| The attenuation of millimeter-wave signal during transmission is lower than that of infrared and laser.Millimeter-wave detection system has higher detection capability than traditional infrared detection system in such complex environments as rain,fog and smoke.As the core of millimeter wave detection system,millimeter-wave radiometer has the advantages of simple structure,good anti-interference ability and strong penetrating power.It has been widely used in many fields such as intelligent ammunition,weather forecast,astronomical observation,agricultural production assessment,environmental monitoring and hazard detection.As an indispensable device of millimeter-wave radiometer,millimeter-wave low noise amplifier can amplify high frequency signal received by the antenna,it can effectively suppress the noise of the amplification process and improve the performance of the radiometer receiving system.This paper designed a 8mm band radiometer low noise amplifier adopts tertiary cascade amplification structure,the first stage amplifier uses the minimum noise matching design,it can ensure that the low noise amplifier has the minimum noise factor,second stage and third stage amplifier uses a maximum gain matching design,it can guarantee the overall gain of low noise amplifier.Then the amplifier's micro-strip bias network is designed separately to ensure the stability of the amplifier.The simulation results of ADS show that the noise coefficient of the designed LNA is 1.7dB,and the gain of the system reaches 35 dB,which satisfies the design requirements of the radiometer.The millimeter-wave mixer is the frequency conversion device of the radiometer system,it can convert the received RF signal into a more easily processed medium frequency signal.In order to overcome the difficulty of designing and manufacturing high frequency local oscillator,this paper adopts the four-harmonic mixing method to reduce the required local oscillator frequency to 1/4 of the original,which greatly reduces the design difficulty of millimeter-wave mixer.Harmonic mixer RF input frequency is 34.5GHz,the local oscillator frequency is 8.6GHz,intermediate frequency output is 100 MHz,its main body adopts the reverse parallel diode structure.In order to reduce the conversion loss of the mixing process,this paper designs the harmonic reflection micro-strip line,the IF low pass filter,the LO low pass filter and the RF band-pass filter.It effectively reduces the leakage of the local oscillator,improves the utilization of harmonic energy and the isolation between each port.The simulation results show that the frequency conversion loss of the mixer is 11 dB,and the port isolation between each port is more than 20 dB,and the mixer design requirements are achieved. |
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