Research On Detection Method Of Faint Target Of Passive Radar Based On Differential

Passive radar uses space-existing electromagnetic waves as irradiation source for moving target detection,and adopts dual/multi-base operation mode,which has the advantages of high survivability,no electromagnetic pollution,low cost,etc.It can also perform lowaltitude and stealth target detection,and has important application prospects in coastal warning,target monitoring,assembly security,etc.However,compared with traditional active radar,the radiation power of passive radar irradiation source is generally low and mostly continuous wave signal with strong multi-path clutter,which leads to weak echo signal and requires long time signal accumulation technique to enhance the signal energy.In this paper,we conduct an in-depth study on key issues such as external radiation source radar echo clutter suppression and coherent accumulation methods,which mainly include the following four aspects:1.The calculation method of coherent accumulation gain of passive radar when distance walk and Doppler diffusion exist is studied.Since the coherent accumulation gain is linearly related to the coherent accumulation time and its value is the product of the coherent accumulation time and the effective bandwidth,there is no specific calculation method for the accumulation time and accumulation gain when there is distance walking and Doppler diffusion.In this paper,the boundary conditions of coherent accumulation time for distance walking and Doppler diffusion under uniform motion model and uniform acceleration motion model are analyzed,and the quantitative relationship between coherent accumulation gain and coherent accumulation time when distance walking and Doppler diffusion exist separately and simultaneously is given.2.A frequency domain processing-based clutter cancellation algorithm for passive radar is proposed.The passive radar not only receives the reflected signal from the target,but also receives the direct wave and multi-path reflected signal from different feature environments at the same time by the echo antenna.The direct wave and multi-path signals are generally tens of decibels higher than the target echo,resulting in the peak of the target will be submerged in the direct wave and multi-path signal related sub-flap can not be detected.The existing methods for eliminating clutter from external radiation sources,such as LMS and RLS algorithms need to iterate to find the best,its convergence speed and elimination accuracy can not be balanced.The ECA algorithm requires the inverse of the delay matrix,which is too complex when the order of cancellation is large and the signal accumulation time is long.Therefore,this paper proposes a passive radar clutter cancellation method based on frequency domain processing,which is based on frequency domain processing to directly estimate the position and amplitude of multi-path clutter.In the case of strong clutter,the algorithm can use the estimated parameters to directly eliminate multi-path clutter.When the multi-path clutter is weak,the multi-path amplitude estimation error caused by the target amplitude is large.The algorithm can be combined with the ECA algorithm to greatly reduce the subspace order of the reference signal and its delayed signal tensor in the ECA algorithm and reduce the ECA algorithm operation.3.A differential correlation algorithm based on the two-dimensional Fourier transform is proposed.In order to improve the distance resolution of radar target detection,the passive radar selects a larger bandwidth of irradiated source signal for target detection,and the speed of aircraft,ships,missiles and other targets are getting faster and more maneuverable,which leads to cross-distance unit and Doppler unit walk when the target is coherently processed in a shorter period of time.And with the development of stealth technology,the target RCS is getting smaller and smaller,and the long time accumulation to the target cannot be avoided.The joint processing of multiple signals can effectively improve the target output signal-to-noise ratio,but the single-site passive radar only receives one way echo signal,so this paper analyzes the processing benefits that can be achieved by converting a single signal into a multiple signal using differential processing and performing joint processing on this multiple signal.The analysis shows that the target output signal-to-noise ratio can be effectively improved if the processing method used can change the target differential signal in the processed signal of each channel to the same signal while the cross term and noise differential signal are not correlated.However,the correspondence between the signal and the noise at different differential orders does not change after using R-D processing for multiple signals separately,and the superposition of the results after multiple signals are processed separately will not only improve the accumulation gain of the target,but also improve the accumulation gain of the noise.Therefore,this paper proposes a differential correlation method based on the twodimensional Fourier transform.This method can obtain higher target output signal-to-noise ratio than distance Doppler processing when the echo signal-to-noise ratio is higher than2/N.Firstly,the reference signal and the echo signal are processed by differential dot product of different orders,and the multiple differential auto-correlation signals of different differential orders are obtained respectively.And then,using Fourier transform,the reference differential signal and the return differential signal of corresponding orders are processed in the frequency domain,and after processing,the target part of each return differential signal is changed into an exponential signal containing only the target and Doppler,which eliminates the modulated phase of the target signal itself,and then the twodimensional Fourier transform is used to jointly accumulate the multiple signals,which can change the target return signals under different differential orders after the accumulation,the target signal gets two coherent accumulation gains,while the cross term and noise differential signals only get two non-coherent accumulation gains,thus improving the output signal-to-noise ratio of the target.Finally,the algorithm is verified using simulation tests and real tests.4.A differential cancellation based passive radar target detection algorithm is proposed.The echo signal-to-noise ratio is greater than 2/N,which is a necessary condition for the proposed differential interpolation algorithm based on 2D Fourier transform to obtain higher signal-to-noise ratio than the output of range-Doppler processing target,which also means that there are some limitations in the performance of the differential interpolation algorithm based on 2D Fourier transform at very low signal-to-noise ratio.Therefore,this paper proposes the method of differential combined with quadratic pair cancellation to preprocess the echo signal,change the single-way signal into multi-way signal,and the target part under different differential orders is completely correlated after processing,while the cross term and noise differential signal are transformed into uncorrelated signal,and then the range-Doppler processing is used to jointly process the above signals to improve the target echo output signal-to-noise ratio.The target detection algorithm based on differential pair-cancellation of external radiation source radar has higher target detection performance than the range-Doppler algorithm and the differential correlation algorithm based on the two-dimensional Fourier transform at very low signalto-noise ratio,but its detection range is limited by the order of the second pair-cancellation pair-cancellation,which can only detect targets within a specific range.Finally,the effectiveness of the algorithm is verified using simulation tests and real tests.