Nanosecond-level time-domain coding metasurface for radar signal generation.

The time-domain coding metasurface (TDCM) offers a rapid and efficient approach for manipulating frequency spectra of electromagnetic waves. To date, not only finite-order harmonics can be generated and coded discretely, frequency modulation of continuous waves has also been investigated. However, limited phase-tuning speed still constrains the modulation bandwidth and practical applications. Here, we report a TDCM capable of nanosecond-level phase tuning as fast as 20 ns within a full 360° tuning cycle. Unlike conventional varactor-based approaches, the proposed TDCM adopts a reconfigurable PIN-diode array, reducing transition time between adjacent states to only several nanoseconds. Furthermore, this approach can be extended to Ku- and even millimeter-wave bands, overcoming the frequency constraint of varactors. To validate its effectiveness, we built a C-band frequency-modulated continuous-wave radar prototype with the metasurface as the signal generator. A high-quality 10-MHz-bandwidth FMCW signal was generated, enabling accurate measurement of a flying drone's range and speed.