Continuous beam steering with a varactor-based reconfigurable intelligent surface in the Ka-band at 31 GHz

Varactor diodes have been proposed as active tuning elements of reconfigurable metasurfaces in the Ka-band. However, their experimental realization in this frequency range has not been demonstrated yet. We report the implementation of such a reconfigurable intelligent surface (RIS) made of 20×20 unit cells. By active tuning of the bias voltage of the varactors, the phase of the backward diffracted wave can be continuously tuned between 0° and 180°. Thus, the phase tuning can be independently controlled for each unit cell. The frequency working range of the RIS is 1.1 GHz (from 30.6 to 31.7 GHz). As an illustration of the practical use, we demonstrate continuous beam steering of microwave radiation at 31 GHz in a defined propagation plane.