A Low-Profile Antenna System for Generating Reconfigurable OAM-Carrying Beams

Abstract

A 1 × 4 antenna feeding network is introduced with the capability of generating the required phase distribution for exciting orbital angular momentum (OAM) modes <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 1. The proposed structure includes an equal power divider and four 1-bit phase shifters. Switching the state of phase shifters between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm 45^\circ$</tex-math></inline-formula> , [0, 90, 0, 90] phase distribution is achieved in clockwise and counterclockwise directions. In case a uniform circular array (UCA) with a mirror image configuration is used, the phase distribution of [0, 180, 180, 0] is automatically produced between the antenna elements. Thus, the combination of feeding network and UCA will bring about the desired condition for exciting OAM modes +1 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 1. Furthermore, it is explained that by cascading another phase shifter to each of existing ones, the possibility of generating OAM mode 0 is obtained. A prototype of the suggested structure operating at 2.45 GHz is designed, fabricated, and measured. Upon evaluating the radiation characteristics of the system, reconfigurable beams with helical phase fronts and owing the null in the broadside are observed.