Twisted Beams With Variable OAM Order and Consistent Beam Angle via Single Uniform Circular Arrays

Paolo Burghignoli,Francesco Mancini,Davide Comite,Walter Fuscaldo,Alessandro Galli,Paolo Baccarelli

doi:10.1109/access.2020.3021503

Paolo Burghignoli, Francesco Mancini + Show 4 more

Open Access

https://doi.org/10.1109/access.2020.3021503

Copy DOI

Abstract

A planar antenna radiating twisted beams with different azimuthal order and a consistent beam angle is designed by employing a single uniform circular array embedded in a Fabry-Perot cavity. Circular phased arrays placed in free space are commonly employed to radiate conical beams carrying orbital angular momentum. However, the beam angle depends on both the array radius and the azimuthal order of the beam, thus requiring the use of multiple concentric circular arrays in order to produce beams with different azimuthal order and a common beam angle. In the proposed design, this is simply achieved by exciting higher-order cylindrical leaky waves through a single circular array feeding a Fabry-Perot cavity. Such waves radiate conical patterns whose beam angle is mainly determined by the relevant radial wavenumber and only weakly depends on the azimuthal order. In particular, we propose here an antenna design capable of radiating beams with azimuthal orders 0, ±1, ±2, and ±3 in the microwave range. The cavity is fed by an array of coaxial probes optimized for input matching through the inclusion of parasitic metal pins. Numerical full-wave simulations validate the effectiveness of the proposed design in terms of radiation patterns, passive input scattering parameters, and active input reflection coefficients.

Highlights

Twisted electromagnetic waves have been the subject of intense investigations in the last decades since the seminal paper by Allen et al, where optical beams with helical wavefronts were shown to carry orbital angular momentum (OAM) [1]
In this paper we aim at showing that the same result, i.e., consistent beam angle among different OAM orders, can be achieved by using a single uniform Circular Arrays (CAs) (SUCA), provided that the array is not placed in free space
NUMERICAL RESULTS full-wave results obtained with CST Microwave Studio are reported for both the radiation patterns of the Fabry–Perot cavity antenna (FPCA) and the relevant input parameters at the SUCA ports, in order to validate the effectiveness of the proposed design

Summary

INTRODUCTION

Twisted electromagnetic waves have been the subject of intense investigations in the last decades since the seminal paper by Allen et al, where optical beams with helical wavefronts were shown to carry orbital angular momentum (OAM) [1] Applications of such OAM waves have been investigated in all frequency ranges, from radio frequencies to optics, X- and gamma-rays [2]. In this paper we aim at showing that the same result, i.e., consistent beam angle among different OAM orders, can be achieved by using a single uniform CA (SUCA), provided that the array is not placed in free space (cf Fig.1(a)) but inside a Fabry–Perot cavity (cf Fig.1(b)) Such a cavity supports leaky modes, that may be excited by the SUCA in the form of cylindrical leaky waves (CLWs) propagating radially with a complex wavenumber kρ = β − jα.

OPERATING PRINCIPLE

FEEDER DESIGN

NUMERICAL RESULTS

CONCLUSION