| With the rapid development of China's social modernization process,the ground penetrating radar(GPR)as a high-efficient,high-resolution,non-destructive geophysical detection instrument,has been widely used in the urban underground space development,pipeline and road cavity inspection,transportation Engineering quality inspection,underground resource exploration and other fields.Compared with traditional detection technology,GPR technology has higher accuracy in shallow detection.And the step-frequency continuous wave ground penetrating radar based on the network analyzer has a higher resolution in many systems of GPR because it is measured by sweeping frequency,and the theoretical frequency sweep bandwidth can reach any width.Antenna as the key technology of the entire GPR system,plays a crucial role in the high-resolution detection.The antenna of GPR system should have the characteristics of ultra-wideband frequency,high detection resolution,good radiation direction and miniaturization,so as to improve the overall performance of GPR.In this paper,on the basis of the traditional bow-tie antenna,from adding arm and truncating arm two structures respectively which designed a drop-shaped ultra-wideband antenna working in the low frequency and a tripod ultra-wideband antenna working in high frequency.On the one hand,it expands the antenna bandwidth and realizes the miniaturization of the antenna: The GPR antenna designed by structure loading technology not only expands the work of traditional bow-tie antenna bandwidth,but also reduce the size of the antenna.It has better radiation characteristic curve and smaller antenna volume than ordinary bow-tie antenna;On the other hand,it enhances the directionality of the antenna: a metal shielded back cavity is added behind the drop-shaped antenna,and the interior is filled with absorbing material.In addition,a metal reflector is attached to the rear of the tripod antenna.As a result,the directionality and anti-interference ability of the two antennas is improved,which effectively reduces the radiation loss and weakens the direct wave effect between the transmitting and receiving antennas.The electromagnetic simulation software HFSS based on finite element method is used for modeling and optimization of two ultra-wideband antennas which combined with the actual application background.Among them,a drop-shaped antenna is taken as an example for actual testing and manufacture,and the stepped frequency ground penetrating radar(GPR)system is used to carry out experiments,achieve high-resolution detection of metal pipelines,and the application effect is good.The results show that the two antennas designed in this paper can effectively expand the bandwidth of the traditional bow-tie antenna,greatly improve the direction of the antenna,and it is easy to achieve impedance matching with the radio frequency wires.The antenna is small in size and has strong anti-interference ability,which is suitable for the ground-penetrating radar system to detect the distribution of pipelines in the shallow underground layer of the city. |
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