Design And Realization Of The Transceiver Circuit Of Stepped Frequency Ground Penetrating Radar In VHF Band

With the rapid development of our country's economy and the enhancement of comprehensive national strength,underground detection has received more and more attention.As a more practical detection equipment,ground penetrating radar has the advantages of no damage to detected objects,fast detection speed,and continuous imaging.It has received extensive attention and research.The application range of ground penetrating radar is quite wide.It can be used for engineering quality supervision,mining,underground survey and military demining,etc.It plays a very important role in the process of promoting economic development and in the military.Therefore,it is necessary to strengthen the research on ground-penetrating radar and continuously improve the performance of ground-penetrating radar in order to better exert its practical value.This article first introduces the research background and significance of ground penetrating radar,and expounds the research trends of ground penetrating radar at home and abroad.Then the ranging principle of the stepped frequency ground penetrating radar is introduced and the parameter analysis of the transmitter is carried out.On this basis,the selection of the step frequency range and the step length is carried out,and the technical indicators of the receiver are explained.The design plan of this system was explained in detail later,including the composition of the transmitter,the composition of the receiver,the composition of the FPGA control part,and the writing of the chip driver.Finally,the whole hardware part is tested and analyzed.The transmitter contains a DDS and gain control section.FPGA controls the DDS chip AD9912 to generate a continuous wave signal with a step frequency of 60MHz-180 MHz in the VHF frequency band,and the step length is 2MHz.Then use the gain control part to adjust the transmitter's transmit signal power and power flatness.The receiver consists of low noise amplifier PSA-545,quadrature mixer AD8348 and analogto-digital conversion chip AD7729.The low noise amplifier provides a fixed gain of 20 d B for the signal entering the system,and the quadrature mixer provides a dynamic gain of44 d B.The step frequency echo signal passes through the low noise amplifier and enters the quadrature mixer for self-mixing.After being filtered by the RC low-pass filter,the beat signal is generated.The beat signal enters the AD7729 for analog-to-digital conversion,changing from an analog signal to a digital signal.After that the signal is passed to the FPGA.The FPGA control part takes a Xilink Spartan-6 series chip as the core,and builds Flash and crystal oscillator circuits for it to configure the transmitter and receiver chips.The writing part of the driver introduces in detail the programming idea of AD9912 to generate step frequency signal,the register configuration of AD7729 and the realization method of data transmission to PC.The results obtained through the hardware test: the transmitter realizes the transmission of a signal with a step frequency of 60MHz-180 MHz with a step size of2 MHz,and the power flatness is controlled within the range of 2d B,and the receiver can self-mix the received signal The beat signal is generated by frequency and converted into a digital signal by ADC and sent to FPGA to complete the system's transceiver function.Then the data is transferred to the PC,the basic ranging function is completed after analysis and processing by Matlab software.