Research On Optical Fiber Synchronous And Switching System For Multichannel Microwave Signals

In the field of radar,semi-physical simulation is an important technique for performance testing,index evaluation and fault diagnosis of modern radar systems under in-field test conditions.In order to study the two-dimensional radar target information of distance and angle,it is of great significance for us to develop a multi-channel wide-band radar semi-physical simulation system.In multi-channel simulation systems,reciprocity between channels requires ps-level accurate synchronization for multi-channel microwave signal exchange,which poses a huge challenge to existing microwave technologies.Therefore,this thesis attempts to overcome the above difficulties by using fiber-optic switching technology.Firstly,the multi-channel microwave signal to be exchanged is modulated onto the optical carrier,and then transmitted and exchanged and synchronized by the optical fiber,and finally the microwave signal is restored by the photoelectric conversion circuit.The main research contents of this thesis are as follows:Firstly,in the electro-optical transmission module,a DC regulated power supply is used to supply power to the entire module,which reduces the interference of the power supply ripple.Based on the negative feedback circuit,the current and temperature control circuit of DFB laser is designed to overcome the influence of temperature on the output optical power of the laser.The output optical power of the laser changes less than 0.1dB within half an hour.Secondly,in the optical switch array module,the 2X2 mechanical optical switch drive circuit is designed.On this basis,the optical switch array is built according to the actual application requirements,and the mutual exchange between the channels is realized in the optical domain.In the process of switching,in order to avoid the occurrence of synchronization across clock cycles,the fiber path length of each channel is compensated.Then,in the photoelectric receiving module,the photodetector restores the microwave signal and the reference signal that complete the channel exchange.After amplification,the amplitude difference and phase difference between the two are detected by the amplitude phase detecting circuit.When the STM32 MCU receives the trigger signal,it begins to perform analog-to-digital conversion on the detection result.The synchronization control program adjusts the compensation amount of the amplitude and phase compensation circuit according to the result of the conversion,so that the plurality of channels reach the amplitude and phase consistency after the switchingFinally,the microwave signal with a center frequency of 800 MHz and a bandwidth of 340 MHz is tested.The results show that the amplitude difference between channels is less than 10%,the phase difference is less than 4°,the clutter suppression ratio of the signal is greater than 65 dBc,and phase noise better than-100dBc/Hz@1KHz.