Lens Antennas: Fundamentals and Present Applications

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Lens antennas are commonly englobed in a more general type of antennas, named aperture antennas. As their name indicates, they make use of a lens to modify the field distribution at the aperture of the antenna, which is typically fed by a single source. The lens is employed to transform the waves arriving from the source into a desired radiation pattern. Commonly, the desired radiation pattern is a directive beam in a given direction. However, similar to arrays, reflectors or leaky wave antennas, the goal changes depending on the application. For example, other desired features may be to produce multiple beams, or a broad beam-width.
Lenses were more commonly employed in optical applications. For this reason, most of the nomenclature comes from optics, and they are evaluated with rays theory. In this sense, the performance of the lens is conventionally described in terms of aberrations. An aberration is a failure of the rays to converge at the desired focus. This failure must be due to a defect or an improper design. Aberrations are classified as chromatic or monochromatic, depending on whether or not they have a frequency dependence. There are five monochromatic aberrations: spherical aberration, coma, astigmatism, Petzval field curvature, and distortion. However, this is not a common nomenclature for antenna designers in the radio-frequency and microwave regimes. In these regimes, the rays are substituted by electromagnetic fields, and the designers evaluate their antennas in terms of directivity, gain, efficiency, side lobe levels, cross polarization levels, etc. Therefore, there is a communication gap between both communities: optics and microwaves. In the THz regime, which is in between these two communities, researchers must understand both nomenclatures
In this talk, I will explain the operation of lens antennas, their potential, and two innovative techniques that have become very important in recent years. The first technique is transformation optics, which can be employed to produce three-dimensional directive lenses. The second one is metasurfaces, which can be used to produce low-cost and planar two-dimensional lenses. In the case of metasurfaces, fully metallic solutions are possible, which is a clear advantage in terms of losses. However, with the available technology, metasurfaces are only able to scan in one single plane. Finally, we introduce the concept of higher symmetries, that can be employed to enhance the bandwidth of conventional metasurfaces, or to increase their equivalent refractive indexes.

 



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  • Date: 09 Nov 2020
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  Speakers

Oscar Quevedo-Teruel Oscar Quevedo-Teruel of KTH Royal Institute of Technology

Topic:

Lens Antennas: Fundamentals and Present Applications

Abstract:


Lens antennas are commonly englobed in a more general type of antennas, named aperture antennas. As their name indicates, they make use of a lens to modify the field distribution at the aperture of the antenna, which is typically fed by a single source. The lens is employed to transform the waves arriving from the source into a desired radiation pattern. Commonly, the desired radiation pattern is a directive beam in a given direction. However, similar to arrays, reflectors or leaky wave antennas, the goal changes depending on the application. For example, other desired features may be to produce multiple beams, or a broad beam-width.
Lenses were more commonly employed in optical applications. For this reason, most of the nomenclature comes from optics, and they are evaluated with rays theory. In this sense, the performance of the lens is conventionally described in terms of aberrations. An aberration is a failure of the rays to converge at the desired focus. This failure must be due to a defect or an improper design. Aberrations are classified as chromatic or monochromatic, depending on whether or not they have a frequency dependence. There are five monochromatic aberrations: spherical aberration, coma, astigmatism, Petzval field curvature, and distortion. However, this is not a common nomenclature for antenna designers in the radio-frequency and microwave regimes. In these regimes, the rays are substituted by electromagnetic fields, and the designers evaluate their antennas in terms of directivity, gain, efficiency, side lobe levels, cross polarization levels, etc. Therefore, there is a communication gap between both communities: optics and microwaves. In the THz regime, which is in between these two communities, researchers must understand both nomenclatures
In this talk, I will explain the operation of lens antennas, their potential, and two innovative techniques that have become very important in recent years. The first technique is transformation optics, which can be employed to produce three-dimensional directive lenses. The second one is metasurfaces, which can be used to produce low-cost and planar two-dimensional lenses. In the case of metasurfaces, fully metallic solutions are possible, which is a clear advantage in terms of losses. However, with the available technology, metasurfaces are only able to scan in one single plane. Finally, we introduce the concept of higher symmetries, that can be employed to enhance the bandwidth of conventional metasurfaces, or to increase their equivalent refractive indexes.

Fig. 1: Transformation of a cylindrical wave into a plane wave by using a convex lens represented with rays and waves.

Biography:

Oscar Quevedo-Teruel is a Senior Member of the IEEE. He received his Telecommunication Engineering Degree from Carlos III University of Madrid, Spain in 2005, part of which was done at Chalmers University of Technology in Gothenburg, Sweden. He obtained his Ph.D. from Carlos III University of Madrid in 2010 and was then invited as a postdoctoral researcher to the University of Delft (The Netherlands). From 2010-2011, Dr. Quevedo-Teruel joined the Department of Theoretical Physics of Condensed Matter at Universidad Autonoma de Madrid as a research fellow and went on to continue his postdoctoral research at Queen Mary University of London from 2011-2013.
In 2014, he joined the Division for Electromagnetic Engineering in the School of Electrical Engineering and Computer Science at KTH Royal Institute of Technology in Stockholm, Sweden where he is an Associate Professor and Director of the Master Programme in Electromagnetics Fusion and Space Engineering. He has been an Associate Editor of the IEEE Transactions on Antennas and Propagation since 2018 and is the founder and editor-in-chief of the EurAAP journal Reviews of Electromagnetics since 2020. He was the EurAAP delegate for Sweden, Norway, and Iceland from 2018-2020. He is a distinguished lecturer of the IEEE Antennas and Propagation Society for the period of 2019-2021, and Chair of the IEEE APS Educational Initiatives Programme since 2020.
He has made scientific contributions to higher symmetries, transformation optics, lens antennas, metasurfaces, leaky wave antennas and high impedance surfaces. He is the co-author of 95 papers in international journals and 140 at international conferences.

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