Research On Receiving Front-end And Signal Processing Technology Of Time-domain Logging Imaging Radar

Due to its extremely narrow pulse signal with high peak value and high repetition frequency,time-domain radar has strong anti-interference ability and the ability to penetrate the medium.And it’s the reason that why time-domain radar has excellent performance in the application scenario of logging imaging.As the core part of the time domain imaging radar,the receiving front-end and the signal processing technology of the echo signal determine the performance of the time domain imaging radar,which has important research significance.Based on the mentioned situation,this thesis has carried out investigations on the receiving front-end and signal processing technology of time-domain imaging radar,which can be stated as follows:First of all,this thesis studies the sampling method of time-domain imaging radar,adopts a method of combining sequential equivalent sampling with time interleaving technology,and uses a four-channel equivalent sampling method to sample high-frequency time-domain signals.In order to realize this sampling method,two kinds of delay chips,which are programmed and controlled by a field programmable gate array(FPGA)development board,are combined to generate a large range of high-precision delay pulse signals.At the same time,FPGA is also used to control an analog-to-digital converter(ADC)device to collect the echo signal,and to eliminate the bad points and reconstruct the sequence of the collected data.To meet the requirements of ADC devices,an analog front-end circuit is designed to preprocess the echo signal.The feasibility of the receiving front-end is verified by comparing with the signal collected by the oscilloscope.Secondly,this thesis studies the signal processing technology of time domain logging imaging radar from three aspects: migration removal,noise suppression,and depth gain compensation.The calibration and normalization are completed in two directions of time and amplitude,eliminating the problem of signal jitter caused by the transmission signal in the process of generation.Aiming at the random noise in the process of signal reflection and the direct wave between the receiving and transmitting antennas,data accumulation and out-of-band noise filtering are carried out to reduce the clutter interference.The gain compensation of the signal according to the propagation distance makes up for the energy attenuation caused by the propagation process.After simulation experiment,the effectiveness of the above signal processing technology is proved with grayscale image of the target signal.At last,the whole experiment of receiving front-end and signal processing technology is carried out.The echo signal of time-domain imaging radar is collected by the receiving front-end,and the collected data is uploaded to the computer for signal processing.It is shown that the reception front-end and signal processing technology designed in this thesis are well connected and can produce good results.