Design And Implementation Of Displacement Radar Transponder

Large structures,such as transmission tower,reservoir dams and skyscrapers,deformation and displacement are easy to occur during use,especially in the disaster.It is necessary to study effective deformation monitoring methods and deformation monitoring instruments in order to diagnose the quality of the project and predict the possible disasters.Compared with the optical displacement measurement system,the microwave displacement measurement system has the advantages of all-weather,high-accuracy and automation.In the support of Chongqing Science and Technology Project "the Radio Monitoring Technology of the Critical Rock and the Micro-deformation of Large Buildings" and "the Triple Channel and its Application in Micro-displacement Measurement",the research group has applied for the invention patent "A Micro-displacement Measurement System" and developed the corresponding experimental system.The basic principles of this system are as follow:placing the passive corner reflector at the measured point and the displacement measurement radar at the measuring point,the displacement measurement radar radiates the RF carrier signal to the corner reflector,and the passive corner reflector returns the RF carrier signal directly along the original path.The phase difference between the received signal and the transmitted signal can be calculated by the displacement measurement radar and deformation amount can also be obtained,the measurement accuracy can reach sub-millimeter level.The problems in actual use are as follow :(1)the measurement distance of the radar is directly related to the size of the corner reflector,and the size of the corner reflector is too large to make the installation inconvenient;(2)The corner reflector can only reflect the RF signal,without signal processing ability,this system cannot realize multi-point measurement.In view of these problems,in the support of National Natural Science Fund Project "Micro-deformation Monitoring Radar Technology Research" and the Chongqing Science and Technology Project "Research on Displacement Label Radar Measurement Technology",the research group has applied for the invention patent "A Multi-target Micro-deformation Real-time Telemetry Method and System" and developed the corresponding experiment system.The basic principles of this system are as follow:the displacement radar transponder is installed at the measured point(replace the passive corner reflector)and the displacement measurement radar is placed at the measuring point,displacement measurement radar launches RF carrier signal to displacement radar transponder,the displacement radar transponder modulates the received RF carrier signal with sinusoidal modulation signals of different frequencies and then forward it back.the displacement measurement radar receives the mixed echo signal of multiple displacement radar transponders,signal separation algorithm is used to distinguish these signals.Calculating the RF carrier phase difference between the carrier and each radar transponder can obtain every carrier's relative displacement.This system has the following advantages:(1)By adjusting the power of transmitted signal from the transponder of the displacement radar,the measurement distance can be effectively increased,long-distance measurement can be realized,and the transponder can also be made very small and easy to install and use;(2)Each displacement radar transponder has adjustable parameters,different frequencies and make this system has multi-point measurement capability.This thesis mainly completes the design and implementation of displacement radar transponder.The displacement radar transponder is divided into three parts of a modulation signal generation module,a reception module and a transmission module.The circuit schematic of each module and the hardware circuit diagram of PCB are respectively designed.(1)The modulation signal generation module generates a sine wave signal with adjustable parameters.In order to improve the quality of the output modulation signal,a phase locked loop frequency multiplication circuit is designed to multiply low-frequency signals to high frequencies as the input reference clock of the DDS module,multi-stage filter circuit and power amplifier circuit are designed at the output end.(2)Multi-stage filter circuit and Multi-stage low noise amplifier circuit are designed in the receiving module to filter and amplify the received RF carrier signal,use a narrow-band cavity filter to achieve frequency isolation of transmit and receive signals,design power division circuit to divide the RF carrier signal into two channels.The detection circuit and the analog-to-digital conversion circuit converts one of the signals into a digital level.A multi-stage adjustable digital stepping attenuation circuit and a multi-stage power amplification circuit are designed to dynamically adjust the power of the other signal.In order to improve the practicality of displacement radar transponder,microwave switch circuit is designed to select transponder RF carrier signal source.(3)The transmitter module design mixer circuit mixes the sine wave modulation signal and the RF carrier signal.The microwave switch circuit is designedto achieve the manual or automatic control of the attenuation of the digital stepping attenuation circuit.The power division circuit divides the transmit signal into two channels.Each channel signal is designed with power amplifier circuit and band-pass filter circuit respectively,and the narrow-band cavity filter with different center frequency is designed to filter.Finally,the combiner circuit is designed to synthesize the signal and use the transmitting antenna to radiate to the displacement measurement radar.The displacement radar transponder were tested with a spectrum analyzer and a high-frequency signal source.The verification results are as follow:the displacement radar transponder can effectively receive the 5800 MHz RF carrier signal with a receiving sensitivity of-70 dBm.The IF signal frequency is 190 MHz,displacement radar transponder output 5610 MHz and 5990 MHz two frequency components,the power of the 5610 MHz signal is 8dBm and the power of the 5990 MHz signal is 5dBm.