151 research outputs found
Multibeam and Beam Scanning With Modulated Metasurfaces
No full textMultibeam and beam-scanning capabilities of metasurface (MTS) antennas using multiple feeds are investigated. The MTS synthesis is performed by direct inversion of an electric field integral equation (EFIE) obtained after expanding the unknown equivalent impedance profile into Fourier-Bessel basis functions. Two approaches are explored. The first one assumes a priori a discrete azimuthal symmetry in the impedance profile, so as to constrain the solution to a subspace which automatically provides multiple beams when illuminated with feeds regularly arranged along azimuth. In the second approach, there are not a priori assumptions on the impedance profile, but the systems of equations corresponding to each beam are stacked and solved simultaneously in the least-squares sense. This second approach can also be used to obtain polarization diversity. More importantly, it also enables continuous beam scanning. The latter functionality is achieved through the generation of two embedded patterns in a common azimuthal window with opposite phase slopes, followed by a continuous phasing of the two feed points. Various designs are presented in this article. All the results are validated with the method of moments (MoM)
Another Field Decomposition for the Transmittance between OAM Antennas
No full textThis paper first provides an intuitive description of the spectral representations for the transmittance between two apertures. Then, two spectral representations of the transmittance between OAM antennas are compared. The first one makes use of the Modified Zernike function and has already been described in a previous publication. The second one is based on the Fourier-Bessel decomposition of the current distribution on the apertures. Both families of expansion functions are orthogonal on a disk and admit a closed form spectrum. In both cases, the transmittance in the far-field can be approximated in closed form if the current distribution is expressed in the basis. However, it is observed that the far-field behavior is fundamentally different, highlighting the complementarity between the two bases
Cosecant Squared pattern synthesis of linear antenna arrays based on an adaptive least Square algorithm
No full textMulti-Feed Metasurface Antennas: Direct Numerical Design and Experimental Validations
No full textThis paper provides new designs and realizations of leaky-wave (LW) metasurface (MTS) antennas fed at multiple points. The design technique is based on the direct integral-equation solution by the Method of Moments (MoM). The unknown is no longer the current distribution, but the impedance profile itself. The method can be used to generate any shaped radiation pattern in amplitude, phase, and polarization, provided that the antenna area and the feeder illumination are consistent with the shape of the desired radiation pattern. The algorithm can also be used to design multi-functional antennas (multibeam, multiband, dual-polarizion, etc). While multiple feeds are traditionally used to implement multiple fonctionnalities, they may also be required for the efficient generation of a single shaped beam, thus leading to a higher surface-wave (SW) to LW conversion efficiency. The present paper shows for the first time, two realizations of MTS design with the integral equation formalism, which require the usage of multiple feeds: a circularly polarized sectoral conical beam and a dual-polarized broadside beam MTS antenna. The good comparison between measurements and numerical predictions shows the effectiveness of the design method
Method of Moments Simulation of Modulated Metasurface Antennas With a Set of Orthogonal Entire-Domain Basis Functions
No full textInternational audienceA family of orthogonal and entire-domain basis functions (named Fourier-Bessel) is proposed for the analysis of circular modulated metasurface (MTS) antennas. In the structures at hand, the MTS is accounted for in the electric field integral equation (EFIE) as a sheet transition impedance boundary condition on the top of a grounded dielectric slab. The closed-form Hankel transform of the Fourier-Bessel basis functions (FBBFs) allows one to use a spectral domain formulation in the method-of-moments (MoM) solution of the EFIE. Moreover, these basis functions are fully orthogonal, which implies that they are able to represent the global evolution of the current distribution in a compact form. FBBFs also present a better filtering capability of their spectrum compared to other well-known orthogonal families such as the Zernike functions. The obtained MoM matrix is sparse and compact, and it is thus very well-conditioned and can be efficiently computed and inverted. The numerical results based on the proposed decomposition are presented and compared with those based on the use of the Gaussian ring basis functions and with the full-wave analysis of MTS antennas implemented with small printed elements. A very good agreement is observed
Fourier-Bessel Basis Functions for the Analysis of Elliptical Domain Metasurface Antenna
No full textA Quasi-Direct Method for the Surface Impedance Design of Modulated Metasurface Antennas
No full textEfficient Tracking of Dispersion Surfaces for Printed Structures using the Method of Moments
No full textThe dispersion surfaces of printed periodic structures in layered media are
efficiently computed using a full-wave method based on the periodic Method of
Moments (MoM). The geometry of the dispersion surface is estimated after
mapping the determinant of the periodic MoM impedance matrix over a range of
frequencies and impressed phase shifts. For lossless periodic structures in the
long-wavelength regime, such as lossless metasurfaces, a tracking algorithm is
proposed to represent the dispersion surface as a superposition of
parameterized iso-frequency curves. The mapping process of the determinant is
accelerated using a specialized interpolation technique with respect to the
frequency and impressed phase shifts. The algorithm combines a fast evaluation
of the rapidly varying part of the periodic impedance matrix and the
interpolation of the computationally intensive but slowly varying remainder.
The mapping is further accelerated through the use of Macro basis functions
(MBFs). The method has been first tested on lossless metasurface-type
structures and validated using the commercial software CST. The specialized
technique enables a drastic reduction of the number of periodic impedance
matrices that needs to be explicitly computed. In the two examples considered,
only 12 matrices are required to cover any phase shift and a frequency band
larger than one octave. An important advantage of the proposed method is that
it does not entail any approximation, so that it can be used for lossy
structure and leaky waves, as demonstrated through two additional examples.Comment: Paper accepted for publication in IEEE Transactions on Antennas and
Propagatio
Sparse-Array Metasurface for Beam Scanning
No full textBeam scanning is traditionally achieved with phased arrays, whose application often faces the challenge of high density of antennas and associated electronic components. Metasurfaces (MTS) allow the tailoring of pencil and shaped beams with a low-profile radiator, but scanning with MTSs remains difficult, e.g., reconfiguring each subwavelength patch of the MTS defeats the initial purpose of simplicity. This communication proposes a novel design approach to beam scanning with surface-wave (SW)-based MTS antennas. Both the feeding and the MTS are made periodic at a scale of a few wavelengths. To avoid grating lobes, the unit cell of the periodic MTS is designed, such that the embedded element pattern (EEP) has a nearly rectangular shape with proper width. The sparsity of the feeding system enables a drastic reduction of the density of electronics at the expense of a smaller field of view. The resulting antenna, demonstrated here in 2-D (uniform antenna versus one space coordinate), has low profile (including the feeder) and enables continuous beam scanning with high gain. With a spacing of two wavelengths between feeds, the scan range is +/−10°. The MTS is first designed at the surface impedance level, and the resulting structure has then been validated through full-wave simulation of a MTS implemented with subwavelength patches. Numerical analysis versus frequency indicates a pattern bandwidth of the order of 5%
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