A Novel Wideband Multimode Orbital Angular Momentum Antenna Based on Tightly Coupled Array

In this letter, a wideband multi-mode orbital angular momentum (OAM) array antenna is analyzed and presented. For the multi-mode characteristic, 12 uniform dipole elements are sequentially rotated by 30<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> to form a circular array, generating the 11 OAM modes ranging from -5 to +5. For the wideband characteristic, the elements are tightly coupled and loaded metasurface structures on both overlay and surround surfaces, enabling the active return loss of the antenna of all OAM modes to consistently remain below -10dB across the 5 - 6GHz operational bandwidth. For obtaining the corresponding excitations, a feeding network composed of a 1-to-12 power divider and 30<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>-step 4-bit phase shifters has been designed. Measured results show that the proposed OAM antenna has good wideband and multi-mode characteristics.