| This thesis is focused on the research of Time domain ultra wideband antennaapplied in petroleum exploration borehole radar system. Four subjects are discussed,including the transmission property of the electromagnetic pulse in borehole, the designof borehole radar transceiver antennas, the study of the impedance matching betweenthe antenna and the pulse generator in impulse based directional borehole radar, theexperiment test of the designed antenna and analysis the imaging results.As for the transmission property of the electromagnetic pulse in borehole, twoworks are reported. Firstly, the influencing factors when electromagnetic pulsespreading in borehole are discussed, especially, the effects of the dielectric constant,conductivity and frequency on radar detection distance. Secondly, some investigates arecarried out about the influence of the HE11mode on radar detection and imaging.As for the design of borehole radar antenna, five works are carried out. Firstly,aimed at the Project metrics, the transceiver antenna program is proposed. Secondly, aresistively loaded omnidirectional dipole transmitting antenna is designed, with the helpof electromagnetic simulation software, CST and ADS, the design achieve the optimalsolutions. Thirdly, a compact ferrite based directional antenna with center frequency at100MHz and be employed for radiating Gaussian monocycle pulse with peak–peakwidth of3ns has been designed. The parameters of the antenna are with2.5:1front to back ratio,±60°directional diagrams at half peak amplitude. The dimensions ofthe antenna is48×54×440mm. Fourthly, in order to the miniaturization of radarsystem and farther detection distance, a compact lumped loading cylindrical conformaldirectional monopole antenna with68mm diameter and185mm height has beendesigned. The antenna is employed for radiating Gaussian monocycle pulse withpeak–peak width of1.5ns. The parameters of the antenna are with about5:1front to back ratio in the amplitude scale,±90°directivity patterns at H plane at halfpeak amplitude. The experimental results of the three antennas all are in goodagreement with the simulation results provided by the commercial software (CSTMWS). As for solving the impedance mismatching between the antenna and the pulsegenerator in impulse based directional borehole radar system, two works are carried out.First of all, a field experiment was conducted to verify the cause of reflection signalproducing. And then, a simple and effective ultra wideband impedance matchingapproach is proposed to solve the impedance mismatching between the antenna and thepulse generator, experiment result indicates that the proposed method is simple andeffective for solving the ultra wideband impedance matching in impulse based boreholeradar system.As for the experiment test of the designed antenna and analysis the imaging results,three works are carried out. First of all, a new scheme of directional borehole radar isproposed. Secondly, a field experiment is carried out to study the time domaincharacteristic of the antenna in Simulated well. Finally, a field experiment is carried outin Real oil borehole. The experiment results indicate that the proposed directionalborehole radar system is a good candidate for the borehole detection application. |
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