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The increasing demand for capacity in modern communication systems has made it essential to transition to higher frequencies. With the use of millimeter and sub-millimeter bands, the increase in link losses enforces the use of more directive, precisely pointed, and low-loss antennas. The upcoming of large satellite constellations and the need for ubiquitous connectivity also calls for terminals that are capable of fast pointing., Part of ISBN 9789463968119

In this paper a simple and efficient ray-tracing model is presented to evaluate two-dimensional (2D) multilayer dielectric lenses combined with arrays. The proposed algorithm is capable of accurately evaluating the reflection and absorption losses of the lens. Two examples have been simulated with the proposed algorithm and compared with a commercial full-wave simulator. We demonstrate that the proposed method provides a very good agreement with the simulations, reducing considerably the computation time, and thus offering an effective tool for design optimization., Part of proceedings ISBN: 978-88-31299-09-1QC 20240517

The geodesic Luneburg lens has been revisited as a suitable solution for applications requiring directive beams in the millimeter waveband. Among its advantages, its rotational symmetry and high efficiency stand out. However, one of its drawbacks is the need for a certain height to produce the desired focusing properties of the lens. Here, we propose a low-profile solution based on rotationally symmetric ridges that mimic, similar to geodesic lenses, the effective refractive index of a Luneburg lens. Moreover, we show that both rectangular and trapezoidal ridges perform similarly, opening the possibility for other manufacturing techniques. We demonstrate this concept with a prototype that is fully metallic and provides a scanning range of +/- 62 degrees over a broadband of operation, from 24 to 34 GHz. In this prototype, the height of the lens is 18 times more compact than the original Rinehart-Luneburg lens, allowing the lens to be vertically stacked, which is beneficial, for example, for producing linear arrays. This technique could be used to produce other type of lenses., QC 20240715

This paper evaluates the suitability of additive manufacturing, with AlSi10Mg using the Laser Powder-Bed Fusion (LPBF) technique, for geodesic lens antennas. This evaluation is carried out with three different geodesic lens antennas operating in Ka- V- and G-band. In the Ka-band, an elliptically-compressed geodesic lens antenna was designed, manufactured and tested; in the V-band, the experimental results of a geodesic lens array antenna composed of four elements are shown. These two designs were manufactured monolithically to avoid leakage and misalignment between the plates. Finally, the challenges of additive manufacturing at G-band are discussed. A dual-polarized geodesic Luneburg lens antenna working at 122.5 GHz has been produced in three parts, so polishing can be carried out to reduce the surface roughness. The overall results corroborate that additive manufacturing with the LPBF technique is a promising method to produce metal-only solutions for geodesic lens antennas in the millimetre-wave regime., QC 20240520Part of ISBN 978-883129909-1

In millimeter-wave applications, it is essential to use highly directional and steerable antennas. Phased array antennas are the most common choice, but they have restricted scanning coverage because of their effective aperture. To enhance the scanning coverage, a dielectric lens can be placed on top of the array. However, full-wave simulations require a lot of computing time to simulate this type of structure. In this work, a two-dimensional ray-tracing model has been adapted and improved to efficiently compute the radiation pattern of arrays combined with multilayered dielectric radomes for satellite communications applications. Moreover, this model can also calculate the absorption and reflection losses and the transmitted power required to comply with the regulatory mask. This model has been used to design a lens that increases the scanning range of an array while maintaining a maximum height and ensuring that it complies with the regulatory masks for satellite communications., QC 20240520Part of ISBN 978-88-31299-09-1

This paper investigates the dispersion properties exhibited by three different three-dimensional (3D) periodic arrangements of metallic spheres with the following underlying lattices: simple cubic (sc), body-centered cubic (bcc) and face-centered cubic (fcc) lattice. Their Brillouin zone (BZ) and the corresponding irreducible BZ are introduced. We then examine the dispersion properties along the edges of their respective irreducible BZs. The findings demonstrate that structures with a non-sc arrangement and higher symmetry can improve design versatility while simultaneously reducing the anisotropy of the structure and broadening the operating frequency range. These advantages are beneficial for the development of 3D graded-index (GRIN) lenses., QC 20240521Part of ISBN 978-88-31299-09-1

