Research On Borehole Logging Radar Pulse Source And Transmitting Antenna

In order to realize the accurate detection of geological conditions under complex conditions,it is necessary to develop detection equipment with superior performance.At present,the frequency domain microwave detection technology is widely used in the detection equipment.This technology is difficult to increase the detection distance while improving the resolution,which is greatly limited in the application of logging.Scholars put forward the contradiction between ultra wideband detection and high-frequency detection,which can fundamentally solve the problem of ultra wideband detection in the time domain.For the transmitter part of a borehole logging radar system,two kinds of pulse signal sources and transmitting antenna are developed,and good results are obtained in the actual test.Time domain pulse signal source is divided into unipolar pulse signal source and bipolar pulse signal source,which are analyzed and designed successively.Firstly,the working characteristics of avalanche transistor are described.Secondly,various topologies of pulse generation circuit are listed,and each order Gaussian pulse signal is analyzed.Based on these basic theories,the manufacture of unipolar pulse signal generation circuit is studied,the selection of various device models in the pulse generation circuit is discussed,the optimization effect of sharpening capacitor,shaping inductor,mica capacitor and other devices on the output waveform is studied,and a unipolar pulse signal generation circuit with a peak voltage of 432 V and a half peak pulse width of 1 ns at 10 k Hz repetition frequency is developed.Based on the unipolar pulse generation circuit,the bipolar pulse generation circuit is studied.The bipolar pulse generation methods such as differential method and pulse coupling method are listed.The traditional pulse coupling method is optimized,and a bipolar pulse signal generation circuit with peak to peak voltage of 691 V and peak to peak pulse width of 1 ns is developed under10 k Hz repetition frequency.In terms of transmitting antenna,firstly,the parameter indexes of UWB antenna are summarized.After comparing the advantages and disadvantages of various antennas,the half wave dipole antenna with simple structure and practical function is selected as the transmitting antenna of borehole logging radar system,and then the antenna is optimized by discrete resistance loading.The simulation shows that the S₁₁ parameters of the optimized antenna are less than-10 d B in the frequency band of 150 MHz to 1 GHz,The received waveform of the probe is highly consistent with the second-order Gaussian pulse signal.Then,the joint simulation of transceiver antenna is carried out with CST software.Through the simulation results,the distance between the antenna and the target is roughly the same as the actual distance.Finally,the integrated radiation experiment of monopolar pulse signal source and antenna and the combined radiation experiment of bipolar pulse signal source and antenna are carried out to explore the feasibility of miniaturization of borehole logging radar and verify the matching between bipolar pulse signal source and transmitting antenna.In terms of system test,the radar system pre-test and field test have been carried out successively.The prediction test proves the feasibility of the borehole logging radar system and evaluates the performance of the system.The field test verifies the stability of the radar system and completes the more accurate detection of the target.