A Compact Reconfigurable Orbital Angular Momentum Antenna Based on a Single Spoof Localized Surface Plasmonic Resonator

In this work, we propose a compact reconfigurable antenna that utilizes a single spoof localized surface plasmonic resonator (SLSPR) to generate vortex beam radiation with multiple orders of orbital angular momentum (OAM) modes and facilitate mode switching. Both simulated and measured results of radiation patterns and electric field distributions indicate that seven distinct OAM modes (with mode numbers ranging from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = -3 to +3) can be produced at frequencies of 2.471, 3.745, 4.536, and 5.047 GHz, each exhibiting a mode purity exceeding 94%. By simply loading a metallic disc on the surface of SLSPR, mode switching can be easily realized between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = ±1 and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = ±2 at the same frequency <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 3.787 GHz. In contrast to previous OAM antenna designs using spoof surface plasmons, the proposed OAM antenna offers several benefits, including a compact structure, high mode purity, and reconfigurability. These features make our design highly promising for improving spectral efficiency and expanding channel capacity in wireless communication systems, as well as enabling information encryption in secure communication systems.