Study On Radio Frequency Interference And Clutter For Bistatic High-frequency Surface Wave Radar

Much attention has been paid to HF surface wave radar for its ability to detect theover the horizon targets. The low altitude and near ranges are blind spots ofconventional microwave and Sky Wave Over the Horizon Radar respectively, HFSWRcan compensate these spots completely. The long distance and early radar surveillance,anti stealth, anti altitude penetration, and anti radiation missiles were the decidedadvantages of HFSWR. However, long wavelength of transmit leads to the problems oflarge position, difficulty of location chosen, low of the angle resolution, and badflexibility. The detection capability of HF surface wave radar is also influenced byinterferences and clutters especially the radio interference and the ionospheric clutter.Based on the discussion of coast ship bistatic surface wave over the horizon radar,this dissertation focuses on the design of distributed subarrays, the DOA estimation fordistributed subarrays, calibration of arrays which are on the coast, the methods of radiointerference suppression, the ionospheric clutter modeling and the study of suppressionmethod for ionospheric clutter in bistatic HFSWR with distributed subarrays.Themain content of our studies are summarized as follows:1. Distributed bistatic surface wave radar is designed and the DOA estimation inthis new radar is studied. Firstly, the concept of distributed bistatic surface wave radar isproposed for the problem of large position, difficulty of location chosen, low of theangle resolution, and bad flexibility. The new radar reserves the Synthetic Impulse andAperture Radar mechanism (SIAR) and the moving receive plat over ocean, the transmitarray using the distributed subarrays mechanism which makes the new radar havemonostatic MIMO system and bistatic MISO system. Secondly, the waveform oftransmit is proposed. Based on the analysis of signal processing, we can obtain theequivalent receive array models in two systems. Lastly, this dissertation focuses on theDOA estimation methods in the new radar. After the analysis of the DOA estimationproblem in two systems, the new DOA estimation method based on compressed sensingis proposed. The new method can estimate the target’s information with a few of sampledata, reduce the processing complication, and avoid the angle ambiguity. Simulationshows the advantages of distributed subarrays bistatic surface wave radar, the problemsusing the conventional DOA estimation methods and the validity of the new DOAestimation method based on compressed sensing.2. Transmit receive array of distributed bistatic surface wave radar is calibrated. Based on the analysis of array error in two systems, a strategy of transmit array andreceive array error calibration in these systems is proposed. Firstly, transmit array erroris calibrated in monostatic MIMO system, the error calibration technique is same ascoast ship bistatic surface wave over the horizon radar, by using the direct wave, themoving receive plat can calibrate the transmit array error with Covariance MatrixFitting(CMF) method and Subspace Fitting(SF) method respectively; Receive arrayerror is calibrated in bistatic MISO system, by using the echo from large ship, the strongradio interference and the ionospheric clutter, the receive array on the coast can achievearray error calibration with auto calibration method based on Multiple SingalClassification (MUSIC) method. Because of the large number of equivalent receiveantennas, this dissertation adopts the strategy that only a part of the equivalent receiveantennas are calibrated. This dissertation also presents the Cramer Rao Bound(CRB) ofarray error calibration. Simulation shows validity of the transmit array and receive arrayerror calibration strategy.3. Radio interference suppression of high frequency radar is studied. Thisdissertation focuses on distributed subarrays bistatic surface wave radar. After theanalysis of radio interference’s characteristics in time domain, range domain, dopplerdomain and space domain, we introduce the excising method in time domain, indicatethe several disadvantages of this method. Then, the radio interference suppressionmethod based on compressed sensing is proposed. Also, by using the interference’scharacteristics in time domain, this new method can obtain target’s range informationand doppler information accurately with a few of "cleanly" data. This dissertation alsoproposes a new radio interference suppression concept by using Blind Signal Processing(BSP).Because of the independence between single frequency radio interference andtarget echo in a periodicity, we can separate the single frequency radio interference fromthe target echo. Simulation shows validity of the radio interference suppression methodbased on compressed sensing and the radio interference separation method.4. Ionospheric clutter in bistatic system and suppression method is studied. Firstly,we analyze the cause for the form of ionospheric clutter in high frequency radar, thespace domain and doppler domain characteristics in bistatic system, and show therelation with azimuth, elevation and cone. We also analyze the components of dopplerincluded in the echo which are received by moving receive flat, and sum up theionospheric clutter transmission characteristics. Secondly, we achieve the ionosphericmirror refraction clutter model and ionospheric diffuse reflection clutter modelrespectively by using random signal modeling method. Lastly, we propose "time domain signal" clutter suppression method based on the eigenvalue decompose. This methodcan suppress ionospheric mirror refraction clutter availably. This dissertation shows thesimulation result of ionospheric clutter and validity of "time domain signal" cluttersuppression method.