Research On Decontamination Methods Of Ionosphere And Detection Methods In Short-wave Passive Radar

The external radiation source radar itself does not emit electromagnetic waves,but "passively" receives electromagnetic waves radiated by third-party radiation sources.The receiver receives electromagnetic waves refracted from the ionosphere.Based on the fractal theory,a model was established to demonstrate the relationship between the porous graphite permeability and the fractal dimension.It can predict the permeability of porous graphite and show the effects of the pore size on the permeability.Due to the time-varying and non-uniform structure of the ionosphere,the electromagnetic waves propagating in the ionosphere are modulated by phase pollution.Thus the echo spectrum is broadened or split and the target is submerged by the clutter power spectrum,which affects the detection performance of the radar receiver.In this thesis,the author first derives the signal processing model at the receiving end of the radar based on the working mechanism of the external radiator radar.The echo signal after matching and filtering is corrected for phase disturbance,and the corrected echo is used for target detection.Secondly,analyze the formation mechanism of the first-order sea clutter,establish a sea clutter echo model,and analyze the influence of parameter changes on the sea clutter echo spectrum.Then use the sea clutter model as a reference to correct the ionospheric pollution phase.Thirdly,starting with the generation mechanism of phase pollution in the ionosphere,the influence of fast and slow phase path disturbances on the echo spectrum is analyzed.The relationship between the degree of phase pollution and the amplitude of the pollution function and the modulation frequency are characterized as well.The mechanism of phase pollution correction of PGA,MESE and PPS is theoretically analyzed.For the PPS algorithm,the influence of different segmentation methods on the correction accuracy is studied,and the optimal segmentation method is selected.In this paper,the algorithm of phase pollution correction in the ionosphere is studied.The simulation compares the maximum pollution frequency that the three algorithms can recover.Under the same pollution function and different modulation frequencies,compare the ability of the three algorithms to decontaminate fast and slow phase path disturbances.Considering the application scope of the algorithm,the complexity of the algorithm,the estimation accuracy and other factors,different decontamination algorithms are selected in different ionospheric environments.Finally,for the echo data after matched filtering,a constant false alarm detector is used for target detection.The simulation analyzes the detection performance of CA-CFAR,OS-CFAR,GO-CFAR and SO-CFAR detectors in different clutter backgrounds.The above-mentioned three kinds of detectors all need specific clutter background.In order to enhance the performance of the detector under different backgrounds,the application scenarios of the adaptive detector VI-CFAR are simulated and analyzed.For the CA-CFAR detector,the deleted unit is combined with it to get an improved CCA-CFAR detector.Pass the decontaminated data through the constant false alarm detector and select the optimal detector.