Badreddine Ratni

Phase-engineered metalenses to generate converging and non-diffractive vortex beam carrying orbital angular momentum in microwave region

In this paper, ultra-thin metalenses are proposed to generate converging and non-diffractive vortex beam carrying orbital angular momentum (OAM) in microwave region. Phase changes are introduced to the transmission cross-polarized wave by tailoring spatial orientation of Pancharatnam-Berry phase unit cell. Based on the superposition of phase profile of spiral phase plate and that of a converging lens or an axicon, vortex beam carrying OAM mode generated by the metalens can also exhibit characteristics of a focusing beam or a Bessel beam. Measured field intensities and phase distributions at microwave frequencies verify the theoretical design procedure. The proposed method provides an efficient approach to control the radius of vortex beam carrying OAM mode in microwave wireless applications for medium-short range distance.

Electronic control of linear-to-circular polarization conversion using a reconfigurable metasurface

A reflective metasurface enabling linear-to-circular polarization (LP-to-CP) conversion is proposed. The metasurface polarizer is composed of active unit cells incorporating voltage-controlled varactor diodes, where the dispersion responses of the cells can be tailored. When illuminated by an incident wave, the metasurface converts the LP wave from the source to a CP one. Moreover, in a single voltage configuration, two circular polarized waves with different handedness can be obtained at distinct frequencies. Such operation can be tuned in frequency by changing the applied voltage along the metasurface. Simulations are performed to verify the concept, and measurements done on a fabricated prototype validate the polarization conversion performances at microwave frequencies.

Design of phase-modulated metasurfaces for beam steering in Fabry-Perot cavity antennas

A simple model allowing us to predict beam steering characteristics in a Fabry–Perot (FP) cavity antenna is presented in this letter. The structure consists of a ground plane and a phase-modulated metasurface used as a partially reflective surface (PRS). The aim of this letter is to present a simple model that allows calculating the necessary phase modulation for a desired beam-steering angle. Furthermore, phase-modulated metasurfaces are designed by varying the PRS inductance, and the model is validated both numerically and experimentally on antennas designed to operate around 2.25 GHz.

Active metasurface for a reconfigurable reflectarray antenna

An active metasurface is used as a reconfigurable reflectarray antenna. The metasurface is composed of unit cells incorporating voltage-controlled varactor diodes, where the dispersion responses of the cells can be tailored. A prototype is fabricated and far-field antenna measurements are performed. We experimentally demonstrate frequency agility over a broad frequency range and beam scanning mechanisms.

Planar metasurface for parabolic reflector antenna: Frequency agility and beam steering

A planar reconfigurable metasurface is used as a parabolic reflector for antenna applications. The metasurface is composed of unit cells incorporating voltage-controlled varactor diodes, where the dispersion responses of the cells can be tailored. The phase characteristics of a parabolic reflector is engineered by judiciously controlling the bias voltage of the varactor diodes on the planar metasurface. The metasurface is illuminated by a microstrip patch antenna. Performed measurements show a directive radiated beam from the antenna system. Frequency agility and beam steering performances are also produced by reconfiguring the metasurface reflector.

Metasurfaces for antennas and sensors

The engineering of metasurfaces for antenna and sensing applications is studied. The metasurfaces composed of LC-resonant cells, are designed to achieve either phase modulation or high quality factor resonances. While the phase modulated metasurface used as a superstrate in a Fabry-Perot cavity antenna, shows the capability to steer the radiated beam to an off-normal radiation, the high quality factor resonant metasurface presents high sensitivity to the presence of substances.