True Time-delay Optical Beamforming Technology With Optic Switched Differential Structure And Its Application In Radar Target Direction Finding

The future communication system requires that the next generation satellite communication must have wide-angle scanning ability.The signal bandwidth of radar determines the range resolution of radar beam to the detected target.Traditional satellite communication and radar detection systems have defects in bandwidth and capacity.The application of optical beamforming technology to satellite communication and radar systems can greatly improve the instantaneous bandwidth and channel capacity of the system,and it also can overcome the aperture effect on radar bandwidth limit.Therefore,the optical control beamforming technology has become the focus of the new generation satellite communication system and radar detection system,and it is also the main research content of this paper.Based on the theoretcal analysis of the photonics-based optically controlled beamforming,this paper focuses on the implementation and application of optically controlled beamforming network.The main work of this paper is organized as follows:1.The influence of the differential true time-delay network amplitude and phase consistency on the antenna system is studied.Through theoretical derivation,the broadband characteristics of the optical delay phase-shift network are proved;through simulation,the influence of phased array antenna system amplitude and phase consistency on beam pointing angle,bandwidth characteristics and sidelobe level of the system is analyzed.Precision fiber optic true time delay lines are especially important for antenna systems.2.A high-precision optic switched differential structure true-time-delay phaseshift beamforming network is developed.Based on the high-precision optic switched delay line measurement and production platform,a 4-channel 5-bit programmable optical beamforming network is developed,and the performance of network is tested experimentally.The experimental results show that the delay accuracy is better than±0.5 ps,which is higher than similar delay lines have been domesticly reported,the insertion loss consistency is better than ±1 d B.In order to verify the delay phase shift function and broadband characteristics of the system,the experiments of both the single tone and broadband signal synthesis and cancellation are carried out.The experimental results of both the single tone and broadband signals show that compared with the single channel signal power,the signal power increment is close to 6 d B,and the signal suppression in cancellation is greater than 20 d B.3.A synthetic beam optical power direction finding scheme based on interferometer direction finding system is proposed and verified.The scheme is based on an optical switch differential true delay network,and the azimuth angle of the transmitting antenna is obtained by measuring the amplitude increment of the composite signal of two receiving antenna units;and an experimental link is built in the dark room to measure the incident angle of the signal entering the radar.Through amplitude calibration and selection of reference angle,the accuracy of angle measurement can be greatly improved.The experimental results show that the direction finding accuracy of 0.2° can be achieved by using either single-tone signal or broadband signal direction finding.Finally,the direction finding error is analyzed,which provides research ideas and directions for improving the system accuracy in the future.