National Laboratory of Photonic Networks, Inter-university National Consortium for Telecommunications (CNIT), Via Moruzzi 1, 56124 Pisa, Italy.
TeCIP Institute, Scuola Superiore Sant'Anna, Via Moruzzi 1, 56124 Pisa, Italy.
Nature. 2014 Mar 20;507(7492):341-5. doi: 10.1038/nature13078.
The next generation of radar (radio detection and ranging) systems needs to be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. Today's digital microwave components (synthesizers and analogue-to-digital converters) suffer from limited bandwidth with high noise at increasing frequencies, so that fully digital radar systems can work up to only a few gigahertz, and noisy analogue up- and downconversions are necessary for higher frequencies. In contrast, photonics provide high precision and ultrawide bandwidth, allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimetre waves, and the detection of such signals and their precise direct digitization without downconversion. Until now, the photonics-based generation and detection of radio-frequency signals have been studied separately and have not been tested in a radar system. Here we present the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR. The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radio-frequency up- and downconversion and guaranteeing both the software-defined approach and high resolution. Its performance exceeds state-of-the-art electronics at carrier frequencies above two gigahertz, and the detection of non-cooperating aeroplanes confirms the effectiveness and expected precision of the system.
下一代雷达（无线电探测和测距）系统需要基于软件定义的无线电来适应可变的环境，使用更高的载波频率来缩小天线尺寸，并拓宽带宽以提高分辨率。如今的数字微波组件（合成器和模数转换器）在频率增加时，带宽有限且噪声较高，因此全数字雷达系统的工作频率只能达到几千兆赫，而更高的频率则需要噪声较大的模拟上变频和下变频。相比之下，光子学提供了高精度和超宽带宽，允许灵活地生成具有任意波形的极其稳定的毫米波射频信号，并对这些信号进行检测和精确的直接数字化，而无需下变频。到目前为止，基于光子学的射频信号产生和检测已经分别进行了研究，但尚未在雷达系统中进行测试。在这里，我们展示了在 PHODIR 项目中开发和进行的全光子相干雷达演示器的结果。所提出的架构利用单个脉冲激光器来产生可调谐的雷达信号并接收回波，避免了射频上变频和下变频，同时保证了软件定义的方法和高分辨率。其性能在 2 千兆赫以上的载波频率上超过了最先进的电子技术，对非合作飞机的检测证实了该系统的有效性和预期的精度。
