Design And Implementation Of Receiver RF Front-end For S-band Wave Radar

The rapid development of electronic technology promotes the application of remote sensing on ocean monitoring area.The Radio Ocean Remote Sensing Lab of Wuhan University has developed an S-band Doppler wave radar system named MORSE.MORSE adopts the coherent wave measuring method which frees the radar from calibration.Thus,MORSE is more adaptive and convenient.In wave radar system,the RF receiving front-end is right after the antenna,which is the crucial part.And its performance is directly relative to the radar's proper functioning.Besides,the trend of small-size radar also requires a highly integrated,low-power-consumption RF receiving front-end.So it is of great significant meaning that a RF receiving front-end meeting the needs of MORSE is designed,assembled and applied.Under that background,some typical receiver structures are proposed in this thesis and their pros and cons are discussed.Some solutions are also listed.Then the key parameters of the receiver are introduced.According to the demands of MORSE,the basic structure of the RF receiving front-end is determined as superheterodyne with two downconversion.The whole circuitry is divided into five parts: the RF part,the first IF part,the second IF part and two LO parts.Based on the characteristics of the circuit parts,the signal chains are analyzed and designed and the key devices are chosen.After that,the feasibility analysis is done and the theoretical value of gain,noise figure,sensitivity and linear dynamic range is calculated and ensured to match the demands.The detailed design is then conducted and the PCB layout is performed to finish the board level circuit design.To ensure the proper function of the circuit,the simulation of the amplitude-frequency response of the signal line on the PCB is done with the SIWave in the Ansys Electromagnetic Suite.And the shield box is also designed with Solidworks and the electromagnetic field distribution as well as the resonance frequency of the box is also calculated with Electronics Desktop in the Ansys Electromagnetic Suite to ensure the shielding effectiveness.After the assembly,the crucial process of the circuit tuning is discussed in this thesis.Detailed analysis and feasible solutions are proposed and validated.A comprehensive measurement regarding the performance of the RF receiving front-end is conducted after circuit tuning.The results of power consumption,input/output bandwidth,sensitivity,input 1dB compression point,linear dynamic range,gain,noise figure,T/R isolation,image rejection ratio,variable gain,output signal-spur ratio are listed.And a close loop test is performed and the results is illustrated.From the results,a conclusion can be drawn that the overall performance of the RF receiving front-end is good.The front-end successfully maintains a relatively small noise figure,high dynamic range and an excellent output signal-spur ratio with a high gain,which significantly improves the performance of the MORSE system.