Optimization Design And Implementation Of UWB Antenna For Borehole Radar

With the development of economy,mankind's demand for fossil energy is further enhanced,which makes mankind continuously explore the advanced technology suitable for the exploration and development of underground resources.Borehole Radar(BHR)is a new and efficient geophysical exploration tool.It transmits transient pulse signals to the Borehole formation through transmitting antenna.When the electromagnetic pulse meets the media with different electrical parameters,it will be reflected.As the transceiver component of the borehole radar system,the borehole radar antenna is mostly ultrawideband time domain antenna.Its performance directly affects the detection performance of the borehole radar system.However,due to the limitation of borehole size,conventional UWB time domain antenna is not suitable for borehole radar antenna in various engineering applications.At the same time,the complex environmental conditions are also the key factors that restrict the performance of the radar system in the well.Oil and gas exploration Wells are usually filled with mud with high conductivity and high dielectric constant.The antenna in the mud hole often results in impedance mismatch,low radiation efficiency and even can not work normally due to the influence of mud electrical parameters.Therefore,on the premise of meeting the requirements of borehole size and the constraints of complex mud environment,it is difficult to design the UWB antenna for radar in borehole with excellent time domain performance parameters.To solve the above problems,this thesis analyzes and studies the structure of resistive-loaded dipole antenna commonly used for radar in borehole,and designs two kinds of printed dipole ultra-wideband omnidirectional antenna for radar in borehole,which can greatly improve the radiation efficiency and gain.The design of ultra-wideband directional antenna for radar in low profile well is completed.The main research contents of this thesis are as follows:1.Explores the resistive dipole electric size and antenna radiation efficiency,gain,and the relationship between the fidelity,and from two angles of time domain and frequency domain analysis,we design a structure of bending resistance load ultrawideband omnidirectional dipole antenna,in meet radiation pulse waveform under the premise of high fidelity,a sharp rise in the antenna's radiation efficiency and gain.2.Based on the resistance loaded dipole antenna with bent structure,a kind of mixed resistance and capacitance loaded dipole ultra-wideband antenna is designed according to the characteristics of "phase leading",which further improves the radiation efficiency and gain,and has good fidelity.The impedance matching of the antenna in different media is analyzed,and its S parameters and pulse waveform are tested.3.This thesis proposes a design idea of ultra-wideband directional antenna for radar in borehole,which works close to the borehole wall.While making the radar antenna in borehole get directionality,the influence of mud on antenna performance is basically avoided,and the high performance of radar directional antenna in borehole is realized in complex mud environment.