A Study Of Unambiguous Direction Finding Algorithm Based On Long Baseline For Satellite Passive Detection

Applying the electronic reconnaissance equipment on the satellite platform to intercept,process and estimate the parameters of the radiation source to determine the target location has the advantages of far detection-range,strong viability and monitoring in all-weather conditions.The direction of arrival(DOA),which is determined by the relative position between the observing platform and the radiation source,is one of the important parameters that characterize the emitter's features in the complex electromagnetic environment.However,the direction finding(DF)performance of the satellite passive detection is usually limited by the size and load capacity of the satellite platform.Thus,how to improve the DF accuracy of the emitter under the condition of limited size and load capacity of the satellite is one of the key technologies of the satellite passive detection.It can reduce the complexity of the DF system and meanwhile guarantee the DF estimation accuracy when the long baseline DF system,whose baseline is much longer than the emitter wavelength,is used to estimate the parameters of the emitter.However,the serious DF problem may make it difficult to locate for the satellite passive detection when the long baseline DF system is utilized to estimate the parameters of the emitter.To deal with the DF ambiguity problem in the long baseline DF system,in this dissertation,we study mainly on these issues,including the ambiguity solving method in the long baseline DF,the unambiguous parameters estimation of multi-emitters with overlapped time and frequency,and the design of the low-complexity electronic reconnaissance array and unambiguous DOA estimation in a very wide frequency band.The main works in this dissertation can be summarized as follows:1.The problem of unambiguous parameters estimation of the emitter in the presence of ambiguity in the measured phase-differences with a circular array interferometer is studied.First,by analyzing the variation of the phase-differences between the adjacent array elements of the circular array interferometer,we find that the unambiguous phase-differences between adjacent array elements present a sinusoidal variation as a function of the element series.Thus the two-dimensional angle parameters of the emitter can be estimated by detecting the parameters of the phase-difference curve.Then we propose two algorithms for the unambiguous parameters estimation of the emitter,which are based on the recovery of the phase-difference curve and the parameter detection of the phase-difference curve by the randomized Hough transform,respectively.Both algorithms take the ambiguity of measured phase-differences into consideration,which can greatly improve the DOA estimation performance.Besides,they can also flexibly select the baseline combination and utilize all the measured phase-differences to estimate the angular parameters of radiation source,which can effectively improve the accuracy and robustness in wide frequency band direction finding.2.To address the problem that it is impossible to estimate the unambiguous angles of multiple time-frequency overlapped emitters for the traditional rotating interferometer,we propose an approach for multiple emitters' parameters estimation with rotating interferometer by using the virtual circular array processing.First,the virtual circular array data is constructed by taking conjugate multiplication of the two channel data received by the rotating interferometer.And based on the phase mode excitation,the virtual linear array data is obtained by transforming the virtual circular array data from element space to beam space.Then,the unambiguous angle parameters of the multiple emitters are estimated in the beam space domain.Both theoretical analysis and simulation results demonstrate that the proposed algorithm can realize the unambiguous DOA estimation for the multiple time-frequency overlapped emitters without increasing the receiving channels.3.The problem of the low-complexity wideband electronic intelligence(ELINT)array design and the unambiguous multi-target parameters estimation is studied.First,we introduce the characteristics of co-prime array and analyze the feasibility of the application of the co-prime array in the ELINT array design and multi-emitters parameters estimation in a wide frequency band.And,we build an array optimization-design criterion for the wideband ELINT co-prime array from the perspective of reducing the mutual coupling effect and the unambiguous DOA estimation of the multi-emitters in the wide frequency band situation.Then,two methods of the wideband ELINT array design are proposed,which are based on the double parallel co-prime array structure and co-prime planar array structure,respectively.Both theoretical analysis and simulation results demonstrate that the proposed algorithms can not only reduce the mutual coupling effect between antennas greatly,but can also realize the unambiguous DOA estimation with high accuracy in a wide frequency band.