An Ultra-Low Profile Metasurface for Enhanced Non-Diffractive OAM Beam Generation Based on Sparse Feed Array

This paper proposes a novel ultra-low profile transmitted metasurface to generate enhanced non-diffractive orbital angular momentum (OAM) beams, employing a sparse feed array (SFA) to create a quasi-plane wave excitation for the first time. Our simulation indicates that with uniform amplitude excitation, the non-diffraction performance of Bessel beam produced by metasurface, surpasses that of conventional single-feed excitation. Based on this principle, a 5 * 5 sparse feed array is introduced and positioned less than one wavelength from the metasurface, ensuring a quasi-uniform amplitude excitation across all units. Further, this metasurface leverages its flexible phase control capability and integrates the spatial phase, OAM phase, and axicon phase to generate an enhanced high-order Bessel beam. The simulated results confirm a successful non-diffractive Bessel beam generation carrying OAM with mode l = +2, exhibiting reduced beam divergence and higher gain. This design also offers benefits of ultra-low profile, high aperture efficiency, low structural complexity.

A Wideband Multibeam Planar Quasi-Yagi Array Antenna Based on Parasitic Pixel Strips

This letter presents a low-complexity parasitic pixel strip (PPS) structure for array antenna to generate six radiations with flexible beam control. To realize multibeam operation, three groups of symmetrical strip-shaped pixels are integrated with the feed antenna, the connection state of which can be controlled by PIN diode. Leveraging the reconfigurable parasitic configuration, the coupling path of the antenna can be strategically manipulated, achieving the desired multibeam property. Thus, by utilizing the PPS structure in conjunction with a planar quasi-Yagi antenna, this single antenna can operate at four states with beam direction towards 40°, -40°, 0°, along with a dual-beam at +/-45°, within the frequency range from 5.0 to 5.6 GHz. Moreover, a prototype of a 1 * 2 array with the PPS structure is also fabricated to achieve six beams with a scan range of 40°, 20°, 0°, -20°, -40° and a dual-beam at +/-30°. Notably, only four PIN diodes are utilized to implement six radiations, verifying that this approach effectively minimizes the excessive use of switches and extends the variety of beams, which provides a low complexity method for multibeam array antenna without complicated beamforming network. These antennas satisfy the benefits of wideband, planner structure, low structural complexity, low cost, and flexible beam control.