| Recently,because of the increase in the number of private cars,traffic condition has become more and more complex,and the traffic accidents caused by vehicle lane changes have continued to rise.The Doppler millimeter-wave radar has high resolution,strong weather adaptability,small size,and is good at detecting moving targets.And It can effectively avoid unnecessary accidents caused by the driver's negligence,which has been wide attention by people.Although many domestic manufacturers have developed millimeter-wave radars,and 24 GHz millimeter-wave radars are relatively mature in the country,there are also many problems.For example,the millimeter-wave radar products of most domestic manufacturers use foreign chips,so Its maintainability is weak,and its hardware cost is high.Therefore,in order to address these issues,this article has independently developed a set of millimeter-wave radar system,using general components,from antenna to Radio Frequency(RF)to Intermediate Frequency(IF).The part of the RF uses the most basic analog device Field Effect Transistor(FET)to design,supplemented by some microstrip matching circuits,which can effectively reduce the cost of the radar and increase the repairability of the radar.The main contents of this article are as follows:Firstly,this article makes a brief introduction of the overall structure of a 24 GHz continuous-wave Doppler radar system.And then a miniaturized microstrip patch array antenna for 24 GHz radar is designed.Aiming at the unit that constitutes the entire antenna,the microstrip patch antenna,makes a details analysis and derivation of its principle.Then,according to the needs of the actual orientation pattern,a vertical polarization microstrip array antenna with narrow beams on the elevation plane and wide beams on the azimuth plane is designed,and its simulation parameters are given.Then,two-stage amplification is used to amplify the weak signal which is frequency reduction by mixer,and input it to the Microcontroller Unit(MCU)for Analog-to-Digital conversion and digital signal processing.The first stage of amplification uses a low-cost Triode to amplify.The second stage of amplification uses an integrated chip Operational Amplifier with better stability for amplification.Then,the phase and amplitude information of the target vehicle are extracted by the Microcontroller Unit.The reference level of the Operational Amplifier is set to about 3V,which is convenient for signal comparison.Because the power supply of general private cars is 12 V Direct Current(DC),and the MCU and Operational Amplifier chip use 5V DC power supply,a DC-DC circuit needs to be designed to perform voltage conversion.Lastly,the RF part of the millimeter wave radar is designed.Active RF devices which are difficulties and focuses of the RF section are analyzed and designed.Renesas' Field Effect Transistors working in the K-band are used to design a 12 GHz continuous-wave Oscillator,the simulation results are given.Then,the back-end is connected to a double frequency chip to output 24 GHz continuous-wave.The design of the entire millimeter-wave radar is summarized,and briefly introduces some changes which can be used in the research of other types of products.Briefly describes the method using this radar for distance measurement. |
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