Research On The Imaging Method Of Close Range Targets Broadband Digital Receiver Direction Finding Method

Passive detection broadband digital receivers are widely used in the military field due to their advantages of high concealment and low system cost.As an important component of the receiver,radiation source direction finding technology has always been a focus of attention.Considering that electromagnetic signals in practical environments have characteristics such as wide frequency band range and high signal density,and that channelized receivers have the advantages of broadband monitoring,receiving multiple signals,and narrowband processing,this paper studies different direction finding methods and their FPGA simulation verification under the polyphase filtering DFT channelized structure.The specific content is as follows:(1)Analyzed the basic principles of broadband digital receivers and designed a polyphase filtering DFT channelization structure.Firstly,the channelized structure of polyphase filter is derived according to the actual needs to process the signals channelized,which mainly involves the specific process of prototype filter design,signal extraction,polyphase filter and channel division.Then,the method of signal detection and channel decision is given.Finally,the correctness of the channelized structure design is verified by simulating multiple signals in the frequency range of 1.2GHz～2.3GHz.(2)To address the issue of the impact of different baseline combinations on direction finding accuracy under two-dimensional circular array interferometers,phase interferometer direction finding for parallel and vertical baseline groups was studied,as well as related interferometer direction finding for guiding baseline improvement sample libraries.The parallel baseline group selects different parallel baselines for deblurring by dividing the circular array area.The vertical baseline group deblurring is achieved through two sets of the longest vertical baseline groups.Simulation results show that they can effectively solve phase ambiguity,but the direction finding accuracy obtained by the vertical baseline group is higher than that of the parallel baseline group.In addition,the correlated interference direction finding method guided by the baseline guides adjacent array elements to form a direction finding baseline group based on the actual incoming wave direction,establishes a discrete sample library,and optimizes the sample library interpolation.Simulation verifies that this method can achieve direction finding accuracy of less than 1 °.(3)A direction finding method based on improved time difference estimation is proposed to address the issue of the impact of time difference estimation accuracy on time difference direction finding methods in channelized receivers.This method first intercepts pulses to maintain their similarity,and then combines cross correlation and parabolic fitting to estimate the time difference.This not only reduces the amount of subsequent data operations,but also improves the accuracy of time difference estimation,eliminating the problem of time difference estimation accuracy limited by sampling intervals caused by channelized structures.Through simulation experiments analyzing the direction finding results of signals at different signal-to-noise ratios,pulse widths,baseline lengths,and angles,it can be seen that this method can achieve an angle measurement accuracy of 1 °when the baseline length is 100 meters and the direction finding angle range does not exceed 45 °,and can adapt to a signal pulse width range of 0.1us-10 us.(4)Corresponding FPGA simulation verification schemes have been designed for the relevant interferometer direction finding and time difference direction finding mentioned above.The direction finding of the correlation interferometer is composed of the subtractor module,the module and the bubble sort module.The sample library is ingeniously established,which avoids the angle operation after matching the phase difference and effectively reduces the amount of calculation.The time difference direction finding module is designed using the design concept of a state machine,which consists of an address logic control module,a multiplier,and an accumulator module.The correctness of the correlation interferometer direction finding module and the time domain cross correlation module was verified through simulation.