Radar Sensor For Water Level And Flow Rate Research

In the hydrological monitoring for the environment such as rivers, lakes and oceans,the water level and flow rate are two important monitoring contents. Designing moreaccurate and convenient measuring instruments for water level and flow rate hasimportant significance. As one kind of water level and flow rate measuring instruments,the radar water level and flow rate sensor has a unique advantage compared with othermeasuring equipments. The radar water level and flow rate sensor is a microwavemeasuring radar. Transceiver system is an important part of the radar and plays adecisive role for the overall performance of the radar. Designing low-cost, small sizeand high stability of the transceiver system has important significance.According to actual needs, the thesis develops a radar front-end which has themeasuring function of water level and flow rate. The front-end consists of receiving andtransmitting channels, including microwave signal source, RF transmitting branch, RFreceiving branch and IF processing circuit. For measuring water level and flow rate, thesystem uses different transmitting waveforms to be switched by a switch. The waterlevel is measured with a frequency of11.5GHz-12.5GHz linear frequency modulatedcontinuous wave (LFMCW), and the flow rate is measured with a frequency of12GHzsingle-frequency signal. The microwave signal source uses the “DDS+PLL” scheme.The DDS chip is controlled by a microcontroller and it can easily be switched betweenthe different waveform patterns. The transmitter and receiver share a common antennawith the circulator to achieving isolation and it is conducive to miniaturization of radar.In the process of the research, starting from the theory, the thesis develops thegeneral scheme of the system and determines the important parameters of the system. Itis also verified by the overall simulation and feasibility analysis of the program. Thisthesis also discusses the designing for each unit circuit, including the DDS chipcontrolling circuit, the PLL circuit, the microwave filter, the power splitter, the poweramplifier, the circulator, the low-noise amplifier, the mixer, the IF processing moduleand the power supply circuit. The system has both digital circuits and analog circuits. Inorder to prevent the crosstalk of signals between the digital circuit, analog circuit, as well as the RF circuit, also in order to prevent external electromagnetic interference, thesystem uses the separated cavities for isolation. Each unit circuit is independentlyplaced in a cavity to reduce interference and improve system performance.In the last, each unit circuit and the cavity is processed and assembled. Severalmajor unit circuit and the entire transceiver system is tested. The thesis analyzes theproblems encountered in the process of debugging and test results. It also put forwardsuggestions for improvement, and lay the foundation for further development work.