Shah Nawaz Burokur

Restoring in-phase emissions from non-planar radiating elements using a transformation optics based lens

The broadband directive in-phase emission from an array of sources conformed cylindrically is numerically and experimentally reported. Such manipulation is achieved through the use of a lens designed by transformation optics concept. The all-dielectric lens prototype is realized through three-dimensional (3D) polyjet printing and presents a graded refractive index. A microstrip antenna array fabricated using standard lithography techniques and conformed on a cylindrical surface is used as TE-polarized wave launcher for the lens. To experimentally demonstrate the broadband focusing properties and in-phase directive emissions, both the far-field radiation patterns and the near-field distributions have been measured. Experimental measurements agreeing qualitatively with numerical simulations validate the proposed lens and open the way to inexpensive all-dielectric microwave lenses for beam forming and collimation.

3D printed broadband transformation optics based all-dielectric microwave lenses

Quasi-conformal transformation optics is applied to design electromagnetic devices for focusing and collimating applications at microwave frequencies. Two devices are studied and conceived by solving Laplaces equation that describes the deformation of a medium in a space transformation. As validation examples, material parameters of two different lenses are derived from the analytical solutions of Laplaces equation. The first lens is applied to produce an overall directive in-phase emission from an array of sources conformed on a cylindrical structure. The second lens allows deflecting a directive beam to an off-normal direction. Full-wave simulations are performed to verify the functionality of the calculated lenses. Prototypes presenting a graded refractive index are fabricated through three-dimensional polyjet printing using solely dielectric materials. Experimental measurements carried out show very good agreement with numerical simulations, thereby validating the proposed lenses. Such easily realizable designs open the way to low-cost all-dielectric microwave lenses for beam forming and collimation.

Experimental validation of a transformation optics based lens for beam steering

A transformation optics based lens for beam control is experimentally realized and measured at microwave frequencies. Laplaces equation is adopted to construct the mapping between the virtual and physical spaces. The metamaterial-based lens prototype is designed using electric LC resonators. A planar microstrip antenna source is used as transverse electric polarized wave launcher for the lens. Both the far field radiation patterns and the near-field distributions have been measured to experimentally demonstrate the beam steering properties. Measurements agree quantitatively and qualitatively with numerical simulations, and a non-narrow frequency bandwidth operation is observed.

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.

Sharp fano resonances in Bi-layered symmetric Z-structures

We introduce a novel class of dark modes for electromagnetically induced transparency. These dark modes depend on both near-field and far-field coupling between resonators. As an example, a planar metasurface composed of a bilayer of metallic Z-shaped meta-atoms is investigated. Performed simulations and measurements show the appearance of sharp Fano resonances.

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.

3D field-shaping lens using all-dielectric gradient refractive index materials

A novel three-dimensional (3D) optical lens structure for electromagnetic field shaping based on spatial light transformation method is proposed at microwave frequencies. The lens is capable of transforming cylindrical wavefronts into planar ones, and generating a directive emission. Such manipulation is simulated and analysed by solving Laplace’s equation, and the deformation of the medium during the transformation is theoretically described in detail. The two-dimensional (2D) design method producing quasi-isotropic parameters is further extended to a potential 3D realization with all-dielectric gradient refractive index metamaterials. Numerical full-wave simulations are performed on both 2D and 3D models to verify the functionality and broadband characteristics of the calculated lens. Far-field radiation patterns and near-field distributions demonstrate a highly radiated directive beam when the lens is applied to a conical horn antenna.

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.

All-dielectric microwave devices for controlling the path of electromagnetic waves

All-dielectric devices are designed using Quasi-Conformal Transformation Optics (QCTO) concept and fabricated by additive manufacturing for the control of wave propagation. Three lenses are studied; the first one is used to compensate for the curvature of a non-planar antenna array, the second one to steer an electromagnetic beam and the last one to concentrate an electromagnetic field.