Research On Beampointing Control Technology Based On Optical Delay Line Array In Phased Array Radar System

Phased array radar system,as the name implies,is a radar scanning system that uses phased array antenna(PAA)for transmitting(receiving)antennas.The difference with the traditional mechanical scanning radar is that the phased array radar realizes the beam scanning in the far field of the antenna by controlling the phase difference between adjacent array elements of the array antenna.The most important part of phased array radar is the phase shift array unit.The traditional electrical signal phase shifting method based on the electrical delay line and phase shifter array is limited by the delay line length and aperture effect,and the effects of electromagnetic interference.It cannot work under a large instantaneous signal bandwidth.In order to overcome the beam deflection problem of the traditional PAA scanning.We consider modulating the electrical signal on the optical carrier,and controlling the signal delay by optical means.It can overcome the beam deflection caused by the electric phase shifter,resist electromagnetic interference and reduce the weight and volume of the delay line.This paper first reviews the generation and development of phased array radar.Then the principle and advantages of the optical-controlled phased array radar are expounded.Then the research status of the optically controlled phased array radar at home and abroad and the existing problems of the optical true time delay(OTTD)structure are analyzed.The basic principle of the PAA and the pattern of the line array are studied in depth.Based on the basic model and theory of the characteristics of the optically controlled phased array antenna,optimized optically controlled phased array delay array schemes are proposed:(1)Based on the research of traditional OTTD scheme,an OTTD scheme which can generate equal step scanning in the far field of the PAA has been proposed.By controlling the spacing of the Uniform Fiber Bragg Grating(UFBG)array,thereby,the lightwaves emitted from the TLS can be reflected from the corresponding position of the UFBG series.Therefore,a corresponding position difference can be generated at the same reflection wavelength in the adjacent UFBG series,and a corresponding time delay difference can be generated.Thus,an equal step scanning angle can be generated in the far field of the antenna.Moreover,applying the OTTD scheme to a two-dimensional(2-D)plane can also achieve an equal step scan of the antenna far field in two directions of horizontal angle and elevation angle.(2)Based on the one-dimensional and 2-D scanning OTTD system,an optically controlled beamforming network(OCBN)system based on two-dimensional transceiving structure is designed.The system has two modes of operation:the first is 2-D beam scanning,which realizes azimuth and elevation beam scanning;the second type is 2-D reception,which receives signals from different angles of space and performs matched filtering.Achieving 2-D scanning transmit and receive functions through integrated multiplexing of optical devices.(3)Based on above UFBG-based OTTD scheme,the structure of the second-order improve the scanning precision is realized by cascading a wavelength converter(WC)array.Cascading the first-order UFBG array and the second-order high-dispersion fiber(HDF)array through the WC array,so that the wavelength of the light wave emitted by the TLS is adjusted after passing through the first-order delay structure.The second-order time delay is also flexible and adjustable,which can achieve high-precision quasi-continuous scanning of the far field of the antenna.In addition,the first-order delay structure halved the number of fiber gratings due to the introduction of the optical switch,and the wavelength tuning range of the transmitted light wave of TLS is also halved.