This letter presents the design of wideband, low-cost, single layer, ultra-thin, beam scanning circularly polarized reflectarray (CP-RA) antenna with high radiation characteristics. To obtain an efficient single and multiple CP beams, a sub-wavelength unit cells based on Pancharatnam-Berry (PB) geometrical phase was used to increase the beam scanning efficiency. PB unit-cell with periodicity of $0.28\lambda_o$ and ultra-thin thickness of $0.11\lambda_o$ is used to achieve the required phase correction across the reflectarray aperture to produce a collimated RHCP beam in the desired direction. The unit cell has three plasmonic resonances and the proposed CP-RA composed by $43\times 43$ PB unit cells and occupied an area of $215 \times 215 mm^2$ . Both simulation and experimental results show that the proposed CP-RA produces RHCP pencil-beam in the desired direction with a 1-dB gain BW of 24.5% from 17 GHz to 24.5 GHz, 3-dB gain BW of 46.15% from 15 GHz to 24 GHz, peak aperture efficiency of 49.93%, 3-dB axial ratio of 46.15%. Furthermore, a beam scanning with $70^\circ(\pm 35^\circ)$ scanning angle is achieved with gain scan loss of less than 3 dB and beam squint of less than 1.3° within the whole frequency band and for all scanning angles.

The design and implementation of a reflectarray with a single-layer perforated dielectric substrate is presented. The perforated dielectric layer, used as the reflecting surface of the proposed antenna, is realized by drilling air holes with different diameters on the dielectric substrate. Thus, the effective permittivity of the dielectric substrate is altered by drilling holes with different diameters, and then the substrate is equivalent to an inhomogeneous dielectric layer that can be controlled by these holes to collimate the reflected waves in the special direction. The reflectarray is composed of 29 × 29 elements, and it covers an area of 24.65 × 24.65 cm². Varying the hole's diameter can lead to 360 phase shift. The reflectarray is offset fed by a linearly polarized pyramidal horn antenna. Full-wave analysis software CST Microwave Studio, which is based on finite integration technique, is applied. The results are validated by measured results. The 3-dB beamwidth is 2.7°. A peak gain of 35.5 dB is predicted at 30 GHz. The reflectarray can cover Ka-band with sidelobe level below -20 dB for both E-plane and H-plane.

W-band planar perforated dielectric substrate lens antenna is designed and implemented. The lens utilizes a perforated dielectric multilayer substrate that converts spherical wavefront into planar wavefront. The dielectric perforation is performed with air holes, and each hole has a uniform diameter through all layers for simplicity. The transmission coefficient phase is controlled locally. The lens is designed at 94 GHz and composed of 29 × 29 elements that cover an area of 58×58 mm². The lens is center-fed by a WR-10 rectangular waveguide located at 44.5 mm from the lens making an aperture angle of 42 ^°. Two lenses are investigated, a single-layer lens and a six-layers lens. The six-layers lens provides 30 dB gain, which is 1.7 dB higher than the gain provided by the single-layer lens at 94 GHz. The numerical and measured results are found to be in good agreement.

An enhanced reflectarray (RA) antenna built of elements with reduced reflection phase sensitivity is presented. The proposed unit element is composed of a concentric, multi-resonance circular-ring structure with variable sizes. By changing the outer and inner radius of the interior ring in the opposite directions, a reduction in the phase sensitivity without dedicating to the 360° phase range and aggravating the losses in the unit element is achieved. Thus, this has given a good manufacturing tolerance with a high-efficiency wideband performance. Measurement results show the maximum gain of 26.4 dBi at 10 GHz, aperture efficiency of 44.27%, and 16.3% 1dB gain bandwidth. In order to improve the bandwidth of antenna, the phase constant ($\phi_{\circ}$) value at the RA aperture is gradually tuned and optimized. The designed antenna with $\phi_{\circ}$=-125° has a peak gain 26.6 dBi at 10.2 GHz, aperture efficiency of 44.56%, and the 1dB gain bandwidth is about 23.3% (9.67-12 GHz). In comparison with the conventional antenna ($\phi_{\circ}$=0°), the 1 dB bandwidth shows a 43% improvement.

In the past few years, orbital angular momentum (OAM) has aroused great interest in the scientific communities, because it shows great potential for enhancing capacities of radio and optical communication systems. Here, we propose anisotropic metasurfaces to generate multiple OAM vortex beams at microwave frequencies. A phase compensation theory is presented, in order to determine the phase distributions on metasurfaces, This theory enables independent control of beam numbers, polarizations, orientations, and topological charges of OAM vortex beams, respectively. The metasurface is composed of anisotropic elements, whose reflection phases can be engineered separately in different polarization directions. The scheme is validated by both simulation and experimental results and shows great potential for the polarization division multiplexing in OAM communication systems.

A wideband reflective polarization rotator featuring a single layer and vialess design is proposed in this letter. The curved bowtie resonator is employed to accomplish wideband performance. Two notch resonators are etched at both terminals of the bowtie resonator to widen the operating bandwidth. Perforated air holes are utilized to improve the polarization conversion ratio at the high-frequency band. The proposed design exhibits four resonant frequencies at 17.3, 26.4, 44.4, and 56.2 GHz with polarization conversion ratio above 89% from 16.2 to 57 GHz, which represents 111.5% operational bandwidth. The structure thickness is 0.085 λ _max , where λ _max is the free-space wavelength at the lowest operating frequency. The development process of the unit cell is illustrated originating from the simplest resonator shape, strip resonator. To verify the simulated results, a prototype is fabricated and measured. The fabricated prototype consists of 40 × 40 unit cells. A comparison with related recent designs is performed to investigate the notability of the proposed design regarding the wideband performance and required topology.