Design Of Displacement Tag Radar System Based On CDMA

The construction of traffic and hydraulic engineering are the cornerstones to support the rapid development of social economy,the key factors to promote the happiness of local people,and important links to ensure the normal operation of the country.But the different degree of micro displacements of bridge,tunnel and hydraulic dams may occur under several external forces,such as earthquake,water,loose soil and internal stress within the structure.When such displacements exceed the safety limit,it may lead to collapse,which not only brings serious economic loss,but also threatens personal safety of the citizens.Therefore,the safety of large buildings is of vital importance.And the micro-displacement monitoring of the buildings should be placed in the primary position no matter during the construction period or after completion of operation.Aiming at the engineering application requirements of building safety monitoring and the defects that traditional instruments cannot automate multipoint real-time monitoring,a displacement label radar system based on CDMA is proposed in this paper.The basic principle of the displacement label radar system based on CDMA is to obtain the micro displacement of the target observation point by microwave phase interference.It uses CDMA technology to distinguish multiple observation targets.It is intended to solve the problem of multi-point measurement,achieve the purpose of automatic multi-point real-time monitoring,at the same time can improve the measurement accuracy and measurement distance of the system to a certain extent.The system is divided into two parts: displacement radar and displacement tag.The radar transmits radio frequency carrier signal,and the tag modulates it by spread spectrum.Then the radar amplifies the received signal,performs a series of operations such as orthogonal down conversion,filtering,and so on.After the digital signal is collected by the analog-to-digital converter,the code phase synchronization operation and despreading are carried out,and the displacement information carried by the despreading signal can be solved.Among them,the tag circuit uses microwave switch to realize the binary phase shift keying(BPSK)modulation of backscatter by switching different transmission paths,which simplifies the BPSK modulation circuit.The simulation program of the system is designed through Matlab platform,and the simulation results are analyzed to verify the feasibility of the system.The software of PN code generation and code phase synchronization is designed,and the correctness of the software function is verified by joint debugging using Matlab and Modelsim.The5.8GHz signal source is designed and manufactured,the experimental demonstration system is built,and the system test is carried out.The test results show that the displacement tag radar system based on CDMA can simultaneously observe multiple target points,and the displacement measurement accuracy can reach submillimeter level,which lays the foundation for the improvement of the system in the future.