Electromagnetic vortex carries the orbital angular momentum, one of the most fundamental properties of waves. The order of such vortex can be unbounded in principle, thus facilitating high-capability wave technologies for optical communications, photonic integrated circuits and others. However, it remains a key challenge to generate the high-order vortex beams in a reconfigurable, broadband and cost-effective manner. Here, inspired by the balanced-ternary concept, we demonstrate the reconfigurable generation of order-controllable vortices via cascaded N-layer metasurfaces. We theoretically showed that 3 N − 1 ${3}^{N}-1$ different vortex modes can be generated by cascading N metasurfaces, each one serving as an individual vortex beam generator for the order of 3 k ${3}^{k}$ (k = 0,1,2 …, N − 1 $N-1$ ). As a proof-of-concept demonstration, a reconfigurable generation of 26 different vortex beams, with orders from 1 to 13 and from −1 to −13, is showcased in a broad millimeter-wave region by a cascade of 3 metasurfaces. Our method can be easily extended to vortex beam generator of arbitrary orders in a reconfigurable and easily implementable manner, paving a new avenue towards tremendous practical applications.

Non‐diffraction electromagnetic beams such as Airy beams attract wide exploration in various disciplines owing to its fascinating features and great potential of applications. Although generation and applications of Airy beams are actively studied in the optical regime, applications of Airy beams in the THz or sub‐THz domain are rarely explored. This work proposes a new microscopic technique leveraging a sub‐THz broadband non‐diffraction Airy beam as the illumination beam to improve the image quality, which is named as enhanced sub‐THz microscopy (ESTM). The effectiveness of the ESTM is validated by a metallic sample, which shows that applying broadband measured information can render a better image quality than only using single‐frequency information. By blocking the sample using a scattering obstacle, it is demonstrated that the self‐reconstruction property of the Airy beam can efficiently suppress the distortion induced by the obstacle and good images can still be obtained. In addition, it is shown that the image quality applying a broadband Airy beam is superior to that of non‐diffraction quasi‐Bessel beams and other conventionally used illumination beams for microscopic technique.

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Abstract-A tri-band slotted F-shaped antenna with dualpolarization characteristics for wireless applications is presented. The crooked gap and F-shaped monopole are optimized to achieve triband operation of 2.4, 3.5 and 5.8 GHz with −10 dB impedance bandwidths of 20%, 14.1%, and 13.6%, respectively. Furthermore, by properly inserting an F-shaped strip on the wide-slot ground, the circular polarization (CP) with a 19% (3.3-4 GHz) 3 dB axial ratio bandwidth is obtained. The proposed antenna has a compact dimension of 42×40×1.6 mm 3 . A prototype of the antenna is fabricated and tested, and an agreement with simulated results is obtained.

Complex amplitude modulation metasurfaces (CAMM) that can independently control both amplitude and phase have fostered a broad research interest worldwide due to its more robust wave manipulation capability than metasurfaces that can only adjust phase. Although many CAMM structures have been reported, they still suffer from limitations such as low transmittance, complicated structure, polarization dependence, high cost, and difficulty in fabrication. This work proposes a high-transmission polarization-independent CAMM operating in an ultra-wide millimeter-wave frequency range from 30 to 50 GHz realized by cost-effective and easily implementable manners. Three CAMMs are designed to generate complicated millimeter-wave beams like holographic imaging beam, Airy beam, and vortex knot beam. The presented simulation and experimental results clearly demonstrate the effectiveness of the CAMMs. This work presents a new paradigm for CAMM that can be readily extended to other frequency bands. It may also advance further applications of millimeter-wave beams in communication, imaging and detection.