Beam Improvement Using Double-Stacked SIW-Typed Metalens and OAM Wavefront Reshaping Method

The EM wave carrying orbital angular momentum (OAM) has a helical phase front and hence called vortex EM wave. This letter presents a theory on the manipulation of vortex waves using metalens with hyperbolic phase compensations. The influence of aperture size on gain and sidelobe levels is studied, and a spectral leakage arising from the truncated Bessel transform is elucidated. Guided by this theory, a cost-effective planar metalens using substrate-integrated waveguides is designed. This metalens consists of two stacked substrates, incorporating 13 by 13 meta-atoms arranged in concentric circular rings. Each meta-atom consists of four layers of double-open square slot patches with varying angles, two substrate-integrated waveguides, and an air gap. The measurement validates the proposed theories. Specifically, the divergence angle of mode -1 is reduced from 43.7° to 9.0° and the gain is increased from 7.55 dBic to 16 dBic. The lens has a bandwidth of 16%.