Research On Tr Front-End Of Borehole Radar System

The research of borehole radar system has the strategical significance for the mineral resource detection and underground exploration.This thesis mainly focused on key technologies for the design of borehole detecting system based on impulse radar,described the characteristics and key performance of borehole radar system;developed petroleum drilling radar impulse signal pulse source,time variable attenuated RF receiver module and radar imaging algorithm in petroleum drilling exploration.Development of low jitter impulse signal source.Several common UWB signal generation method,mathematical form,and spectrum analysis are discussed;Gauss signal in attenuation and propagation characteristics of geology is analyzed,CST simulation results of the first-order Gauss signal in geology of target scattering characteristics are proposed;finally a mathematical model to determine the impulse signal source of radar system is given.Based on the avalanche effect of avalanche transistor,the working mechanism of avalanche circuit and the dynamic transformation of operating point,a low jitter pulse signal source is developed on the basis of Marx circuit.Through out the theoretical calculation of the Marx circuit and using Orcad simulation,the Marx circuit is optimized to achieve a better performance.The driver circuit is designed by using the isolation circuit and the avalanche transistor to reduce the trigger jitter.By selecting the avalanche transistor FMMT415 and the avalanche crystal diode P4SMA540 A,the peak value of the impulse signal source is 690 V,the half peak pulse width is about 500 ps and the trigger jitter is about 32 ps.Development of RF receiver front end with time-varying attenuator;Based on the analysis of the transmission characteristics and the reflection characteristics of the target,the characteristics of the system are calculated.This paper presents the development of time-varying attenuation circuit and low noise factor link with MA4P7455 to increase the dynamic range and the sensitivity of the receiver,and reasonably allocate the whole receiver's parameters by optimized using ADS simulating software.The control signal of the time-varying attenuation circuit is generated by a bootstrap circuit and a triangular wave circuit designed by a voltage follower,and the triangular wave circuit achieves an adjustable rise time of 50 ns-2 us.The working bandwidth of the RF receiver is 30 MHz-1 GHz,the gain dynamic range is about-15 dB to 53 dB,the noise figure of the gain module is 0.82 dB,the noise figure of module is 3.6dB and the system sensitivity is-83.59 d Bm.In the scattering experiment of the target,the spectrum of the reflected signal of the target is is mainly distributes between 300 MHz-800 MHz.At the same time,the use of time-varyingamplification,correlation function,median filtering method can effectively suppress the clutter;the use of median filtering method can also depress background signals,effectively solve the radar moving target imaging.