###### Abstract  
In this paper, a novel method for generating a circularly polarized (CP) quasi-non-diffractive vortex wave carrying orbital angular momentum (OAM), based on the microwave holographic metasurface integrated with a monopole, is proposed. This method is the combination of the non-diffraction theory and the principle of waveguide-fed-based holography and is equivalent to a superposition of two scalar impedance modulation surfaces. To verify the proposed method, a holographic metasurface generating a left-handed circularly polarized (LHCP) quasi-non-diffractive vortex wave carrying \(-1\) mode OAM at the normal direction, was simulated and analyzed. The metasurface consisted of inhomogeneous slot units on a grounded substrate and a monopole excitation. Moreover, the location distribution of slots was determined by a computed interferogram when the reference wave and the object wave with the non-diffractive feature. Compared with an ordinary vortex wave, the quasi-non-diffractive wave obtained by our proposed method possessed a smaller divergence radius and a stronger electric field strength in the 9 times wavelength range. It paved a new path for manipulating the non-diffractive vortex wave in medium distance without using an external feeding source, which holds great potential for the miniaturization devices applied in medium-distance high-capacity secure communication, high-resolution imaging and intelligent detection. circular polarization; quasi-non-diffraction; vortex; microwave holography; metasurface +
Footnote †: journal: Applied  
transmission and the spiral wavefront, a quasi-non-diffractive vortex wave which possesses almost constant energy can be achieved, which has great potential in the applications of short- to medium-range high-capacity communications, as well as vortex-wave-based high-resolution imaging and detection. Since the vortex wave carrying orbital angular momentum [1] was first provided and defined by [PERSON] in 1992, various approaches of generating and steering vortex waves were widely studied, including the spiral phase plates (SPPs) [2], patch arrays [3], lens [4], computer-generated holograms [5], graphene devices [6], components with vanadium dioxide [7] and reflect/transmit metasurfaces [8; 9; 10; 11; 12]. Due to the advantages of the accurate and flexible manipulation of electromagnetic waves, the metasurfaces [13], as the 2D equivalent ultra-thin metamaterials, have gradually become one of the most effective means for controlling electromagnetic waves. Recently, [PERSON] et al. proposed an envelope-modulation theory-based scheme as a novel route to engineer shaped-tailored metasurfaces [14] for manipulating the orbital angular momentum spectrum in a wide microwave bandwidth, further promoting the broadband of OAM-based applications. They also proposed an ultrawideband single-layer metasurface to generate integer and fractional orbital angular momentum, the generated vortex waves covering the 105% relative bandwidth [15]. [PERSON] et al. proposed a low-profile transmitting metasurface using the dimension extension approach to achieve linearly polarized vortex waves in Ku-band [16], which facilitated the vortex wave-based communication applications. Although these OAM modulators exhibited powerful control on the amplitude, phase and polarization of the spiral waves, the problems of the beam divergence were not considered and well addressed. The diameter of a vortex wave increases gradually as the propagation distance becomes longer, which may have caused the misidentification of the topological modes for the receiving end with a small aperture. To resolve the problem of divergence, the quasi-non-diffractive feature was introduced to the design methods of vortex waves for improving convergence and energy efficiency. [PERSON] et al.