| Ground penetrating radar (GPR) is a geophysical survey method that has been developed over the past thirty years for shallow, high-resolution, subsurface investigations of the Earth Structures. GPR uses high-frequency electromagnetic (EM) waves (generally 10 MHz to 1,000 MHz) to acquire subsurface information. When EM energy propagates downward the ground, it will be reflected back to the surface from boundaries of media with different dielectric constants. GPR has been proven to be an excellent tool for nondestructive evaluation and inspection of highway structures.; The objective of this dissertation is to design Giga-Flertz sampling systems for GPR applications. An introduction to GPR is given first. The operation of the sequential sampling method for pico-second sampling is described after that. Then sampling system design is divided into five parts according to the functions and the signal types of the circuit: the nano- and subnano-second pulse generator, the sampling circuit, the receiver circuit, the power supply and the amplification and attenuation circuit. In each part, circuit operation, design considerations, and circuit analysis are presented in detail. After that, the theoretical analysis of the system error and noise are derived. Based on the theoretical analysis, the possible noise sources in the system and possible methods to eliminate or reduce them are discussed. The lab test benches for debugging and testing the two kinds of sampling systems are built up and the field tests are conducted to test the performance of the system. The field test results show that these sampling systems are robust and accurate enough for the evaluation and inspection of highway structures. |
