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 between 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.
Left-handed metamaterial coatings for subwavelength-resolution imaging
