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Equivalent Planar Lens Ray-Tracing Model to Design Modulated Geodesic Lenses Using Non-Euclidean Transformation Optics
European Space Agcy, Antenna & Submillimeter Waves Sect, NL-2200 AG Noordwijk, Netherlands..
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.ORCID iD: 0000-0002-7243-6167
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.ORCID iD: 0000-0002-4900-4788
2020 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 68, no 5, p. 3410-3422Article in journal (Refereed) Published
Abstract [en]

This article describes a design procedure that enables a time-efficient evaluation of the focusing properties of modulated geodesic lenses using ray tracing on the equivalent gradient-index planar lens. The method uses transformation optics to define the equivalent planar relative permittivity distribution of axially symmetric surfaces and a ray-tracing model to evaluate the phase distribution in the aperture of the lens. This approach is of interest to optimize modulated geodesic lenses having polynomial profiles, reducing their height while preserving their wideband behavior and wide angular focusing properties. The approach is validated with a specific lens design. The profile is optimized at 30 GHz, while the focusing properties are monitored over the complete Ka up-link frequency band allocated to satellite communications (i.e., 27.5 & x2013;31 GHz). The manufactured prototype produces 21 beams equally spaced every 7.5 & x00B0; over the extended angular range of & x00B1;75 & x00B0;. The ray-tracing model results are compared in detail with the corresponding full-wave model results and experimental data. The manufactured design has return loss better than 15 dB over a fractional frequency bandwidth larger than 30 & x0025;, in line with the predictions. Excellent scanning properties are demonstrated over an angular range of & x00B1;60 & x00B0; with scan losses below 1 dB and good pattern stability, including on sidelobe levels. A height reduction by a factor of 4, when compared to a conventional geodesic lens, is demonstrated with this specific design.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC , 2020. Vol. 68, no 5, p. 3410-3422
Keywords [en]
Geodesic lens, Luneburg lens, modulated lens, planar beamformer, transformation optics, true time delay beamforming, wide angular scanning
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-276910DOI: 10.1109/TAP.2020.2963948ISI: 000534640900009Scopus ID: 2-s2.0-85084817542OAI: oai:DiVA.org:kth-276910DiVA, id: diva2:1444688
Note

QC 20200622

Available from: 2020-06-22 Created: 2020-06-22 Last updated: 2022-06-26Bibliographically approved
In thesis
1. Fully metallic antennas for millimeter wave applications
Open this publication in new window or tab >>Fully metallic antennas for millimeter wave applications
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Modern societal demands for a high data throughput, short time latency and low energy consumption are difficult to satisfy using current wirelesscommunication techniques. The carrier frequency of previous wireless communication, such as broadcast, the global system for mobile communication, and wireless local area networks, are in the sub-3 GHz spectrum. Electromagnetic waves in the sub-3 GHz spectrum possess a long wavelength and small free space path loss (FSPL), but with a narrow absolute bandwidth. This absolute bandwidth limits the channel capacity according to Shannon theory. Under the assumption that relative bandwidth is fixed, the absolute bandwidth is proportional to the carrier frequency. That means, wireless communications with high carrier frequency can provide wide bandwidth and large channel capacity. Besides, the sub-3 GHz spectrum is already too crowded to have future advanced wireless communications. Nowadays, it is essential to move carrier frequencies to higher frequency spectrum. The millimeter wave (mmWave) frequency band can provide an extensive bandwidth but suffers high atmospheric attenuation and FSPL. The highattenuation and loss limit the propagation distance of mmWave to a few kilometers. Additionally there is a high attenuation due to precipitation, as the wavelength of mmWaves are of the same order in size as rain drops. Due to these losses, there are restricted applications in the mmWave band used for wireless communications. However, the electromagnetic spectrumshortage encourages new researches to look for solutions overcoming the drawbacks of mmWave.

Specific requirements on antenna designs are imposed by using mmWave communication, including manufacturing costs, integration, efficiency, scanningrange, and directivity. Antennas designed for the mmWave have a small physical size, which requires finer manufacturing resolution and increases manufacturing costs. To compensate for the high FSPL and attenuations, high directive antennas with low side lobe level are favorable. To improve the radiation efficiency, it is preferred to use fully metallic structuresas opposed to structures containing dielectrics for antennas operating in the mmWave range. This thesis investigates the innovative techniques for designing high performance fully metallic antennas in mmWave. Antennas made in gap waveguides and geodesic lens antennas have low manufacturing costs, low loss, and high directivity. The gap waveguide technology can be used to manufacture antennas in separated pieces. These pieces are united together afterwards. The manufacturing cost is reduced in this way. In gap waveguides, the radiation leakages from gaps between separated pieces are prevented using metasurfaces. The research emphasis is placed on the properties of glide-symmetric metasurfaces. Comparing with non-glide metasurfaces, glide-symmetric metasurfaces have an extended electromagnetic bandgap. On the other side, the geodesic lens antenna is designed based on geometrical optics (GO). The graded index lenses can be transformed to geodesic shapes through GO. Since the mmWave presents optical propagation characteristics, GO can be used as a good approximation. A ray-tracing model is developed to calculate the radiation patterns of geodesic lenses and its performance is verified by full wave simulations. Geodesic lens antennas implemented in parallel plate waveguides are in full metal and allow waves to propagate in vacuum or air.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2021. p. 147
National Category
Telecommunications Communication Systems
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-295208 (URN)978-91-7873-869-4 (ISBN)
Public defence
2021-06-08, H1, Teknikringen 33, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20210531

Available from: 2021-05-31 Created: 2021-05-18 Last updated: 2022-07-08Bibliographically approved

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Liao, QingbiQuevedo-Teruel, Oscar

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