Frequency-modulated continuous waves driven by a space-time encoding metasurface with nonlinear periodic phases

Pulse compression is an important technology in modern radar systems and drives the developments of modern radar technologies towards higher speed and range accuracy. The frequency modulated continuous wave (FMCW) signals, with the advantages of large time width and large bandwidth, are becoming the typical pulse compression signals.

However, the FMCW signals are mainly generated by Voltage Controlled Oscillators (VCOs) or Direct Digital Synthesis (DDS) technologies, causing high system complexity and integration difficulties with the antenna modules. Therefore, one of the most important questions for researchers is how to develop a low-cost and highly efficient FMCW signal generation method.

In a new article published in Light: Science & Applicationsa team of scientists led by Professors Qiang Cheng and Tie Jun Cui from the State Key Laboratory of Millimeter Waves and Institute of Electromagnetic Space, Southeast University, China, and collaborators have developed a theoretical framework and method for generating and controlling FMCWs spatial propagation behavior simultaneously via a novel STCM with nonlinear periodic phases.

The research team designed a reflection-type STCM with 360-degree full-phase coverage. When biased by the nonlinear periodic voltage control signals, the nonlinear periodic phase responses can be instantaneously obtained and modulated onto the incident electromagnetic (EM) waves. In this way, the FMCW signals can be synthesized with time-varying instantaneous frequencies.

The time-frequency characteristics of FMCW signals based on the STCM are closely related to non-linear periodic voltage control signals. By programming the control signals, different types of FMCW signals can be synthesized on the same STCM if required.

Also, by optimizing the initial stress distributions between different regions of the meta-surface, additional phase gradients can be introduced into the meta-surface and then the directions of propagation of the FMCW beams can be manipulated. The method described will lay the foundation for novel signal pulse compression technologies. The scientists summarize the principle of operation of this work:

“We design a method to generate FMCWs and control their spatial propagation behavior simultaneously for two purposes: (1) to synthesize the FMCW signals by designing the required nonlinear periodic voltage control signals; and (2) to manipulate the propagation directions of the FMCW radiates by optimizing the initial stress distribution between different regions of the metasurface.”

“Compared to the traditional FMCW signal generation method, the proposed method does not require frequency synthesis and phased array antenna modules, which can effectively reduce the cost and complexity,” say the scientists.