Development Of Low Frequency Ground Penetrating Radar Receiver

Ground Penetrating Radar (GPR), as a geophysical method, is widely applied in thenondestructive detection of underground target. GPR systems are generally designed forspecific use to ensure good detection accuracy, due to the complexity of ground-mediumelectromagnetic characteristics and the differences in target reflection characteristics. Inorder to detect flammable ice under permafrost in Qinghai, the detecting signal of GRPneeds to reach the depth of more than130meters in that region. Current GPR systems,however, are mostly used to detect targets from several centrimeters to50meters in depth,with the antenna center frequency in the range of10MHz to4GHz. Improving thepenetrating capability of radar wave is one way to achieve the investigation depth, andcompensating the return wave also helps. This paper focuses on the receiver design inGPR system, and the main content is as followed.System analysis and overall design. Firstly, research and analyze the detectionprinciple of GPR system and receiver design requirements. After comparing the bothsides of different GPR types, impulse GPR is chosen for its suitability for field detection.Then the design indexes as well as the hardware design scheme is determined based ontheoretical analysis and empirical formulas. The design is an internal synchronized real-time GPR reciever with time-varying gain function.Implementation of the designed reciever. The implementation can be divided into3parts, hardware circuits, FPGA control logic and upper computer software. According tothe functional design requirements, hardware circuits mainly comprise sampling triggercircuit, time-variable gain circuit, ADC sampling circuit and data transmission circuit.FPGA control logic, corresponding to each part of the function circuits, consists of4modules. It is designed with ISE Foundation software. The communication betweenreceiver and upper computer is through Universal Serial Bus. The software compiled withLabVIEW can realize the function of data reception, data and wave display, data storage,and continuous stepped gain setting.Function verification and performance test. All designed function has been verifiedand performance parameters have been tested, including noise figure, sensitivity,bandwidth and dynamic range. The test results show that the design can meet thefunctional requirements and its performance is good. Compared with traditional impulseGPR receivers, this design can make an efficient use of signal energy and enlarge dynamicrange effectively. Besides, internal synchronization can avoid interference caused by movement of the sync cable.