Research On Direction Of Arrival Estimation For Integrated Active-Passive Digital Array Radar

The application of integrated active-passive digital array radar(DAR)becomes wider in complicated environment for its excellent performance in detection,recognition and flexible work mode.In practical applications,the presence of array error,low signal-to-noise ratio(SNR),much limited snapshots,correlated or coherent situation due to multipath propagation will affect the performance of existing direction of arrival(DOA)estimation methods.When the digital array radar works with active mode,the wave form and parameters of the reflecting signals are usually known.The apriori information can be used to improve the performance of DOA estimation method.This dissertation focuses on the problem of DOA estimation under unknown mutual coupling,with coherent signals,with wideband signal and known Chirp signal.The main contributions in this dissertation are illustrated as follows:Firstly,for the DOA estimation in the presence of unknown mutual coupling,we propose a real-valued DOA estimation method and a coherent signals DOA estimation method in the presence of unknown mutual coupling.By taking advantage of the special structure of the mutual coupling matrix for ULAs,the effects of mutual coupling can be eliminated by a group of auxiliary sensors.To decrease the computational complexity,the proposed method finds signal DOAs by spectral search over only half of the total angular field-of-view with a real-valued noise subspace.When considerating coherent signals,a Toeplitz matrix,whose rank is independent of the coherency between impinging signals,is reconstructed to eliminate the rank loss of the spatial covariance matrix.Then the DOAs of coherent signals under unknown mutual coupling can be estimated accurately.Secondly,for DOA estimation of wideband signals,we propose a novel channelization-based DOA estimation method for wideband signals.The proposed method splits the wideband array output into multiple frequency sub-channels and estimates the signal parameters using a digital channelization receiver.Based on the output sub-channels,a channelization-based incoherent signal subspace method(Channelization-ISM)and a channelization-based test of orthogonality of projected subspaces method(Channelization-TOPS)are used to estimate the DOA of wideband signals.The proposed channelization-based method isolates signals in different bandwidths reasonably and improves the output SNR.Besides,the parallel processing architecture makes it easy to implement on hardware.Considering the scenario that uncorrelated and coherent wideband signals coexist,we exploit the property of oblique projection to eliminate the contributions of uncorrelated signals from the array covariance matrix.Then the DOAs of uncorrelated signals and coherent signals can be estimated respectively at two different stages.It makes the method resolve more sources than the array elements.Thirdly,we propose a novel extended-aperture direction of arrival(DOA)estimation algorithm based on fourth-order cumulants(FOC)using sparse Bayesian learning.A FOC sparse model which indicates signal directions is derived.Then the sparse Bayesian learning(SBL)technique is employed to estimate the DOAs.The reconstructed FOC vector extends the array aperture and improves the signal-to-noise ratio(SNR).So the proposed method can resolve more sources with lower computational complexity.To avoid the errors caused by mismatches between the true DOAs and the sampling grid,the deviations between the true DOAs and their nearest grid points are jointly estimated during the procedure.Finally,we focus on the DOA estimation of Chirp signals with known parameters when the radar works with active mode.We proposed a novel DOA estimation method which including beamforming,pulse compression and coherent integration for narrowband Chirp signals.The proposed method can improve the SNR substantially,so the performance on DOA estimation accuracy and angular resolution will be better.As for DOA estimation of broadband chirp signal,the wideband chirp signal becomes a short pulse which is approximated by a sinc function with the use of matched filter.Based on the covariance matrix of the sinc function,the proposed method constructs a new signal model in which the steering vector is independent of the frequency and depends only on the DOAs of incident signals.Then existing narrowband DOA estimation methods can be applied to estimate broadband chirp signals DOA.Simulation results demonstrate that the proposed algorithm shows superior performance in DOA estimation of the broadband chirp sources.