Fiber Optic Transmission Technology Is A New Application In Ground Penetrating Radar System Design

Ground Penetrating Radar (GPR) is a geophysical prospecting method by using reflection of high-frequency electromagnetic wave to detect target and underground medium distribution. Since the pulse generated by the impulse ground penetrating radar has a plenty of low and high frequency components, the impulse ground penetrating radar can balance the system performance of the detecting range and resolution, and therefore it has been widely used to detect and identify the targets in the multiple-scattering environments such as forest, snow, soil, and so on.Due to the sharp pulse generated by the impulse ground penetrating radar has widely instantaneous bandwidth, it is very difficult to achieve undistorted and dispersion-free transmission by coaxial cable. If the light wave as the narrow pulse signal carrier, the relative bandwidth of pulse transmission can be effectively reduced; And optical fiber is made of insulating material, will not arise the problem of waveform distortion caused by the radiation of the charged cable sheath. So optical fiber instead of coaxial cable as the signal transmission medium of the impulse ground penetrating radar has important engineering significance.The main works of this dissertation are to design and optimize the optical fiber transmission system fit the requirements of the impulse ground penetrating radar, according to the especial demands of the GPR signal transmission system.The main contents and innovations of the dissertation are summarized as follows:(1) Optical fiber transmission system,which based on the analysis in the non-carrier, large instantaneous bandwidth Gaussian pulse signal is used in radar signal transmission;(2) A suitable scheme of the impulse ground penetrating radar signal transmission which based on the combination of optical fiber communication principle and performance parameters of photoelectric device is designed;(3) Analog optical transmitter module designed with digital laser driver chip is achieved, and the slow start circuit, automatic power control circuit (APC) are used to ensure stable operation of the transmitter module; (4) Two sets of signal reception designs by using different photoelectronic detection devices and related chips is completed, and the advantages and disadvantages from the analysis of principles and measured data are compared, thus the optimum design is achieved;(5) The modulation circuit and impedance matching circuit to fit the narrow pulse signal is designed, and linear signal transmission in the test of the impulse ground penetrating radar signal transmission is achieved.