A Study Of Interference Fringe Phenomenon And Restraining Technique In Single-Frequency Mechanism Penetrating Radar Imaging

Single-frequency mechanism penetrating radar is mainly applied to thin layermedia penetrating detection imaging. The radar has intuitionistic imaging, high azimuthresolution, and high equipment cost-effective, radiating safety and so on. It’s a greatpotential for development of the nondestructive imaging detection technology. In theuse of radar planar imaging scanning, there will appear the regular changes of light anddark stripes phenomenon in the image when medium is inclined. These stripes canseverely reduce the target imaging effect and restrict the actual detection for targetidentification. My tutor and I introduced the discovery of this fringe phenomenon forthe first time at the GPR2012meeting in public. Because the literatures at home andabroad do not study specially this fringe phenomenon, this paper study about theforming mechanism, stripes characteristics and restraining technology of the fringephenomenon.Based on the widely-known of the Single-frequency mechanism penetrating radartechnique and penetrating detection application, we study thorough the interferencephenomenon. Through theoretical analysis and experimental demonstration, theinterference fringe phenomenon is composed superimposition waves of an antennacoupled wave, the reflected wave of target and medium surface, with the antennaposition changing regularly. This kind of phenomenon and optical interferencephenomena are similar, so it is called interference fringe phenomenon.Based on the theory of electromagnetic field, the interference fringe phenomenonmechanism is studied. In the second chapter, the electromagnetic theory in the near fieldscanning is deduced. The Maxwell equations and boundary conditions in theelectromagnetic field theory are used to deduce the field distribution of the horn antennaaperture and the distribution of electromagnetic field in the horn antenna. The auxiliarysource method calculates the near radiation field of the antenna. The theory is derived tocalculate the intensity of echo received by antenna at the different positions.Reference optics interference principle, in the third chapter the near field radiationsource model is constructed. Respectively, the antenna coupling wave, the direct waveof medium surface and reflection wave of target in the medium are analyzed. Analysisshows the radar scanning along the inclined medium surface line or plane, distance ofthe antenna to the medium is the function of medium inclined angle. Gradual changingcauses the phase of the reflected wave changing. So the medium surface reflected waveis the main reason for the interference fringe phenomenon. On this basis, therelationship between the interference fringe and the inclined angle of medium isdeduced, and the effect of medium thickness on the interference fringe phenomenon isdiscussed further. The relationship between the medium thickness and the interference fringe is analyzed.In order to verify the result of theoretical analysis, based on the formula of nearfield electromagnetic theory in the second chapter, precise electromagnetic model isestablished and the electromagnetic simulation is calculated. Comparing theelectromagnetic simulation results with the calculation results of point source radiationmodel, the theoretical analysis of the interference fringe phenomenon is verified. Inaddition, the measured scanning data also verifies the theoretical analysis results in thepaper.For restraining or removal of interference fringe to improve the radar imagingeffect, the FK filtering algorithm and the signal parameter model filtering algorithm forthe interference fringe are put forward in the fourth chapter. FK filter is based on thecharacteristic of the interference fringe concentrated in the center region in thefrequency-wavenumber domain. In frequency-wavenumber domain, center region isremoved and two-dimensional inverse Fourier-transform changes the data into spatialdomain to achieve the purpose of eliminating interference fringe. The interferencefringe signal parameter model filtering algorithm is based on the interference fringeformula in the third chapter. The reference wave is constructed. According to the filteredimage, the target function is established, and the parameters are optimally searched inorder to optimize the filter processing results. In this chapter, the measured data isfiltered, and the results show the interference fringe FK filtering algorithm is widelyused and has good effect. The interference fringe signal parameter model filteringalgorithm has strong constraint conditions and the effect is best, but the computationalcost is large in the filtering process.