Metasurface Antennas: New Models, Applications and Realizations

This paper presents new designs, implementation and experiments of metasurface (MTS) antennas constituted by subwavelength elements printed on a grounded dielectric slab. These antennas exploit the interaction between a cylindrical surface wave (SW) wavefront and an anisotropic impedance boundary condition (BC) to produce an almost arbitrary aperture field. They are extremely thin and excited by a simple in-plane monopole. By tailoring the BC through the shaping of the printed elements, these antennas can be largely customized in terms of beam shape, bandwidth and polarization. In this paper, we describe new designs and their implementation and measurements. It is experimentally shown for the first time that these antennas can have aperture efficiency up to 70%, a bandwidth up to 30%, they can produce two different direction beams of high-gain and similar beams at two different frequencies, showing performances never reached before

A refined stable restriction theorem for vector bundles on quadric threefolds

Let E be a stable rank 2 vector bundle on a smooth quadric threefold Q in the projective 4-space P. We show that the hyperplanes H in P for which the restriction of E to the hyperplane section of Q by H is not stable form, in general, a closed subset of codimension at least 2 of the dual projective 4-space, and we explicitly describe the bundles E which do not enjoy this property. This refines a restriction theorem of Ein and Sols [Nagoya Math. J. 96, 11-22 (1984)] in the same way the main result of Coanda [J. reine angew. Math. 428, 97-110 (1992)] refines the restriction theorem of Barth [Math. Ann. 226, 125-150 (1977)].Comment: Ann. Mat. Pura Appl. 201

Analysis and Design of a Compact Leaky-Wave Antenna for Wide-Band Broadside Radiation

A low-cost compact planar leaky-wave antenna (LWA) is proposed offering directive broadside radiation over a significantly wide bandwidth. The design is based on an annular metallic strip grating (MSG) configuration, placed on top of a dual-layer grounded dielectric substrate. This defines a new two-layer parallel-plate open waveguide, whose operational principles are accurately investigated. To assist in our antenna design, a method-of-moments dispersion analysis has been developed to characterize the relevant TM and TE modes of the perturbed guiding structure. By proper selection of the MSG for a fabricated prototype and its supporting dielectric layers as well as the practical TM antenna feed embedded in the bottom ground plane, far-field pencil-beam patterns are observed at broadside and over a wide frequency range, i.e., from 21.9 GHz to 23.9 GHz, defining a radiating percentage bandwidth of more than 8.5%. This can be explained by a dominantly excited TM mode, with low dispersion, employed to generate a two-sided far-field beam pattern which combines to produce a single beam at broadside over frequency. Some applications of this planar antenna include radar and satellite communications at microwave and millimeter-wave frequencies as well as future 5G communication devices and wireless power transmission systems

Moduli spaces of rank-2 ACM bundles on prime Fano threefolds

cited By (since 1996)1International audienceno abstrac

Overlapped and sequential metasurface modulations for Bi-Chromatic beams generation

This paper describes the generation of directive beams at two different frequencies with the same circular metasurface (MTS) antenna based on a surface wave (SW) excitation. Two methods are presented to achieve the desired bi-chromatic beam operation. The first one consists in mathematically superimposing two MTS modulations, each one matched to the SW wavelength at a different frequency. In the second method, the period of the MTS modulation matches the SW wavelengths at two different frequencies in two different regions of the antenna, i.e., close to the center for the high frequency band and close to the periphery for the low frequency band. The first method allows one to have different feed points for each beam in a self-diplexed structure, although it is also possible to use a single feed configuration and a diplexer. The second approach only holds for a single physical feed-point. Numerical and experimental results are shown

Modulated Metasurface Antennas with Enhanced Broadband Response

International audienceThis paper deals with the crucial need of enhancing the gain-bandwidth of typically narrowband modulated metasurface (MTS) antennas. Despite their low- profile and low-mass, modulated MTSs have typically been limited in terms of bandwidth. In broadside MTS antennas, this shortcoming stems from the progressive mismatch between the periodicity of the modulation (usually constant) and the wavenumber of the dispersive surface wave (SW). Here, an optimization scheme is introduced for the periodicity function, which is described as a piecewise monotonically increasing function along the antenna radius. The variable period leads to the generation of annular active regions, where the SW wavenumber matches the local periodicity, and a strong radiation occurs at the prescribed frequency. On the other hand, outside the annular region the SW weakly interacts with the MTS modulation. This works shows that the proposed method can considerably extend the bandwidth of MTS antennas. © 2021 EurAAP

