Design Of Parking Space Detection And Information Transmission Radar Front End

With the rapid development of China’s economy,the number of urban vehicles is increasing,and a variety of vehicle detection technologies have emerged.Compared with the traditional parking space vehicle detection technology,the Doppler radar detection technology proposed in this thesis had the advantages of high accuracy and was not easily affected by external environmental factors,so it had broad application prospects in outdoor parking lots.This paper focused on the design and implementation of power divider,power amplifier,mixer and transceiver antenna in the Doppler radar RF front-end circuit.The working frequency of the RF front-end was set to 2.45 GHz in the Bluetooth band(2.402GHz~2.485GHz),which facilitates the transmission and sharing of vehicle information with the baseband controller and link management layer.Firstly,in order to further broaden the bandwidth,reduce the volume and increase the gain,an inverted F-snake antenna is designed by bending method based on the analysis of the traditional inverted-F antenna.The simulation by electromagnetic simulation software HFSS showed: the working bandwidth ranged from 2.39 GHz to 2.52 GHz,the reflection coefficient S11 at 2.45 GHz was-29.91 dB,and the gain could reach 2.5dB.In order to meet the requirements of the RF frontend,one-two-division Wilkinson divider was designed.The insertion loss S21 and S31 of the two output ports at 2.45 GHz were-3.37 dB and-3.36 dB,respectively.The isolation S23 was-29.02 dB.According to the optimized inverted F-snake antenna and Wilkinson divider size parameters,the corresponding physical objects were fabricated and tested.The test results showed that the designed antenna and power divider meet the RF front-end performance requirements.Secondly,based on the comparative analysis of power amplifier and mixer,the corresponding power amplifier and single balanced mixer were designed according to the RF front-end indicators,and the simulation was carried out by the circuit simulation software ADS.The results showed that the saturation efficiency of the power amplifier at 2.45 GHz was over 59%,the saturation output power was above 38 dBm,and the gain was about 20 dB.The frequency of the RF input signal of the single-balanced mixer was 2.45 GHz,the frequency of the local oscillator input signal was 2.25 GHz,and the frequency of the intermediate frequency output signal was 200 MHz.When the local oscillator power was-6dBm and the RF power was-25 dBm,the conversion gain was 1.73 dB,and the 1dB compression point occurs between the RF input power was-16 dBm ~-15 dBm.In order to verify its performance,PCB layout design was carried out through the circuit and layout design software Altium Designer16,and the corresponding objects were produced accordingly.The measured results showed that the designed power amplifier test results were basically consistent with the simulation results.When the local oscillator power was-6dBm and the RF power was-25 dBm,the conversion gain of the test was-7.57 dB,which was 9.3dB lower than the simulation results,and a brief analysis of the error reason was given.At the end of the paper,transmission loss test and power test were carried out for the antenna transceiver system and the Doppler radar RF front-end system.When the transceiver antenna spacing was 40 mm,the transmission loss at 2.45 GHz was-45.98 dB,which provides a basis for the layout of the RF front-end transceiver antenna.When the arm was replaced by the vehicle and moved over the Doppler radar RF front-end system,the power received by the receiving antenna was-6dBm.As the distance between the RF system and the arm increased,the input signal power also increased.The measured data showed that when the detection distance was about 70 mm,the system had better detection performance in the range of input power from-30 dBm to-14.5dBm.Through circuit design,simulation analysis and actual test,the paper finally completed the RF front end system of Doppler radar,and gave the direction and distance of antenna layout and the farthest detection distance of parking vehicles.