## 1 Introduction  
OAM is one of the fundamental physical quantities of electromagnetic waves. OAM can theoretically achieve larger channel capacity and spectral efficiency by using the orthogonality of different OAM modes. Vortex beams have been widely used in super-resolution imaging [1, 2], structure field formation [3, 4], the manipulation of nanoparticles [5], and data communications [6, 7, 8, 9]. Metasurfaces have been reported to generate single-mode vortex beams and multimode vortex beams for generating integer and fractional orbital angular momentum [10], synthesizing arbitrary vortex beams [11], and producing crosstalk-free amplitude-modulated vortex beams [12]. They have also been reported to produce a novel method to control the divergence angle of multimode vortex beams [13], a minimalist single-layer metasurface for arbitrary and full control of vector vortex beams [14], a proposed phase plate for generating superimposed orbital angular momentum states [15], a fully phase-modulated metasurface as an energy-controllable circular polarization router [16], a single non-interleaved metasurface for high capacity [17], a method for independent phase modulation of quadruplex polarization channels enabled by chirality-assisted geometric phase metasurfaces [18], and an arbitrary spin-to-orbital angular momentum conversion of light [19]. Deep recurrent neural networks have also been used to enhance the misalignment estimation of the OAM signal [20]. However, the issues of crosstalk in OAM systemsstill deserve further study. A detailed investigation of the impact of metasurface size on the generation of vortex waves in the near-field has not been conducted. Based on the Pancharatnam-Berry phase concept, an abrupt phase change can be conveniently introduced for fabricating broadband ultrathin metasurfaces [21; 22; 23; 24]. The OAM vortex beams exhibit a helical phase front with an azimuthal phase term of \(e^{\parallel q}\) (where \(l\) represents the mode of vortex beams and \(\varphi\) denotes the azimuthal angle around the propagation axis). Hence, it is a fundamental principle to generate vortex beams with the OAM mode \(l\) by introducing a constant electric current along a circular path with a consecutive phase shift of \(l\varphi\). An analysis of near-field electromagnetic energy densities for uniform circular array-orbital angular momentum has been conducted [25; 26; 27]. The performances of a general formulation employing radiation matrix eigenfields of multi-port antennas to synthesize near-field distributions were investigated. The propagation characteristics of diffraction-resistant Bessel, OAM Bessel, and Airy beams in their actual finite-energy implementation, when they were excited by finite-size antenna arrays, were also investigated [28]. In this article, a near-field calculation model is proposed in Figure 1 to demonstrate ultra-large-scale metasurfaces capable of generating vortex beams. On the one hand, as the metasurface size increases, the resulting vortex waves converge toward the center, creating a stronger doughnut-shaped electric field on the same sampling surface and generating fewer side lobes. On the other hand, with an increase in metasurface size comes stronger anti-interference ability, rendering noise signals ineffective against both the amplitude and phase of the generated vortex waves and the OAM spectrum. A reflection-type metasurface composed of rotated \(EE\) unit cells was further designed and simulated to verify the anti-interference capabilities of a large-scale metasurface. Near-field simulations of the compact metasurface were conducted under both linearly polarized plane waves and circularly polarized plane waves. Additionally, similar near-field simulations were performed for large-scale metasurfaces under identical conditions. Through full-wave simulation, it is feasible to extract the OAM spectrum, amplitude, phase, and purity of the OAM spectrum of the scattered electric field, even in the presence of noise.