Chirp Sequence-Based Beamwidth Control in a Reconfigurable Intelligent Surface

Reconfigurable intelligent surfaces (RIS) have been attracting attention as a technology to expand coverage, particularly in millimeter-wave communication systems, which are highly susceptible to blockages. RIS can reflect radio waves in arbitrary directions by controlling the reflecting elements, which are numerous to enhance gain. However, while an increase in the number of elements leads to higher gain, it also results in a narrower beamwidth, thereby reducing the effectiveness of coverage expansion. In this study, we aim to extend coverage by expanding the beamwidth through the multiplication of chirp sequences with the reflection phase of each element. This method allows for rapid beamwidth expansion, as the computation is performed solely through matrix multiplication, offering a faster solution compared to conventional methods. The expansion of the beamwidth was confirmed through simulations and experiments using a 28 GHz, 400 -element RIS.