Low Spurious, Broadband Reflection Frequency Modulation Using an Active Metasurface

By employing varactor diodes in a metasurface, the resonance frequency of a high-impedance surface (HIS) can be changed by a bias voltage. To modulate the frequency of the reflected wave from such surfaces, a phase variation of more than 360° is required. To overcome the phase variation limitation (< 360°) in a conventional active metasurface, we fabricated a metasurface with two resonances and manipulated both poles simultaneously to achieve a phase variation exceeding 360° for smooth modulation of the reflection frequency. Because of this wide variation in the reflection phase, it is possible to modulate a broad range of frequencies between 2.75 and 3.25 GHz with up to 1-MHz variation in the modulation frequency. The best spurious-free dynamic range (SFDR) for this frequency range is 20.7 dBc at 3.25 GHz.