Fine-Time Resolution Passive RF Source Imaging

射频(RF)感知和通信现在无处不在。此外，随着射频发射是使用通用半导体技术产生的，随着可用的频谱变得越来越拥挤，民用和军用系统不可避免地融合在一起。因此，所有系统现在的特点都是频率、波束模式和脉冲模式灵活；因为技术允许这样做。雷达系统将利用敏捷性来避免检测，并在交织多个服务功能时避免干扰或模糊，而通信系统将再次利用敏捷性来搜索与变化的数据速率需求匹配的带宽。因此，通过被动监控射频传输来获得态势感知的问题变得越来越困难。雷达和通信系统不再以稳定的重复信号结构为特征，因此很难从单个来源收集足够的能量来检测它们，更不用说确定它们的特征或定位了。因此，不仅需要利用直接视线信号，而且需要利用主源的多径反射。特别令人感兴趣的是分析与特定源有关的信号中的更详细的细节，以便通过可以被描述为源图像的方式重建对源本身的更详细的理解。反射信号的功率往往低于直接拦截，要达到可接受的性能，很可能需要使用能够共享信息的多个传感器和合成孔径技术来获得分辨率。

Radio Frequency (RF) sensing and communicating is now ubiquitous. Moreover, with RF emissions being generated using generic semiconductor technologies and with the available spectrum becoming ever more crowded, there is an inexorable convergence of civilian and military systems. Thus all systems are now characterised by frequency, beam-pattern and pulse-pattern agility; because the technology allows it. A radar system will exploit agility to avoid detection and to avoid interference or ambiguity while interleaving multiple service functions whereas communication systems again exploit agility in the search for bandwidth matching varying data rate needs. Thus the problem of gaining situation awareness, by passively monitoring RF transmissions, is becoming ever more fraught with difficulty. Radar and communications systems are no longer characterised by steady repetitive signal structures and as a result it is difficult to collect enough energy from individual sources to detect them, let alone to characterise or locate them. Thus there is a need to exploit not just the direct line-of-sight signals but also to multi-path reflections of the primary source. Of particular interest is the analysis of finer details in the signals relating to a specific source in order to reconstruct more detailed understanding of the source itself, via what might be described as a source image. Reflected signals will tend to have lower power than the direct interception and it is likely that acceptable performance will require the use of multiple-sensors able to share information and synthetic aperture techniques to gain resolution.