Generating Circularly Polarized Vortex Electromagnetic Waves by the Conical Conformal Patch Antenna

The generation of vortex electromagnetic (EM) waves carrying orbital angular momentum (OAM) has attracted more and more attention due to its special characteristics and potential applications. In this paper, the circularly polarized vortex EM waves with different OAMs have been generated at 2.4 GHz by a novel conical conformal patch antenna (CCPA) consisting of a conical substrate, a correspondingly conformed circular-ring metallic patch, and a single-feed point. First, we analyze the radiated field of a standard circular-ring patch, in which a circularly polarized TM $_{nm}$ mode excited by two coaxial feeds can generate the circularly polarized OAM wave with the topological charge of $l = (n - 1$ ). Then, a pair of the slot is added to the CCPA for obtaining a simpler structure with a single feed point. By adjusting the size of the slot and the angle between the slot and the single-feed point, two orthogonal modes with the same amplitude and a relative 90° phase shift can be obtained for generating the circularly polarized vortex wave. In addition, we have also tried to use an additional conical horn outside of the CCPA for enhancing the performance of the antenna. Finally, in order to validate the theoretical results, we have also fabricated and measured the CCPA, from which we can confirm that our design is efficient for generating the vortex waves.