Traditional methods of generating vortex beams based on metasurfaces consist mainly in modulating propagation phase or geometric phase. Here, by introducing detour phase, we propose the construction of dual-polarized vortex beam generators in the form of metasurface and metagrating (MG). The phase is modulated through moving the position of meta-atoms instead of varying the geometrical parameters or rotating the unit cells. To use detour phase, two kinds of unit cells are designed to achieve specific diffraction order. Each unit can arbitrarily and independently adjust the operation frequency and diffraction angle of transverse electric (TE) and transverse magnetic (TM) polarizations. Two vortex beam generators are designed and fabricated with different topological charges carried by orthogonal polarizations. To demonstrate the ability to independently manipulate, two polarizations of the generator based on MG are designed in different frequency bands. Both the simulation and experimental results validate the proposed method, showing great potential for polarization division multiplexing in orbital angular momentum (OAM) communication systems.

In this article, a new technique to design a low-profile planar vortex beam generator is proposed based on microwave frequency selective surface (FSS), which is capable of generating orbital angular momentum (OAM) mode under circularly polarized incidence. Such OAM generator is composed of transmissive units distributed over a planar surface. Each unit cell, behaving as a spatial phase shifter, is composed of a stack of patches and grids separated by thin dielectric substrates. In order to reduce the thickness of the device, a rectangular patch is embedded in the middle layer to introduce an additional resonance. Compared to other resonant unit cells, this structure presents nearly perfect efficiency to convert circularly polarized incident wave to its cross-polarized component. A simple equivalent circuit model, composed of transmission lines coupled together with shunt capacitors and inductors, is presented to analyze this structure. The prototype of the proposed planar OAM generator operating in x-band is designed, fabricated, and experimentally characterized. Good agreement is achieved between full-wave simulations and measurements. It is demonstrated that the generator can achieve an efficiency of 85% at 10.7 GHz with an overall thickness of 0.067λ ₀ .

In this paper, a new method for generating high-efficiency vortex beam carrying orbital angular momentum (OAM) mode is proposed based on the miniaturized element frequency selective surfaces (MEFSS) in the microwave region. The unit cell is a class of sub-wavelength periodic structure, which is composed of non-resonant elements with a low profile. A flat metalens is designed to control the wavefront of the propagating electromagnetic waves based on different phase responses of eight kinds of MEFSS unit cells. Under linearly-polarized normal incidence, a vortex beam carrying OAM mode with a topological charge of 1 is excited. The measurement results are in good agreement with the theoretical prediction and full-wave simulation. The proposed method shows great potential applications in generating OAM mode with high efficiency at microwave frequencies.

In this article, two transmissive metasurfaces with different phase control mechanisms and working polarization condition are proposed to efficiently generate zero order Bessel beams (BBs), respectively. For the linear polarization condition, a dual-mode meta-atom constructed by three layers of dielectric substrate and four layers of metal patch is designed. By changing the size of metal patches of meta-atom along x-axis and y-axis, respectively, the phase shift for x- and y-polarized incident wave can be tuned relative independently of 0-2 π while the transmission coefficient keeps high value at 10 GHz. For the circular polarization condition, a sandwich type meta-atom applying geometric phase to realize full phase control while keep high efficiency near 10 GHz is designed. According to the designed phase profile of BBs, select meta-atoms with certain phase and efficiency, then arrange them to construct metasurfaces. Full wave simulation results indicate that the dual-mode metasurface working in linear polarization condition generates BBs with the maximum transmission efficiency 0.79 and 0.85 for x and y polarization wave, respectively, and the geometric phase metasurface working in circular polarization condition generates BBs with the maximum transmission efficiency 0.92. Besides, the propagation characteristics of the excited BBs are studied.

Metasurfaces have attracted extensive attention due to their excellent capabilities in wavefront manipulation. However, chromatic aberration,whichis widely present in phase-modulatedtuning meta-devices, limits their applications in modern communication systems.Far-field achromatismhas been explored but only consideredfor single order diffraction. With increasing demands and studies on multi-beam diffraction, including but not limited to, phase-modulated metasurfaces and metagratings, most of them are not suitable for dispersion manipulation. In this paper, we analyze the achromaticmechanism of diffraction field and propose a feasible solution to coherently control the dispersion on multi-order diffractions simultaneously. Chiral phase is introduced in the meta-atom to engineer the dispersion characteristics. In addition, an achromatic dispersion metasurface is designed for dual-beam generation as proof of concept. The two beams with propagationdirection -35° and +35° show good angle stability at the targeted frequencies of 7 GHz, 10 GHz and 13 GHz. Moreover, the limitations on beamdirection accuracy and metasurface aperture are also discussed. An improvement method that can greatly enhance the accuracy of diffraction angle is further proposed, where the deviation between actual beam angles and expected ones is reduced to below 0.8°,with a 73% enhancement.The proposed work builds up a major advance for diffraction management and shows great potential in wireless communications and radar detection.

In this article, a low-profile planar 1 bit non-diffractive vortex beam generator is proposed based on frequency selective surface (FSS) in microwave region. The characteristic of Bessel beam is introduced to control the divergence of the vortex beam. The proposed unit cell is analyzed through equivalent circuit model. The main resonance is provided by the coupling between the patches and the circular slot grid. A cross patch is embedded in the slot to form another resonance. Two elements with 0° and 180° transmission phase are designed to discretize the phase distribution of the metalens. The simulation results show that the metalens can generate fulfill non-diffracting transmission upon a distance of the 32λ ₀ , verifying the effectiveness of the proposed method.