| 1. |
- Alex-Amor, Antonio, et al.
(författare)
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Dispersion Analysis of Periodic Structures in Anisotropic Media : Application to Liquid Crystals
- 2022
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Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 70:4, s. 2811-2821
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Tidskriftsartikel (refereegranskat)abstract
- This article presents an efficient method to compute the dispersion diagram of periodic and uniform structures with generic anisotropic media. The method takes advantage of the ability of full-wave commercial simulators to deal with finite structures having anisotropic media. In particular, the proposed method extends the possibilities of commercial eigenmode solvers in the following ways: 1) anisotropic materials with nondiagonal permittivity and permeability tensors can be analyzed; 2) the attenuation constant can easily be computed in both propagating and stopband regions, and lossy materials can be included in the simulation; and 3) unbounded and radiating structures, such as leaky-wave antennas (LWAs), can be treated. The latter feature may be considered the most remarkable since the structures must be forcefully bounded with electric/magnetic walls in the eigensolvers of most commercial simulators. In this work, the proposed method is particularized for the study of liquid crystals (LCs) in microwave and antenna devices. Thus, the dispersion properties of a great variety of LC-based configurations are analyzed, from canonical structures, such as waveguide and microstrip, to complex reconfigurable phase shifters in ridge gap-waveguide technology and LWAs. Our results have been validated with previously reported works in the literature and with commercial software CST and HFSS.
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| 2. |
- Alex-Amor, Antonio, et al.
(författare)
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Elliptical Glide-Symmetric Holey Metasurfaces for Wideband Anisotropy
- 2020
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Ingår i: 2020 14th European Conference on Antennas and Propagation (EUCAP 2020). - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- This paper presents a mode-matching technique to study the dispersive features of periodic structures composed of glide-symmetric elliptical holes. As a difference from purely numerical methods, our formulation provides physical insight on the Floquet harmonics. At the same time, the computational cost is reduced compared to general purpose commercial software. The fields inside the holes are described by means of Mathieu functions and subsequently used to compute the full 2-D dispersion diagrams. With the presented analysis, we demonstrate that glide-symmetric periodic structures with elliptical holes offer anisotropic refractive indexes over a wide range of frequencies.
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| 3. |
- Alex-Amor, Antonio, et al.
(författare)
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Glide-Symmetric Metallic Structures With Elliptical Holes for Lens Compression
- 2020
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Ingår i: IEEE transactions on microwave theory and techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 68:10, s. 4236-4248
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we study the wave propagation in a metallic parallel-plate structure with glide-symmetric elliptical holes. To perform this study, we derived a mode-matching technique based on the generalized Floquet theorem for glide-symmetric structures. This mode-matching technique benefits from a lower computational cost since it takes advantage of the glide symmetry in the structure. It also provides physical insight into the specific properties of Floquet modes propagating in these specific structures. With our analysis, we demonstrate that glide-symmetric structures with periodic elliptical holes exhibit an anisotropic refractive index over a wide range of frequencies. The equivalent refractive index can be controlled by tuning the dimensions of the holes. Finally, by combining the anisotropy related to the elliptical holes and transformation optics, a Maxwell fish-eye (MFL) lens with a 33.33% size compression is designed. This lens operates in a wideband frequency range from 2.5 to 10 GHz.
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| 4. |
- Alex-Amor, Antonio, et al.
(författare)
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Wave Propagation in Periodic Metallic Structures with Equilateral Triangular Holes
- 2020
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies wave propagation in a periodic parallel-plate waveguide with equilateral triangular holes. A mode-matching method is implemented to analyze the dispersion diagram of the structure possessing glide and mirror symmetries. Both structures present an unexpected high degree of isotropy, despite the triangle not being symmetric with respect to rotations of 90 degrees. We give some physical insight on the matter by carrying out a modal decomposition of the total field on the hole and identifying the most significant modes. Additionally, we demonstrate that the electrical size of the triangular hole plays a fundamental role in the physical mechanism that causes that isotropic behavior. Finally, we characterize the influence of the different geometrical parameters that conform the unit cell (period, triangle size, hole depth, separation between metallic plates). The glide-symmetric configuration offers higher equivalent refractive indexes and widens the stopband compared to the mirror-symmetric configuration. We show that the stopband is wider as the triangle size is bigger, unlike holey structures composed of circular and elliptical holes where an optimal hole size exists.
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| 5. |
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| 6. |
- Padilla, Pablo, et al.
(författare)
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Broken Glide-Symmetric Holey Structures for Bandgap Selection in Gap-Waveguide Technology
- 2019
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Ingår i: IEEE Microwave and Wireless Components Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1531-1309 .- 1558-1764. ; 29:5, s. 327-329
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, we propose a new technique to tune the bandgap in gap-waveguide technology based on broken glide-symmetric holey structures. We demonstrate that breaking the glide-symmetry in a proper manner provokes the presence of a passband within the bandgap due to the frequency sweep of the second propagating mode. This passband generates field leakage in the gap that is translated into a filtering property. This filtering effect may be used to reduce or eliminate filters in large complex devices. In order to avoid undesired coupling due to the leakage from the air gap between the plates, an absorbing sheet is proposed to dissipate the undesired fields. This idea has been numerically studied and experimentally validated with a specific design, a WR15-size gap-waveguide prototype with glide-symmetric holes with filtering properties.
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| 7. |
- Padilla, Pablo, et al.
(författare)
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Glide-symmetric printed corrugated transmission lines with controlable stopband
- 2019
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Ingår i: 13th European Conference on Antennas and Propagation, EuCAP 2019. - : Institute of Electrical and Electronics Engineers (IEEE). - 9788890701887
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Konferensbidrag (refereegranskat)abstract
- Here, we demonstrate that the dispersion properties of printed lines can be controlled by using glide symmetry. Glide symmetry is introduced by means of corrugations in the printed lines. The glide-symmetric configuration provides a more linear propagation constant, avoiding the presence of stopband between first and second propagating modes. Additionally, the breakage of the glide-symmetric geometry introduces a tunable stopband that can be used for filtering.
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| 8. |
- Palomares-Caballero, Angel, et al.
(författare)
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Twist and Glide Symmetries for Helix Antenna Design and Miniaturization
- 2019
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Ingår i: Symmetry. - : MDPI. - 2073-8994. ; 11:3
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Tidskriftsartikel (refereegranskat)abstract
- Here we propose the use of twist and glide symmetries to increase the equivalent refractive index in a helical guiding structure. Twist- and glide-symmetrical distributions are created with corrugations placed at both sides of a helical strip. Combined twist-and glide-symmetrical helical unit cells are studied in terms of their constituent parameters. The increase of the propagation constant is mainly controlled by the length of the corrugations. In our proposed helix antenna, twist and glide symmetry cells are used to reduce significantly the operational frequency compared with conventional helix antenna. Equivalently, for a given frequency of operation, the dimensions of helix are reduced with the use of higher symmetries. The theoretical results obtained for our proposed helical structure based on higher symmetries show a reduction of 42.2% in the antenna size maintaining a similar antenna performance when compared to conventional helix antennas.
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