The Circuit Design Of GPR's Transmitter And Receiver Based On DDS

Direct digital frequency synthesis (DDS) is a relatively new method of frequency synthesis,it is an all-digital frequency synthesis which used Nyquist sampling theorem to make a series of digital signals into analog signals by means of DAC and widely used in radar, navigation, and instrumentation and other equipments as reference clock and standard signal source. This article describes the use of DDS as the signal source which is applied to GPR.GPR is an effective nondestructive dectection of shallow physical techniques which is developed in recent years and being extensively studied, it uses the reflection of high frequency electromagnetic waves of 1M-1GHz to detect the objective and geological structure. Compared with the traditional geophysical methods,GPR has the advantages such as the continuous detection, real-time display and so on.SFR is a kind of GPR system whose transmit and receive signals are all frequency-domain signals and can be convenient to use frequency domain signal processing techniques to process and analyze the target echo signals. Different GPR requires the signal source which shoud meets to its own characteristics, the stepped frequency signal source is an important indicator to measure the performance of SFR, high accuracy, high stability of the signal source play a vital role in the radar.The article mainly introduces the stepped source for SFR and designes the stepped frequency system which is based on DDS;then it designes the gain and phase detection of receiving as well as the data acquisition system.The article discusses the basic theories of GPR and DDS,then produces the stepped signal which uses DDS in the control of AT89S51,and a theoretical analysis about DDS spurious is given then uses Matlab and Multisim10 to analyz different filters'features and so an elliptical lowpass filter is designed to reduce this spurious, at the same time,the gain and phase detection circuit is designed which is based on AD8302 to detect the transmit and echo signals, it uses C8051F020 as a whole controller to realize the data acquisition, storage and communicate with PC, and verify the detection of AD8302 and the validity of data acquisition ,finally complete the software and hardware design and debugging.