Research On Integrated Optical TTD Network For Phased Array Radar

Due to the limitation of aperture fill time,traditional phased array antenna can only work in a relatively narrow bandwidth.In recent years,optical true time delay(OTTD)has been proved that it can eliminate the influence of beam squint,and has the characteristics of light weight,strong anti-electromagnetic interference capability,high delay accuracy and so on,hence OTTD attracts widespread attention.With the development of integrated photonics,the realization of on-chip op-tical true time delay network(OTTDN)becomes possible,therefore,optically controlled phased array system based on OTTDN has gradually become research hotpot.In this paper,the key tech-nology of integrated OTTDN that can be used for two-dimensional(2D)phased array antenna is systematically studied.The in-depth analysis about OTTDN is carried out from the following as-pects:the architecture design,the theoretical analysis of integrated optical true time delay line(OTTDL),the implementation and evaluation of performance,as well as the application in phased array radar for beamforming and 2D beam scanning.Firstly,the characteristic parameters of phased array radar are analyzed and then the advan-tages of OTTD in phased array radar are demonstrated.On these bases,an OTTDN suitable for large-scale 2D phased array radar is proposed.This network uses the overall delay of rows and columns,which can greatly reduce the design complexity of OTTDN.Secondly,the binary tunable delay chip based on optical switch is designed and manufactured on silicon-on-insulator(SOI).The single delay chip contains four OTTDLs with different delay steps.The maximum delay value in OTTDLs is 677 ps,which can be used in 8 × 8 phased array antenna for 2D scanning.In the OTTDL,the variable optical attenuator used to improve the link isolation and the photodetector used for real-time monitoring are distributed at intervals.This distribution structure reduces the number of auxiliary components that need to be integrated in the high-precision OTTDL.The foot-print of chip is only 5.7 × 15.8 mm2,and the power consumption of whole chip is 4.32 W.Finally,in order to apply the OTTDN to phased array radar,the delay chip is packaged,the control circuit and control software of the OTTDN are designed,which can realize the efficient control for OTTDL and automatic adjustment for different delay states.To verify whether the OTTDN can work,the performance of OTTDL,OTTDN and control module are measured in experiment.The experimental results show that the delay accuracy of the four OTTDLs are less than 1 ps.The simulation analysis based on these results shows that the maximum beam pointing angle error controlled by OTTDN is less than 0.5°.In the anechoic chamber,the 8 × 8 phased array antenna based on OTTDN successfully realizes the 2D beam scanning,the scanning range is 45°?135°,and the step is 5°.In 2 GHz?4 GHz,the maximum beam pointing angle error is less than 4°,which also includes the pattern error of the antenna unit and the fiber length cutting error,The research results prove that the designed OTTDN can realize the phased array radar with high pointing accuracy and wideband scanning,which provides the technical basis for the development of integrated optically controlled phased array radar.