Radar For Water Level And Flow Rate Research

The hydrological monitoring of rivers, lakes and oceans is important for production and living of people. Water level and flow rate are two most important parameters in hydrological monitoring. As the water level and flow rate measuring device, the radar for water level and flow rate has the incomparable advantage over other measuring instruments so that the development of high precision, low cost of water level and flow rate radar has great significance.According to the demand of engineering, starting from the theory of radar measuring range and speed, this thesis puts forward the radar parameters, made the overall scheme of radar and the feasibility analysis. This thesis develops a radar which has functions of measuring water level and flow rate by switch. This radar can be divided into two parts, RF front-end system and the signal processing system. RF front-end system mainly includes signal source, launch branch, receive branch, IF filter circuit and the automatic gain control circuit(AGC). This radar uses different launch signals to realize water level and flow rate measurement, water level measurement with 11.5 ~ 12.5 GHz triangle wave linear frequency modulation continuous wave(LFMCW) and the flow rate measurement with 12 GHz single-rate continuous signal. Signal source which uses the “DDS + PLL” scheme not only can achieve wide band, high linearity, but also is easy to realize different waveforms switching.Signal processing system mainly includes single-ended-to-differential circuit, ADC sampling, the Angle measuring module, memory module and serial interface communication module and so on. In the measurement of difference frequency signal, the variable frequency sampling scheme is adopted, which difference frequency signal can be divided into different band and different frequency bands are corresponding to the different sampling frequency. As a result, the frequency measurement error of the difference frequency signal meets the system requirements under the condition of FPGA resources limited.According to overall scheme of radar, this thesis designs each circuit module, including the “DDS + PLL” circuit, hairpin band-pass filter, power amplifier, power divider, circulator, LNA, mixer, IF filter, AGC circuit, single-ended-to-differential circuit, Angle measuring circuit, serial communication circuit, FPGA minimum system, etc. Upon the completion of the hardware production, the RF front-end system and the signal processing system are debugged separately, then the overall test of radar is simulated by putting them together with cable and antenna. Test results show that this radar not only implement the function of water level and flow rate measurement, but also has 10 mm and 0.3 m/s performance in terms of accuracy and meets the expected target.