Research And Design Of Transmitter And Receiver Circuit Of Ground Penetrating Radar

Ground penetrating radar(GPR)is a widely used non-destructive geophysical survey technology.It detects underground targets and geological phenomena based on that transmission and reflection of electromagnetic waves will appear in discontinuous underground media.This technology has been increasingly used in engineering practice as well as in urban pipeline detection,mineral exploration,life rescue detection and some related scenarios.It is necessary to learn more and explore further on the high-perfomance transceiver circuit of ground penetrating radar as the result of the increasing demands for the accuracy and depth of ground penetrating radar in our society.This thesis mainly studies the design and implementation of ultrawide band(UWB)pulse ground penetrating radar transceiver circuit.By comparing and analyzing the various implementation schemes of transmitters and receivers,a digital pluse GPR transmitter is proposed,which has the advantages of strong reusability and easily adjusted parameters;a real-time sampling receiver is also proposed.A high-speed DAC is used as pulse generator,cooperated with front-end analog circuits such as attenuator and amplifier in this GPR transmitter.Meanwhile,based on high-speed ADC,a real-time sampling receiver with high sampling rate and high dynamic range is designed as well.The main work of this thesis is as follows: Firstly,this thesis investigates and compares the existing research within domestic and without,summarizes the development direction and trend of GPR technology currently,and analyses several significant types of GPR.Then,the basic theory of ground penetrating radar technology is introduced in detail,the propagation characteristics of electromagnetic wave,especially pulse electromagnetic wave in underground medium are studied.The system structure of ground penetrating radar transceiver circuit is designed as well.Secondly,the traditional technology scheme of step recovery diode and avalanche transistor as the UWB pulse generators are investigated,their typical circuits are simulated and measured at the same time.Based on those limitations,a new type of pulse variable ground penetrating radar transmitter with high-speed DAC as core,a high-performance FPGA as main controller,and RF front-ends such as amplifier and attenuator is desiged,which is able to generate the pulse that its width,repetition frequency and amplitude can be adjusted individually.The high gain wideband antennas are designed simultaneously.After studying the implementation of the traditional UWB radar receiver,the high-speed ADC is chosen as the core of the receiver,and in corporation with analog signal front-end circuit such as peripheral filters,amplifiers and attenuators,a new type of ground GPR receiver with high dynamic range and high sampling rate is proposed and realized accordingly.Finally,according to the designing methods in this thesis,the transmitter and receiver circuits are fabricated and tested carefully.This transmitter could generate pulse signals with the narrowest time width at 1.8ns,the highest voltage at 12.7V,and the repetition frequency reaches 100 MHz.The sampling rate of the receiver could achieve 1000 MHz,and the dynamic range is up to 48 dB.A comprehensive experiment of transmitter and receiver circuit has been carried out,and its ability of underground target detection are verified accordingly.The test results show that the design and debugging of the transmitter and receiver circuits of GPR proposed in this thesis have been completed successfully.Moreover,the pulse variable GPR transmitter and receiver circuit proposed in this thesis has the characteristics of highly integrated,easily adjusted parameters,expansibility and so on.