We propose the use of a generalized ray-tracing model to design geodesic lens array antennas. This model is capable of computing the radiation patterns and taking into account losses due to finite conductivity and surface roughness, which are essential when producing prototypes as single monolithic pieces. The ray-tracing model is used to design a modified Rinehart-Luneburg lens that shows very good agreement with simulations while significantly decreasing computation time. The profile of the lens is designed in such a way that it can be vertically stacked in an array and produced as a single piece. The lens array antenna is manufactured as a single monolithic piece using the laser powder-bed fusion technique. The tests of this prototype validate the use of additive manufacturing for geodesic lens antennas operating in V-band., QC 20240521Part of ISBN 978-883129909-1

Fully metallic geodesic lens antennas are popular for millimeter-wave band applications due to their simplicity, robustness, and low loss. Here, we report the experimental results of a geodesic lens array antenna, which was specifically designed to be additive-manufactured in one single piece using laser powder-bed fusion (LPBF). LPBF in aluminum alloy AlSi10Mg is able to produce high conductivity and relatively low surface roughness, so the antenna is highly directive and efficient. In addition, LPBF increases the robustness of the design since the lens array is monolithic, i.e., the risks associated with the assembly, including misalignments and undesired air gaps between pieces, are totally eliminated., QC 20231121

The Physical Optics (PO) method is used to derive simplified expressions to compute the radiation electric fields of planar graded-index and geodesic lenses based on a parallel-plate waveguide (PPW) implementation. If the PO method is combined with ray-tracing (RT) techniques, the resulting RT-PO procedure is capable of computing radiation patterns and gain of the PPW-based lens antennas when their apertures have a general shape and the electric field is vertically polarized. The RT-PO method is validated by comparing it with the full-wave simulation results of the commercial software ANSYS HFSS for three application cases. The results show that the RT-PO approach is not only very efficient from a computational point of view but also accurate, thus being a very convenient analysis/design tool for this kind of antenna., QC 20240711

Periodic structures are widely used in the design of microwave devices, such as filters and lenses [1, 2]. By altering the periodic element arrangements or their geometric parameters, the wave propagation properties through the structure can be manipulated to realize different functions. The dispersion diagram, which describes the relationship between wavevector components and frequency, is commonly employed to analyze the behavior of the phase/group velocities in periodic structures. In the engineering community, two-dimensional periodic structures have received significant attention, and structures arranged in rectangular and non-rectangular lattices have been investigated [3]. Additionally, three-dimensional (3D) periodic structures arranged in a simple cubic lattice have been studied, but limited efforts have been invested into other lattice arrangements possible in 3D periodic structures. In this contribution, we investigate the dispersion properties of 3D periodic structures with different lattice arrangements and provide detailed analysis steps. Specifically, the simple cubic, body-centered cubic, and face-centered cubic lattices are taken as examples to demonstrate our proposed analysis. Figure 1 illustrates these lattices and their respective smallest geometrical unit cells [4]. The setting of lattice points represents the underlying geometry of periodic structures. In this study, the connection between the lattices in the real and wavevector space is also shown. The smallest unit cell in the wavevector space that describes the full symmetry of the lattice is known as the Brillouin zone (BZ). By considering the symmetry of the smallest unit cell and the real periodic element, the BZ can be reduced further to the irreducible BZ to simplify the analysis. The dispersion properties of periodic structures can then be analyzed by checking the dispersion diagrams within the irreducible BZ, or even solely along its boundaries. We further compare the dispersion diag, Part of proceedings ISBN: 979-8-3503-2058-9QC 20240408

It is demonstrated that combining phased array antennas with dielectric lenses constitutes a suitable solution to increase the energy efficiency in next-generation communication systems. A dielectric lens is designed to increase the gain of an array antenna working in the 3GPP n257 band (26.5–29.5 GHz). The simulated results demonstrate that the dielectric lens increases the gain between 0.4 and 1.3 dB in a large scanning range from 0° to 60° at 28 GHz; meaning that the output RF power can be decreased by up to 26% for a same equivalent isotropic radiated power required from the base station., QC 20230913

