHz,50 ? 100 MHz,and 100 ?200MHz.By changing the experimental conditions,the radiation results under different discharge voltages,electrodes and storage capacitances are obtained.2.The existing model of discharge radiation can only simulate one certain stage of an entire discharge process,so a combined dipole-loop antenna model is proposed.The proposed model can successfully equivalent the whole radiation process of spark discharge on the aircraft surface.The simulation results of proposed model under different conditions are consistent with the experimental results,and the reason of radiation intensity changing under different conditions is analyzed by antenna theory.Conclusion can be drawn that,the equivalent model of dipole ring antenna can simulate the whole radiation process of spark discharge,and provide theoretical basis and basis for the future research.3.Based on the radiation characteristics of spark discharge signal,a multiple baseline wideband time domain interferometry direction finding method using Hilbert transform is proposed.Interferometry has been used in lightning location for a long time,and has many advantages in the direction finding of discharge signal.However,the discharge radiation signal on the aircraft is weaker than lightning radiation signal,and it has lower signal-tonoise ratio.If it is superimposed with its inherent high-frequency oscillation characteristics,it will cause the wrong peak value in the correlation calculation and affect the direction estimation results.Therefore,Hilbert transform is introduced to improve the performance of traditional interferometry direction finding.Simulation and experimental results show that,compared with the traditional interferometry direction finding method,the proposed method has better estimation performance in low SNR environment.4.Based on the combined dipole-loop antenna model of spark discharge,a combined time-domain antenna is designed to receive the radiated signals from spark discharge.The combined time-domain antenna consists of main structure,low frequency compensation circuit and additional metal strip:(1)The main structure is designed with the reference to exponential tapered TEM horn antenna,which can be equivalent to dipole antenna,and provide ultra-wideband bandwidth for the combined time-domain antenna;(2)The low frequency compensation circuit is composed of three metal plates connected with two horn bodies,which is equivalent to a loop antenna during receiving and to improve the receiving performance of the combined time-domain antenna in the low frequency band;(3)A small metal strip is connected with other antenna bodies to form another loop antenna.It is to further reduce the lower limit of the effective frequency band of the combined antenna without increasing the antenna size.The simulation results show that the combined timedomain antenna has ultra-wideband characteristics,and its receiving performance meets the requirements in the lower frequency band.5.An equivalent experiment platform is established to verify the passive direction finding method of aircraft based on spark discharge radiation characteristics proposed in this dissertation.In the experiment,the spark discharge circuit is used as the discharge source of aircraft surface spark discharge,the combined time-domain antenna is used as the receiving antenna array element,and the proposed Hilbert transform multiple baseline wideband timedomain interferometry method is used for the angle estimation.The experimental results under different conditions show that the proposed method can effectively use the spark discharge signal on the surface of the aircraft to obtain the two-dimensional direction angle of the aircraft.According to the research work in this dissertation,firstly,the radiation characteristics of spark discharge on aircraft surface are obtained,and a combined dipole-loop antenna model which can effectively simulate the radiation process of spark discharge is established.Based on the ultra-wideband characteristics of discharge radiation signal,a multiple baseline wideband time domain interferometer direction finding method using Hilbert transform is proposed.Based on the combined dipole-loop antenna model of spark discharge,a combined time-domain antenna for receiving spark discharge radiation signal is designed.Finally,an equivalent experiment is carried out using spark discharge source,combined time-domain antenna and the proposed direction finding method,and the experimental results are analyzed.The research results of this dissertation preliminarily verify the feasibility of passive direction finding using discharge radiation signal from the aircraft surface.