【作者】 周鹏；

【导师】 皮亦鸣；

【作者基本信息】 电子科技大学 ， 信号与信息处理， 2008， 博士

【摘要】 双基地SAR具有隐蔽性强、抗干扰、信息获取丰富、可前视成像等诸多优点，是目前雷达技术领域的主要研究热点之一。早期研究以对称体制为主，如：卫星发射／卫星接收、飞机发射／飞机接收等。随着这类系统的不断发展，非对称体制的双基地SAR也逐渐成为一种新的研究方向。本文以低轨道雷达卫星发射、飞机接收的组合——星机双基地SAR为研究对象，在未来雷达卫星星座的支持下，该系统可将星载SAR覆盖面大、安全性好和机载SAR机动灵活、分辨率高的优点结合在一起，具有广阔的应用前景。星机双基地SAR在理论和技术上都面临很多挑战。首先，目前相对更成熟的机载双基地SAR、星载双基地SAR的很多理论无法直接应用，需重新研究；第二，由于雷达卫星的速度远快于飞机，收、发波束足迹的空间同步是关系到星机双基地SAR能否具有实用价值的最核心技术。这里的空间同步涉及两方面：一是如何尽可能地提高场景长度，二是如何实现空间同步误差的补偿；第三，与其它类型的双基地SAR类似，时间、频率、相位同步也是必须解决的关键技术。本文针对上述问题，开展了较为系统的研究，完成的主要工作和贡献如下：1)较全面地研究了星机双基地SAR的系统理论。研究了主要技术指标所能取得的量级、飞机飞行参数的约束条件、工作模式、距离史、多普勒参数、信号模型等内容。2)分析了空间、时间、频率、相位四种同步误差对系统性能指标的影响，明确了各种同步机制的必要性，推导了对“剩余同步误差”的量化指标要求。3)针对已有文献中一种基于“双向滑动聚束式”空间同步方法(DSS方法)所做的几条影响实用性的假设：卫星沿直线匀速飞行、地球表面是一个平面、飞机与卫星平行飞行，对原方案的控制模型进行了改进，使该方法更加实用化。4)针对DSS方法场景长度偏短的缺点，提出了一种基于“卫星宽波束／飞机反向滑动聚束式”的空间同步方法。该方法可在方位分辨率相等的前提下，获得更长的场景长度。5)针对DSS方法所需成像算法复杂的缺点，提出了一种基于“双宽波束式”的空间同步方法。由于收、发双方均无需波束指向控制，成像算法简单。“宽波束接收式”是“双宽波束式”中卫星波束展宽倍数等于1的一种特例，由于无需改动卫星波束，可应用于非合作式系统。6)对已有文献中一种只能用于“双向滑动聚束式”的空间同步误差补偿方法进行了改进，改利用直达波栅瓣为利用主瓣，使之可应用于另外两种模式。7)对已有文献中一些基于直达波的时间、频率同步方法进行了改进，无需借助其它技术手段就能估计出直达波的多普勒质心，从而可直接估计出时间、频率同步误差；对已有文献中一种专为星地双基地SAR设计的时间对齐方法进行了改进，使之可应用于星机双基地SAR。本文针对星机双基地SAR的“系统理论”、“空间同步”、“时间同步”、“频率及相位同步”等关键技术开展了较为深入和系统的研究，取得了一定的成果。下一步，在条件允许的情况下，希望开展一些地面成像实验，为将来实际系统的研制打下更坚实的基础。更多还原

【Abstract】 In recent years bistatic SAR has been gaining more and more interest because ofsuch specific advantages as reduced vulnerability in military system, anti-disturbingcapability, providing additional information about the target and imaging in flightdirection. Most of the previous studies focused on the systems with symmetricalstructure like spaceborne or airborne bistatic SAR. With the development of thesesystems, bistatic systems with asymmetrical structure are emerging as a new researchtopic.This dissertation carries out research on spaceborne/airborne hybrid bistatic SAR(SA-BSAR), which consists of a radar satellite as the illuminator and a receivermounted on an aircraft. Under the support of the future radar satellite constellation,SA-BSAR may combine high invulnerability and wide coverage provided by thespaceborne transmitter with the great maneuverability and the high resolution providedby the airborne receiver. However, SA-BSAR faces a lot of theoretical andtechnological challenges as well as possessing great potential. First, many correlatedbasis theories must be studied since many of the existing theories, developed forspaceborne or airborne bistatic SAR, are unsuitable for SA-BSAR. Second, the biggestchallenge is the space-time synchronization of the antenna footprints due to the extremeplatform velocity differences. There are two aspects involved: (1) how to improve thescene extension as much as possible, (2) how to compensate the spatial synchronizationerror. Third, similar as other types of bistatic systems, time, frequency and phasesynchronization are also the key techniques to be solved.Focusing on the above challenges, systematical studies have been performed andthe main work and the contributions are presented as follows:1) A relatively comprehensive study on the correlated basis theories are carried out.The research subjects include: the quantitative levels of the main technical parameters,the constraints of the aircraft flying parameters, operation modes, range history, Dopplerparameters, signal model, and etc.2) The influences of the synchronization errors on the imaging performance are analyzed. The necessities of the spatial, time, frequency and phase synchronizationmeasures are confirmed. The requirements on the residual errors are derived.3) Based on an existing spatial synchronization approach relying on ’double slidingspotlight mode’ (hereafter referred as DSS approach), a mathematical model for beamsteering is presented and a set of concerned formulae is derived to cancel suchassumptions in DSS approach like fiat-earth geometry, straight-line trajectories, andparallel trajectories between the platforms.4) A new spatial synchronization approach based on ’wide-beam illumination andinverse sliding spotlight receiving mode’ is proposed. This approach provides, with thesame azimuth resolution, a longer scene extension than the length achieved by DSSapproach.5) A new spatial synchronization approach based on ’double wide-beam mode’ isproposed. This approach avoids a complicated imaging algorithm since it does not needbeam steering. ’wide-beam receiving mode’, a special case of’double wide-beam mode’,can be applied to a non-cooperative SA-BSAR because satellite beam pattern has not tobe altered.6) An existing approach dedicatedly designed for ’double sliding spotlight mode’and used to compensate the spatial synchronization error, is modified to adapt for theother two operation modes. Grating lobes of the direct-path signal are substituted withmain lobes in the modified approach.7) Several modified and more practical approaches via direct-path signal for timeand frequency synchronization are proposed. The modified approaches directly estimatethe synchronization errors without the assisted means to estimate Doppler centroid ofdirect-path signal. An existing approach used to temporally align the echo data with theorbit data in space-surface bistatic SAR is modified to be suitable for SA-BSAR.Systematic studies are carried out for several key techniques of SA-BSAR,including: ’system theories’, ’spatial synchronization’, ’time synchronization’, and’frequency and phase synchronization’. In the next step, some imaging experiments onthe ground are expected to be performed.更多还原