Research And Design Of Microwave Radar Level Measurement

In recent years,with the rapid development of China's industrial technology and the acceleration of the automation process,the enterprises demand more and require highly for the level measuring instruments.With the unique advantages of non-contact,high measuring accuracy and low maintenance cost,the microwave radar level measurement technology has gradually become an important sensing means in the field of level measurement,with broad prospects.Firstly,the thesis introduces the development background,the research status of microwave radar and the basic principles of pulse ranging radar.Then a microwave radar level measurement system is designed according to the principles of vernier and correlation detection,and the ADS software is used to simulate and analyze the system.Then,ADS,CST,AD and other simulation softwares are used to conduct the circuit simulation and layout design of the transceiver antenna,oscillator,mixer,narrow pulse circuit,launch time detection circuit,filter and amplification circuit and other modules in the microwave radar level measurement system.In order to suppress the sidelobe level of the antenna effectively,two different feeding elements are used to realize the current distribution between the antenna elements in the same phase and different amplitude.Simultaneously,the series-parallel hybrid feeding network is adopted to ensure the antenna bandwidth and reduce the loss.The measured results show that the array antenna bandwidth is 690 MHz(23.77-24.46 GHz),the maximum gain can reach 20.1 d Bi,and the side-lobe level of plane E and plane H is-20.7 d B and-19.3 d B,respectively,which meet the design requirements of microwave radar level measurement system.In order to improve the output power of the oscillator,based on the principle of parallel feedback oscillator,this paper adopts the microstrip ring structure and the microstrip coupling line as the frequency selection network,and adopts the heterojunction field effect transistor(HJ-FET)NE3514S02 of NEC as the amplifier unit to design a high output power oscillator.With continuously optimizing and tuning as well as many physical debugging,the center frequency of the oscillator is 24.37 GHz and the output power is 6.25 d Bm,indicating that the frequency deviation of the oscillator is within the allowable range of error and the output power meets the design requirements of the system.In order to realize the narrow-pulse needed by the system,this paper designs the narrow-pulse circuit by using the function of D flip-flop rising edge triggering and clearing,as well as the transmission delay of the logic device itself.The test results show that the pulse width of the main pulse is 15 ns,the pulse repetition frequency is 3.686440 MHz,and the pulse amplitude is 5 V,the pulse width of the vernier pulse is 15 ns,the pulse repetition frequency is 3.686400 MHz,and the pulse amplitude is 5 V,which basically meet the design requirements of the system.Finally,the designed microwave radar level measurement system is used to measure the level of close range targets in the microwave laboratory and the results show that the system can accurately measure targets within the level of 1?3 m,with the measurement accuracy reaching ±10 cm.