Multi-frequency MIMO HF Radar Key Technologies Research

HFSWR is an effective surveillance radar system, which can detect the horizonstealth targets over the sea, usually adopts wide beam irradiation, receives the echonarrow beam in single direction. Since in HF band the target characteristics in theRayleigh region or resonance regions, uncertain target attitude and RCS fluctuationscan easily lead to weak echoes and missed targets. To overcome the targetscintillation, the study takes full advantage of RCS differences in differentfrequencies and angles, combining multiple-input multiple-output (MIMO) systemand HF radar, exploiting the advantages of the MIMO system to enhance the radarsystem time, space, frequency management DOF, synthesizing multi-directional,multi-frequency target echo information effectively, to improve the resolution of theobjective system, and improving the system’s resolution. Therefore, the researchabout key technologies of MIMO system and HFSWR combination has importantsignificance.In this study, we combined the MIMO system with HFSWR characteristics, andestablished a multi-carrier MIMO HF radar model which is different from thegeneral MIMO radar. This research established a centralized and distributed MIMOradar model, for different model proposed an effective signal processing algorithms,and obtained some positive significance and reference value methods andconclusions. Overall, this study includes the following aspects:First, the research improved MIMO ambiguity function to adapt complexMIMO radar system speed range resolution analysis, breaking the traditional theoryof ambiguity function limitations. This paper presents a discontinuous spectrumMIMO HF radar ambiguity function, and discusses spatial and temporal couplingunder collocated MIMO model which adopts different carrier frequency diversitytransmission signals, effectively assesses the range resolution of the system, andobtains discontinuous spectrum waveform parameter selection criteria; furtherextends the traditional ambiguity functions to evaluate system spatial resolution, andgets distributed MIMO radar sensor deployment general law in a multi-carrierMIMO model. This study proposes improves MIMO radar ambiguity functionglobally for high resolution analysis, which has important significance for thesubsequent key issues raised and resolved.Second, in order to effectively improve HF radar range resolution, fordiscontinuous spectrum signal generating higher sidelobes shortcomings, this studyproposes two kind of discontinuous spectrum signals to solve higher sidelobe problem-the receiving sidelobe suppression and transmitter discontinuous spectrumwaveform design. Different from the previous time multiplexing structurediscontinuous spectrum waveform, this study adopts antenna diversity to transmitdifferent carrier frequency phase coded signal, the receiver suppress highersidelobes around the mainlobe after signal coherent processing. Based on convexoptimization algorithm we design sidelobe suppression filter to remove pseudo peakwhich is produced by a finite length data sliding window, effectively solving weaktargets are submerged by higher sidelobes under multi-target environment. Theproposed algorithm has good real-time and simple characters, is easy to practicalimplement. Based on the transmitter waveform design, the study obtained therelationship of waveform between average passband-stopband power ratio and theautocorrelation sidelobe level, and proposed waveform optimized cost function. Byquantum genetic algorithm we optimize the low autocorrelation sidelobes waveformto obtain the desired results, the optimized waveform under constraint spectrumachieved the optimal sidelobe levels. This chapter on discontinuous spectrum signaldesign improves HFSWR working performance under harsh electromagneticenvironment.Third, in the perspective of HF radar poor angle resolution, different from theprevious model of virtual MIMO array technology, the study proposed amulti-frequency focus algorithm to synthesize virtual array aperture. For virtualaperture array element interval greater than half the wavelength, the beamformingwill generate grating lobes, this study further proposed based preconditionedconjugate gradient method to reconstruct non-uniform spatial information efficientlyto suppress higher grating lobes. In the reconstruction of the standard frequencyuniform spatial information, high-dimensional equation need to solve, theintroduction of the pre-conditions significantly improves the convergence speed.Meanwhile, for different amplitude and phase response, Doppler and SNR of thedifferent frequencies, we proposed corresponding preprocessesing, and analysis howthe transmitter carrier frequency selection impacts on the overall performance of thespatial synthesize in addition. Multi-carrier MIMO spatial synthesis proposes a newsignal fusion ideas, effectively extends the HFSWR aperture size.Fourth, this study established a multi-carrier Distributed MIMO HF radarmodel, which exists space and Doppler domain sparse sampling problem, andproposed distributed radar system algorithms based on compressed sensing. In thisstudy, we adopt inhomogeneous period to radiates phase-coded multi-carrier signal,that can reduce multi-pulse system radar different nodes’ data transfer burdeneffectively. For sparse echo signal recovery problems, we construct a spatial andDoppler domain in single CS matrix, the algorithm figure out multistatic distributed system centralize processing and distributed systems target location ambiguityeffectively. For mesh refinement causing CS matrix column stronger correlation,multi-frequency information is introduced, it is better to solve CS matrix RIPconditions. Furthermore, in view of the actual situation, unknown differentdirections response results in reconstructing inaccurately, we propose additionalrandom phase CS matrix to improve target location errors. Finally, the studyanalysis the CS matrix column vectors correlation relationship between theestimation error and the number of pulses, and the spatial resolution of the griddivision criteria. This study is important theoretical basis of CS distributed MIMOradar model applied to practical application.