| Biological radar is an instrument which is used to detect the geographic informationand life information of life body in an unknown area. Its applications include disaster relief,medical application, security application and fight against terrorism and other occasions.The geographic information of life body is the spatial location of life body in an unknownarea. The life information of life body is respiratory rate, heartbeat rate and otherparameters.Biological radar obtain horizontal tomography image of the unknown region throughcomputer tomography, and the geographic information of life body can be determined inimage. Biological radar often needs to penetrate obstruction. The obstacle is manifested asa strong direct wave in the echo signal of radar, which affect to distinguish the target in theimage. Micro-Doppler effect is often used when using radar to detect human breathing,heartbeat and other micro-information. The difficulty is that weak signal is needed to bedetected in strong noise. Existing research results can not completely solve the problem ofdirect wave removal and the detection of breathing rate and heartbeat rate, so theapplication of it has certain limitation. Therefore, in-depth study in the echo signalprocessing and system parameters of biological is great significance to improve itsperformance. Doing research for the above problem in this paper, the main content is asfollows:(1)The research for near-field imaging algorithm of ultra-wideband steppedfrequency continuous radar. Firstly, the concept of near-field imaging is introduced. Themathematical model of the forward problem is established for ultra-wideband steppedfrequency continuous wave biological radar. Then synthetic aperture technology in biological radar imaging is introduced, The application of frequency-wavenumber domainimaging algorithm used in ultra-wideband stepped frequency continuous radar is studied,and the imaging performance of the algorithm is analyzed by simulation.(2)The research for direct wave suppression method of biological radar. Firstly, theeffect of direct wave to the imaging of biological radar is analyzed by theory. Fordeficiencies or limitations of traditional method used in the removal of direct signal, thesingular value decomposition method and complex FastICA method for removing directwave is proposed in this paper. The characteristic that the direct wave component accountsfor the main component in echo data is used in the singular value decomposition method.This method overcomes the shortcoming of the traditional Interference Canceling methodthat the amplitude of target signal is weakened after removing the direct signal. The signalto noise ratio of image is improved, and algorithm is fast. The complex FastICA method isproceed from the data structure of the echo signal.It is based on the higher order statisticscharacteristic of signal, and can decompose the signal into multiple independent signalcomponents, makes the strongest non-Gaussian among the various components of thesignal. Finally, the feasibility and effectiveness of the singular value decompositionmethod and the complex FastICA method is veritied in the experiment. The definition ofsignal to interference ratio of energy is proposed in this paper, and the comparement isdone among of Interference Canceling method, singular value decomposition method andcomplex FastICA method using two evaluations of signal to interference ratio of energyand signal to interference ratio.(3)The research for micro-Doppler information detection method of life body. Forthe deficiencies of detecting life body micro-Doppler information methods usingtraditional single-frequency continuous-wave emission signal, which is that the noisesuppression capability is weak, micro-Doppler information of multiple targets can not bedetected and the location of target can not be obtained when detecting micro-Dopplerinformation, ultra-wideband stepped frequency continuous wave emission signals anddistance domain filtering method is proposed in this paper for detecting life body micro-Doppler information. Firstly, the mathematical modeling of life body breathingsignal detection for ultra-wideband stepped frequency continuous wave biological radar isdone. Simulation is done for one-dimensional imaging of target in distance domain ofdifferent respiratory rate. Through the analysis of simulation results, the respiratory signalis almost attached to one-dimensional imaging of distance domain when the respiratoryrate is less than 1Hz. The simulation of interception in the one-dimensional imaging ofdistance domain is done, and the conclusion is obtained that the respiratory signal is notlost when doing interception at a certain distance of both sides for one-dimensionalimaging of distance domain. Based on the above conclusions, a distance domain filteringmethod is proposed in this paper for eliminating the noise and interference, and achievingthe detection purpose of breathing frequency of life body. The method described above isverified by experiment. In single body experiment, the respiratory rate can be detected. Indouble body experiment, the detection error increases due to the presence of multipathinterference, and even the respiratory rate detection fails. For strong background noise,which affects the judgement for one-dimensional distance domain imaging of target, adistance domain peak tracking method is used in this paper. This method can locate the lifebody and detect its respiratory rate in the case of strong background noise.(4)The research for measurement system parameters and sampling time cumulativelength of respiratory rate detection. In the measurement system, the parametersinconsistency of each frequency point of the antenna, the stepping frequency interval of thetransmitted signal and the IF filter bandwidth settings of the receiver affect measurementgreatly. In this paper, through the analysis of measurement environment and theoreticalderivation, the phasor difference method is proposed for removing the inconsistency ofantenna, and reasonable set of step frequency interval and the IF filter bandwidth.Then thispaper analyzes the effect of sampling time cumulative length for the detection ofrespiratory rate.Combined with the previous experimental results, a reasonable samplingtime cumulative length is proposed. Finally, the error and resolution of the respiratory rate detection based on the distance domain filtering method are analyzed after themeasurement system parameters and the sampling time cumulative length is determined.
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