Research On Fiber Opticdelay Line And Multi-beam Forming

The traditional phased ar ray radar by means of t he phase shifter has been matured.However the br oadband and wide-a ngle scanni ng of the phase d a rray r adar is r estric ted bec ause of its transition time and a perture. Us ing optical re al-time delay t echniques, the optical phased radar can eliminate the aperture effect and the beam squint problem. The major advantages of optical phased radar include t he smal l size, small weight, low loss,EMI immuni ty, etc. Multi-beam optical phased array achieved by using optical ti me delay line can reduce the searc h interval time. Using the splitting and c ombini ng of s pectr al light, it is easy to i mplement the multi-beam.Firstly, the model of optical phased arra y ra dar for numeri cal simul ation is established in this thesis, and the theoretical formulas of the various performance parameters are de duced. The factors that influence the bandwidth and the beam squint are the oretically analyzed to the structure of optical phased array radar that uses opti cal real-time delay on the sub-ar r ay, and are simulated on the Matlab platfor m.Se condly, t he model of the optical de tecting section is bui lt, and the theoretical formulas of the noise figure are de r ived. In the c ase of ignoring fr equency dependence,the small-signal model of intensity modulated opt ical link for direct defect ion is established, the express ions a bout nois e figure and gain are deduced. Then the model of optical phased a rray is esta blished, and the formula of noise figure is derived by using the expre ssions of gain and noise figure in optical link. The factors that infl uence noise figure are analyz ed such as attenuation fiber-opti c link, t he number of array elements and the preamplifi er gain. For t he presenc e of detect ing saturation, the noise fi gur e of 8-element linear array is 3.83 dB. For the presence of link noise signals, the 16- and 32-element linear array are simulated. The nois e of optical link can cause the rising of the bea m sidelobe level. When the SNR is less than 15 dB, t he sidelobe level will r aise a lot.Then, the sources and the effects of the delay error that caused by temperature,element failure e r ror and random error are introduced. Moreover, the formulas of the s idel obe and the beam squint are theore tic al deduced, the i nfluenc es of random ampl itude and phase errors on beam and simulation are analysis. The mai n affect s of delay error on beam is the beam pointing angle. The relationship formula between the mean squa r e value of del ay error and the beam squint is deduced. In the range of 0~3ps,the graph t hat is drawn using t he mean squa r e value of the 100 points is consistent wit h the graph that is drawn by using t he theoretical formula, where the 100 points are the s imulation results of the beam in the pres ence of the delay error. The sidelobe is mainly affected by the amplitude error, The greater the error i s, the more sidelobe l evel raise.Finally, the basi c principles of a multi-beam formi ng are i ntroduce d, and it s s tructure is designed and each beam c an be i ndependently scanning. The signal frequency is 10 GHz, the amplitude error obeys normal distribut ion with zero mean, and the struc ture of 4 beams and 16 el ements is si mulated. The result s show that when the mean square errors of amplitude error are-5dB and-3dB, the be am squint are 0.3°and0.6°. And when the mean square errors of delay error are 2ps and 3ps, t he sidelobe raise1.97dB and 2.64dB.