S. N. Burokur

Tunable bilayered metasurface for frequency reconfigurable directive emissions

The directive emission from a bilayered metamaterial surface is numerically and experimentally reported. The LC-resonant metasurface is composed of both a capacitive and an inductive grid constituted by copper strips printed on both sides of a dielectric board. By the incorporation of varactor diodes in the capacitive grid, resonance frequency and phase characteristics of the metamaterial can be tuned. The tunable phase metasurface is used as a partially reflecting surface in a Fabry–Perot resonance cavity. Far field radiation patterns obtained by direct measurements show the reconfigurability of emission frequency while maintaining an enhanced directivity.

High Beam Steering in Fabry–Pérot Leaky-Wave Antennas

A high-gain low-profile Fabry-Perot (FP) leaky-wave antenna (LWA) presenting one-dimensional high beam steering properties is proposed in this letter. The structure consists of a ground plane and a varying inductive partially reflective surface (PRS). A microstrip patch antenna is embedded into the cavity to act as the primary feed. As design examples, antennas are designed to operate at 9.5 GHz. Subwavelength FP cavities with fixed overall thickness of λ0 /6 (where λ0 is the free-space operating wavelength) are fabricated and measured. The impact of varying the PRS inductance is analyzed. It is shown that a high beam steering angle from broadside toward endfire direction close to 60 can be obtained when judiciously designing the inductive grid of the PRS.

Compact Metamaterial-Based Substrate-Integrated Luneburg Lens Antenna

A compact and small electric-size aperture directive broadband Luneburg lens antenna is presented. The substrate-integrated lens antenna is based on embedding a Vivaldi antenna source inside a parallel-plate waveguide to illuminate a Luneburg lens operating in X-band. The focusing condition of the lens, requiring a gradient refractive index, is achieved through the use of complementary nonresonant metamaterial structures. Numerical simulations are performed to determine the suitable unit cells geometry with respect to the wave launcher inserted into the parallel-plate waveguide. A prototype fabricated using standard printed circuit board techniques has been measured in an anechoic chamber. The electric field distribution inside the antenna system has also been explored using a two-dimensional near-field microwave scanning setup. A good qualitative agreement is observed between simulations and experiments. It has been shown from both far- and near-field measurements that the proposed planar antenna presents good focusing properties.

Low-Profile Substrate-Integrated Lens Antenna Using Metamaterials

A low-profile substrate-integrated lens antenna is designed using planar metamaterials for a broadband operation. The lens antenna is based on embedding a Vivaldi antenna source inside a parallel-plate waveguide to illuminate a half Maxwell fish-eye (HMFE) lens operating in X-band. The focusing condition of the lens, requiring a gradient refractive index is achieved through the use of complementary nonresonant metamaterial structures. Numerical simulations are performed to determine the suitable unit cells geometry with respect to the wave launcher inserted into the parallel-plate waveguide. The electric field distribution inside the antenna system has also been explored numerically. Far-field radiation patterns have been measured on a fabricated prototype in an anechoic chamber. It has been shown from both near- and far-field plots that the proposed planar antenna presents good focusing properties.

Steerable ultra-thin directive antenna from a metamaterial-based subwavelength cavity

We report the design of a steerable directive antenna using a resonant metamaterial-based subwavelength cavity. The cavity is made of a conventional ground plane and a composite metamaterial acting us a partially reflective surface. The antenna is a rectangular microstrip patch designed to operate near 10 GHz. The composite metamaterial is made of a variable capacitive grid and a constant inductive grid. Simulation and measurements show a deflection of the antenna beam of about plusmn20deg for a cavity of thickness about lambda/30.

Direct dark modes excitation in bi-layered enantiomeric atoms-based metasurface through symmetry matching.

We provide evidence for the mechanism of direct dark mode excitation in a metasurface composed of bi-layered Z-shaped enantiomeric meta-atoms. The electromagnetic behavior of the structure is investigated through both numerical simulations and experimental measurements in the microwave domain. We demonstrate direct field coupling excitation of second higher order electric mode under normal incidence based only on symmetry matching conditions. The proposed approach provides a better flexibility in engineering dark mode resonances that do not rely on hybridization mechanism and presents important advantages for multi-spectral sensor applications.

Passive and active reconfigurable resonant metamaterial cavity for beam deflection

The modeling and characterization of an optimized resonant cavity for a passive reconfigurable directive beam antenna near 10 GHz has been presented. It is based on a variable phase metamaterial made of an inductive and a capacitive grid where there is a regular increase of the gap spacing. This variable phase metamaterial allows us to have a forward and backward deflection of up to 30deg. An electronically tunable phase PRS has also been proposed where varicap diodes are implemented in order to achieve shifts in the reflection coefficient phase response. This active PRS has been also employed in a resonant cavity where a shift in the resonance frequency and the reflection coefficient amplitude of the cavity has been observed according to the bias voltage applied. Additional work is required to further investigate the effect of the active PRS on the beam deflection of the antenna cavity.

Conformable and Controllable Radome in X Band using Electromagnetic Band Gap Material

We report the study of the design and the simulation of a conformable and switchable radome in X band (around 10 GHz) based on a controllable electromagnetic band gap material (CEBG) [1-4]. This material consists of parallel periodic metallic wires forming a grid. The introduction of active electronic elements such as PIN diodes or photoconductors, allows the commutation between the electric state of continuous wires and the state of discontinuous ones. We switch from the forbidden gap of an EBG material made of the continuous metallic wires lattice to the forbidden band of the periodic discontinuous wires one, according to the voltage or the light intensity. This structure must present a commutation around 10 GHz and finds various applications in the aeronautic field.

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.

Lenses designed by transformation electromagnetics and fabricated by 3D dielectric printing

Quasi-conformal transformation optics (QCTO) is applied to design electromagnetic lenses for focusing and collimating applications at microwave frequencies. Two devices are studied and conceived by solving the Laplaces equation that describes the deformation of a medium in a space transformation. 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. Prototypes presenting a graded refractive index are fabricated through three-dimensional (3D) polyjet printing using solely dielectric materials. Performed experimental measurements validate the proposed lenses.