摘要
利用光延时技术抑制宽带相控阵雷达的波束色散,光延时量的离散特性会引入波束指向偏差。通过线性相位拟合法分析了最小延时改变对阵面等效相位分布的影响,建立了延时线步进与雷达波束指向偏差间关系的理论模型,得到波束指向偏差与延时步进成正比,与阵元间距、阵元数平方和波束指向的余弦值成反比。通过仿真和实测数据验证了该技术的可行性。实测结果表明,在8~12 GHz宽带微波信号下,±60°扫描范围内,宽带波束的指向偏差小于0.77°,带内指向色散小于0.98°,峰值能量损失小于0.89 dB,旁瓣抑制比超过11.06 dB。
To realize the electrical beam scanning of the phased-array radar,it is necessary to implement true-time delay compensation for the transmitted and received signals in each transmission channel according to the beam direction.Utilizing microwave photonic technology,the microwave signal can be modulated to the optical carrier for transmission and processing.Compared to the frequency of the laser carrier,the relative bandwidth of the microwave signal is extremely narrow.The true-time delay lines based on optical fibers or on-chip waveguides have a large microwave bandwidth,small in-band amplitude and phase fluctuations,and small propagating loss and are immune to electromagnetic interference.The increment of optical lengths of different delay states can be precisely controlled to be far less than a full microwave wavelength.Thus,broadband beamforming can be realized using only subwavelength stepped optical delay lines,which can greatly reduce the beam directional dispersion of broadband microwave signals.The discrete delay values of stepped delay lines lead to discrete directional directions of antenna beams,which results in a certain deviation between the actual and designed directions of the beam.The influence of the minimum delay change on the equivalent phase distribution of the microwave front is analyzed,and a theoretical model of the relationship between delay steps and directional deviations of radar beams is established.The theoretical analysis of beam scanning based on subwavelength stepped optical delay lines shows that the beam directional deviation is proportional to the minimum delay step and inversely proportional to the array element spacing,the square of the number of elements,and the cosine of the beam direction.Through numerical simulation for the X-band wideband radar,the beam direction at each frequency point is almost the same in the frequency range of 8~12 GHz,which indicates that the directional dispersion has been effectively suppressed.It can be observed that some singularities will appear at specific azimuths and delay steps,where the directional deviation will reach extreme values due to the discrete increment of delay.The azimuthal deviation of the singularity gradually increases as the azimuth and the delay step increase.When the delay step is not larger than 3 ps,the azimuthal deviation does not exceed±0.13°,which is less than±1/35 of the narrowest beam width and thus can be almost neglected.Peakpower loss and sidelobe suppression are also simulated.When the delay step is less than 3 ps,the beam peak power drops no more than 0.051 dB,and the in-band fluctuation is less than 0.028 dB.The maximum broadband relative sidelobe power is less than-12.5 dB,and the maximum fluctuation is less than 0.24 dB.Based on the scheme of a subwavelength stepped optical delay line without an electrical phase shifter,9-bit optical delay lines with a minimum delay step of 3 ps are prepared,and the maximum delay exceeds 1.53 ns.The optical delay lines are manufactured by cascaded 2×2 magneto-optical switches and optical fibers.The distributions of the spatial electric field are measured on the nearfield platform and converted to farfield patterns by spherical wave compensation at different designed azimuths and frequencies.When the designed beams point at 0°,30°and 60°,the measured maximum directional deviations are 0.24°,0.28°and 0.77°,and the in-band directional dispersions are 0.21°,0.28°and 0.98°,respectively.Compared to the beam squint based on the scheme of the wavelength stepped optical delay line and electrical phase shifter,the beam directional dispersion is effectively suppressed.Furthermore,under the microwave frequency range of 8~12 GHz and the azimuthal scanning range of±60°,the experimental results demonstrate that the peak power loss can be reduced to less than 0.89 dB and that the sidelobe suppression ratio can exceed 11.06.
作者
刘昂
邵光灏
翟计全
叶星炜
张国强
LIU Ang;SHAO Guanghao;ZHAI Jiquan;YE Xingwei;ZHANG Guoqiang(Nanjing Research Institute of Electronics Technology,Nanjing 210039,China;Key Laboratory of IntelliSence Technology,CETC,Nanjing 210039,China)
出处
《光子学报》
EI
CAS
CSCD
北大核心
2022年第3期174-184,共11页
Acta Photonica Sinica
基金
江苏省高层次创新创业人才引进计划。
关键词
微波光子学
亚波长步进光延时线
光波束形成
相控阵天线
无波束倾斜
Microwave photonics
Sub-wavelength stepped optical delay line
Optical beamforming
Phased-array antenna
Beam squint free
