【作者】 房鹏；

【导师】 郑小平；

【作者基本信息】 清华大学 ， 电子科学与技术， 2009， 硕士

【摘要】 电子对抗与雷达是一对矛与盾。雷达除对目标进行监控或跟踪,还要保护自己免受敌方的侦测或攻击,这使现代雷达变得愈加复杂,而相应的欺骗性干扰系统也越来越复杂。光真延时因其大信号带宽、抗电子干扰、传输损耗小、重量轻等优点,在电子对抗中有着明显的优势,而受到广泛的关注与深入的研究。论文面向电子欺骗的要求,对光子技术模拟移动目标的回波进行了探索性研究,取得如下的成果:1、理论上对射频载波的处理过程进行数学描述,并对真延时实现射频信号的多普勒频移进行定量分析和原理验证,揭示了真延时参数与射频信号的多普勒频移之间的定量关系,得出对射频信号进行时变真延时可以实现多普勒频移的结论,从而为利用光真延时模拟移动目标的回波提供了理论依据。2、提出了一种高精度、大延时量的光真延时方案。该方案为级联的两个部分,中间用基于四波混频的全光波长变换器连接:第一级是光开关选择光程的数字式步进延时,用来实现大延时;第二级是基于色散元件的延时,通过调节光波长变换器的泵浦波长来实现延时的准连续调节。3、论文利用高非线性光纤中的四波混频效应实现了全光波长变换。实验研究了在信号光存在副载波调制情况下各种因素对基于高非线性光纤四波混频效应波长变换的影响,为优化波长变换器进而提高光真延时线的传输性能提供了依据。实验结果表明,光波长变换对副载波的主要影响是:副载波线宽略有增加,从63.9599kHz增加到64.2490kHz;带内噪声功率密度变大,在距载波100kHz和500kHz处分别增加了5dB和20dB。4、对使用波长变换器的级联光真延时方案进行了研究。在使用15km单模光纤和色散量为51.1ps/nm的啁啾光纤光栅的级联延时实验中,单模光纤表现出的色散量为10.9ps/nm,小于不用波长变换器时的色散量(典型值255ps/nm)的1/20;实验光链路在1548nm处的总延时达到62.601209μs,且可通过调节光波长使链路的延时从0~509ps准连续可调。更多还原

【Abstract】 In electronic warfare, electronic countermeasures to radar are like spears to shields. Radar has to be able not only to perform the functions of surveillance and tracking, but also to protect itself from potential hostile detection or attack, which makes modern radar become very complicated, and so does the corresponding deceptive jamming system. Superior to traditional electronic countermeasures, optical true-time delay (OTTD) has the advantages of extremely large signal bandwidth, immunity to electromagnetic interference, low transmission loss and light weight. So far, OTTD has attracted much attention and been extensively studied. According to the requirements of electronic deception, this thesis makes an exploratory study on simulating the echo of a moving target by means of photonic technologies. The outline of the thesis is as follows:1) In theory, the radio-frequency signal processing using true-time delay is described mathematically and derived. The result shows the quantitative relations between the true-time delay and the Doppler shift when using time-variant true time-delay to realize the Doppler shift of a radio-frequency carrier. The conclusion is also verified by the matlab simulation. So, it’s feasible in principle to realize Doppler frequency shift using time-variant true-time delay, and the results provide theoretical basis to simulate the echo of a moving target by means of optical true-time delay.2) An optical true-time delay scheme with high precision and a large range is proposed. In the scheme, the time delay is divided into two parts, in between with an optical wavelength convertor (OWC) using partially degenerate four-wave mixing in a highly nonlinear fiber. The first part is digitally incremental time-delay using optical switches and different lengths of single mode fibers (SMFs) to achieve a large time-delay range. The second part is sub-continuous time-delay using a chirped fiber grating (CFG) and tuned by changing the pump wavelength of the OWC.3) All-optical wavelength conversion using partially degenerate four-wave mixing in a highly nonlinear fiber is realized. To optimize the OWC and thus to enhance the performance of the optical transmission link, the impacts of several parameters (such as the pump wavelength and the optical power) on OWC were experimentally studied when the signal light was modulated by radio-frequency sub-carrier. The experimental results showed that due to optical wavelength conversion, the line-width of the radio-frequency sub-carrier increased from 63.9599kHz to 64.2490kHz, and the power density of the in-band noise became larger, e.g. at frequencies 100kHz and 500kHz away from the carrier frequency, the increments of 5dB and 20dB were observed respectively.4) The cascaded optical true time-delay scheme using an OWC is studied. In the experiment using a 15km-long SMF and a CFG with a dispersion of 51.1ps/nm, the SMF exhibited a dispersion of 10.9ps/nm, less than 1/20 of the dispersion of the SMF (the typical value is 255ps/nm) without an OWC. A total delay of 62.601209μs at the wavelength of 1548nm was achieved, and by tuning the pump wavelength of the OWC, a sub-continuous time delay within 509ps was realized.更多还原