| With the deepening of modernization,the development of urban underground space is more and more intense.In the early stage of development,there is no clear data backup for many underground pipelines,which brings great safety risks to the construction.During the construction,road collapse,pipeline fracture and other dangers often occur.Therefore,it is a significant research topic to detect underground pipelines quickly and accurately in advance and to grasp the information of underground substances in advance.Ground-penetrating radar(GPR)has the advantages of high resolution and detection of nonmetallic substances,and has been successfully applied in geological exploration,shallow pipeline detection and other fields.However,the interpretation of echo map is still dominated by experience and subjective judgment,and there are large errors.Antenna is the key part of ground penetrating radar,which greatly affects the quality of the system.Traditional commercial antenna bandwidth is narrow,impedance matching is not good,need to replace the antenna to adapt to different occasions and other problems.This paper takes shallow underground pipeline detection as the background,carries out pipeline forward simulation analysis,and designs a ground-penetrating radar antenna guided by ultra-wiband and high-gain antenna.The main research work of this paper is as follows:Antenna is an important part of Earth penetrating radar and its performance will have a significant direct impact on the system.Due to the narrow working bandwidth of traditional commercial butterfly antenna and poor impedance matching,the shortcomings such as the need to replace the antenna when applied in different occasions are more serious.In this paper,a ground-penetrating radar antenna with good comprehensive performance is designed based on the practical background of the exploration needs of shallow underground pipelines and guided by the ultra-broadband,high-gain and miniaturized antenna.Finally,the feasibility of the antenna performance is verified through the actual production and actual measurement experiments.The main research process and route of this paper are as follows:1.The detection method of ground penetrating radar,the working principle of ground penetrating radar system,the forward numerical simulation principle of ground penetrating radar and the main performance indexes of ground penetrating radar system are studied and analyzed.The influence of antenna parameters on ground penetrating radar system is analyzed.Based on the design theory of ultra wideband and high gain antenna,several main parameters affecting antenna performance are summarized,which provides a basis for antenna simulation design.2.The Finite Difference Time Domain(FDTD)numerical simulation method is studied,the difference equation of FDTD in three-dimensional and two-dimensional space is derived,and the absorption effect of Mur and CPML under different boundary conditions is analyzed and compared.Forward simulation experiments were carried out to study the electromagnetic wave propagation rule under pipelines of different sizes,depths,shapes and materials,and to provide reference for the interpretation of actual data by analyzing the spectrogram characteristics of different target bodies.3.The numerical simulation method of Alternating Finite Difference Time Domain(ADI-FDTD)is studied,and the two-dimensional space difference equation of ADI-FDTD is derived.The stability,dispersion characteristics and errors of the method are analyzed,and the characteristics that it is not constrained by stability are verified.Combined with the CPML boundary,the forward modeling example is analyzed to verify that it can be simulated with a larger time step,which can improve the forward modeling efficiency of ground penetrating radar.4.Study the design theory of butterfly antenna,carry out structural loading,enlarge the Angle,increase the shielding cavity,simulation design of a410mm*362mm*103mm ground-penetrating radar antenna,using the established test system,verify that the antenna working bandwidth is 491.25MHz-1762 MHz,the relative bandwidth is 112.79%.Impedance matching is good,and can be satisfied with shallow underground pipeline detection applications. |
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