Perfect non-specular reflection with polarization control by using a locally passive metasurface sheet on a grounded dielectric slab

This paper investigates the conditions for a perfect anomalous reflection through a modulated metasurface consisting of a metallic cladding printed over a grounded slab. Differently to what has been previously published, the problem is rigorously addressed by modeling the metallic cladding through an equivalent penetrable impedance and accounting for the grounded slab through the problem's Green's function. It is shown that without polarization transformation, the exact solution exists only for the special case of retroreflection, and, in that case, it can be done simultaneously for the two orthogonal polarizations, with an arbitrary phase shift among the two. On the other hand, changing the polarization of the reflected wave allows one to find an exact solution for arbitrary combinations of incidence and reflection angles. The exact solution is found by imposing that the induced currents radiating with the Green's function of the background problem simultaneously create the desired reflected beam and cancel the specular reflection from the grounded slab. This approach leads to the derivation of a closed-form expression for the homogenized penetrable impedance profile providing perfect anomalous reflection, i.e., ensuring the vanishing of all the coefficients of the waves associated with unwanted diffraction orders, including the specular reflected wave and the evanescent waves. This result is of great practical interest, since the derived penetrable impedance profile can be readily implemented through a simple distribution of metallic patches. The feasibility of this approach is verified through full wave simulations of both the ideal impedance and the patch-based structure, which confirm the effectiveness of the proposed solution

Design Methodologies for Dual-band Modulated Metasurface Antennas

This paper presents two different design methodologies to cope with the somehow unexplored design of dual-band modulated metasurface (MTS) antennas with circular shape. In the first approach, one overlays two different modulations. Each modulation is appropriately chosen to provide a broadside beam for one of the bands and a very weak radiation for the other frequencies. The second approach builds on the active region modulated MTS concept, recently applied to broadband designs. In this case, the periodicity of the modulation at the central region of the aperture is selected to radiate at the high frequency band. In turn, a larger periodicity in the outer annular region provides the broadside beam at the low frequency band. Both approaches are compared and their advantages and drawbacks, discussed

Modulated Metasurface Antennas with Enhanced Broadband Response

This paper deals with the crucial need of enhancing the gain-bandwidth of typically narrowband modulated metasurface (MTS) antennas. Despite their low- profile and low-mass, modulated MTSs have typically been limited in terms of bandwidth. In broadside MTS antennas, this shortcoming stems from the progressive mismatch between the periodicity of the modulation (usually constant) and the wavenumber of the dispersive surface wave (SW). Here, an optimization scheme is introduced for the periodicity function, which is described as a piecewise monotonically increasing function along the antenna radius. The variable period leads to the generation of annular active regions, where the SW wavenumber matches the local periodicity, and a strong radiation occurs at the prescribed frequency. On the other hand, outside the annular region the SW weakly interacts with the MTS modulation. This works shows that the proposed method can considerably extend the bandwidth of MTS antennas

Overlapped and sequential metasurface modulations for Bi-Chromatic beams generation

International audienceThis paper describes the generation of directive beams at two different frequencies with the same circular metasurface (MTS) antenna based on a surface wave (SW) excitation. Two methods are presented to achieve the desired bi-chromatic beam operation. The first one consists in mathematically superimposing two MTS modulations, each one matched to the SW wavelength at a different frequency. In the second method, the period of the MTS modulation matches the SW wavelengths at two different frequencies in two different regions of the antenna, i.e., close to the center for the high frequency band and close to the periphery for the low frequency band. The first method allows one to have different feed points for each beam in a self-diplexed structure, although it is also possible to use a single feed configuration and a diplexer. The second approach only holds for a single physical feed-point. Numerical and experimental results are shown. © 2021 Author(s)