Study On Passive Direction Finding And Location Algorithm Based On Virtual Time Reversal

The detection of targets by electromagnetic waves is mainly divided into active detection and passive detection.With the rapid development of stealth and anti-radiation weapon technology,active detection mode needs external radiation electromagnetic energy,which makes it become the target of anti-radiation weapon seeking and attacking,so it is difficult to meet the application requirements in some battlefield environments.The passive detection does not require external radiation electromagnetic energy and has good confidentiality,the technology has been widely studied.Passive detection technology is usually based on radiation sources such as equipment that can transmit electromagnetic signals as the target,can complete passive direction finding and passive location two tasks.Passive direction finding is also the DOA estimation of the target,which only detects the direction information of the target.Passive location is to detect the specific location information of the target.At present,there are many methods for radiation source signal detection,but they have their own shortcomings.Some of them are limited by the antenna array,some have poor anti-noise performance,and some have complex calculation that are not conducive to practical applications.Therefore,how to make a passive detection technology which have good performance in complex electromagnetic environment without the limitation of array type and easy to realize in engineering has become the focus of current research.Time reversal mirror is derived from the multi-path effect and the idea of spatial matching filtering of matched filter of underwater acoustic channel.Then scholars apply the principle of time reversal focusing to the electromagnetic field.With the continuous development of technology,the concept of Virtual Time Reversal is further proposed.It is no longer to retransmit the received signal to the target domain,but to replace this process by mathematical calculation.The mathematical relationship between the signal and the virtual point in the virtual target domain is established,and then the computer calculation is used to find the target azimuth estimation.Because the equipment itself no longer needs to transmit the signal,it will not expose its own target.It is a passive direction finding method.Through repeated experiments,it is proved that the algorithm can detect in uniform linear array,circular array and cross array antenna array,and has the advantages of not limited by the type of antenna array.ion of the radiation source,so the calculation amount can be greatly reduced.At the same time,it has the characteristics of adaptive focusing and good anti-noise performance.Although this method is not limited by the array,the virtual search domain is different for different antenna arrays.Therefore,it is necessary to derive the mathematical model for the actual array to establish an effective virtual search area.It based on the virtual time reversal method,the virtual time reversal focusing method under the uniform linear array(ULA)is derived.Then,on the basis of this method,the passive detection algorithm for the radiation source target in the high altitude and far field is established,and the simulation experiment for the accurate estimation of the target direction and position is completed.The results show that this method has good anti-noise performance and directionfinding positioning accuracy,and is more conducive to the realization of passive detection equipment.The specific research contents of this paper are as follows:First of all,through the study of electromagnetic virtual time reversal focusing theory,starting from the uniform linear array,the virtual search domain of the basic array under the virtual time reversal method is established.The azimuth estimation method under the search domain is deduced,which lays the foundation for the derivation of the subsequent method.In order to realize the two-dimensional DOA estimation of high altitude and far field radiation source target,based on the method under uniform linear array,the uniform cross antenna array of two-dimensional DOA estimation is established which adopts a cross-line circular polarization.The array is reduced to two one-dimensional uniform linear arrays,and their virtual search domains are given respectively.The DOA estimation method under search domain is derived.This method is a kind of passive DOA estimation method which can maintain good direction finding accuracy in complex electromagnetic environment,and it is suitable for the design of hardware system because of its small amount of calculation.Therefore,it also gives a parallel design scheme based on FPGA.In order to apply to this design,the DOA estimation method of cross antenna array without central element is given.The simulation results show that the algorithm is the same as the traditional algorithm,and can achieve the passive DOA estimation of the target.The estimation performance advantage is more obvious at low SNR.The hardware design scheme is simulated and analyzed by the Vivado software of Xilinx Company,which proves the effectiveness and real-time performance of the design.Secondly,aiming at the problem that the virtual time reversal focusing theory ignores the energy loss in the process of signal propagation in the electromagnetic signal detection,so that the direct use of this method can only detect the target orientation but cannot obtain its specific position information.This paper combines the virtual time reversal passive DOA estimation method with the traditional passive direction finding cross location method,and uses the DOA estimation results of the target obtained by the multi-antenna array to obtain the specific position estimation of the target through mathematical calculation.The dual-station passive localization principle using uniform linear array in the plane is derived,and the localization performance is analyzed.At the same time,a virtual time-reverse passive location method based on uniform cross-antenna array is derived.The observation equations are established by using DOA estimation results,and solved by Tikhonov regularization total least squares estimation method.Finally,the estimated target position is obtained.The above algorithms are verified by computer simulation experiments to be feasible and effective.Finally,since the target direction finding methods mentioned above are all aimed at narrowband signals,and the signals of modern electromagnetic direction finding are all aimed at wideband signals with more information,the proposed method cannot be directly used for wideband signal direction finding after experimental analysis.In order to use the virtual time reversal focusing method to detect wideband signals,the widely used linear frequency modulation(LFM)signal is used as the target wideband signal.The LFM signal model under the time reversal array is established by using the uniform cross antenna array as the antenna array of the time reversal algorithm.The traditional ISM algorithm is optimized and the LFM signal received by the array is segmented.Combined with the propagation delay correction factor,a variable delay compensation virtual time reversal target direction finding method is given.The scheme also optimizes the calculation amount generated by the virtual search of multiple narrowband signals.The feasibility of the algorithm is verified by simulation.