In this article, we propose an innovative concept to realize flexible and cost-effective array antenna systems for next generation communication systems. The idea is to tailor the performance of an antenna array to different use case scenarios by applying a customized dielectric lens placed in front of the array. By combining a lens with an array, we can improve certain performance properties of the antenna system and adapt it for unique site locations and requirements. Moreover, the lens may also act as a radome, providing mechanical protection from environmental conditions. This study consists of exploring the possibilities of using a lens to increase the gain of the antenna in certain directions: scanning range close to broadside (from 0 degrees to 30 degrees), and extreme scanning ranges (from 60 degrees to 80 degrees)., Part of ISBN 978-88-31299-07-7QC 20230911

Here, we propose a generalized ray-tracing (RT) model to accurately compute the radiation patterns and radiation efficiency of lossy non-rotationally symmetric geodesic lens antennas. The RT model uses geometrical optics to obtain the ray paths from the source to the aperture, ray tube theory to calculate the field amplitude distribution, and Kirchhoff's diffraction formula to compute the radiation pattern. Losses in geodesic lenses are mainly produced by the finite conductivity and roughness of the metallic plates. These losses are added to the calculation of the radiation pattern to estimate the radiation efficiency of the antenna. To demonstrate the accuracy of the proposed RT model, a geodesic half-Maxwell fish-eye lens is designed. Radiation patterns, scan losses, and radiation efficiency are calculated. These results agree well with those computed by full-wave simulations., Part of ISBN 978-88-31299-07-7QC 20230911

Antennas in emerging millimeter-wave (mm-wave) applications are often required to have low losses and produce a steerable directive beam. These properties are achievable with fully metallic geodesic Luneburg lens antennas. In this communication, we report the first experimental verification of a geodesic Luneburg lens antenna in the V-band. The designed lens antenna is fed with 13 waveguides providing beam switching capability in a 110?degrees range. The lens is implemented in the parallel plate waveguide (PPW) technology. The antenna is manufactured in two pieces, and a tolerance analysis indicates that gaps between the pieces can cause a severe performance degradation. Based on this tolerance analysis, two measures are taken to alleviate the manufacturing tolerances for the prototype. First, electromagnetic band gap (EGB) structures are placed around the feeding waveguides. Second, the electrical contact between the two pieces is improved in critical regions. Two prototypes are manufactured, one without and one with the extra measures implemented. The measured radiation patterns of the prototype without these measures have high side lobes and low realized gain compared with the simulation. The measurements of the robust version of the prototype agree well with the simulations and demonstrate the applicability of geodesic Luneburg lens antennas for applications in the V-band., QC 20230630

Antennas for future communication systems are required to be highly directive and steerable to compensate for the high path loss in the millimeter-wave band. In this work, we propose a linear array of modulated geodesic Luneburg lens (the so-called water drop lens) antennas operating at 56-62 GHz. The lens array antenna features 2-D beam scanning with low structural complexity. The lenses are fully metallic and implemented in parallel plate waveguides (PPWs), meaning that they are highly efficient. Each lens is fed with 13 rectangular waveguides surrounded by glide-symmetric holes to suppress leakage. The lenses provide 110? beam coverage in the H-plane with scan losses below 1 dB. In order to scan in the E-plane, we use a feeding network based on a 1:4 power divider and three phase shifters. In this configuration, the array can scan 60? in the E-plane, albeit with higher scanning losses than in the H-plane. The lens array is manufactured and a good agreement between simulated and experimental results is obtained., QC 20230510

The Physical Optics (PO) method is used to derive simplified expressions to compute the radiation electric fields of planar graded-index and geodesic lenses based on a parallel-plate waveguide (PPW) implementation. If the PO method is combined with ray-tracing (RT) techniques, the resulting RT-PO procedure is capable of computing radiation patterns and gain of the PPW-based lens antennas when their apertures have a general shape and the electric field is vertically polarized. The RT-PO method is validated by comparing it with the full-wave simulation results of the commercial software ANSYS HFSS for three application cases. The results show that the RT-PO approach is not only very efficient from a computational point of view but also accurate, thus being a very convenient analysis/design tool for this kind of antenna.

This thesis focuses on the understanding and computation of the dispersion properties of periodic structures possessing higher symmetries with the multimodal transfer matrix method (MMTMM). Periodic structures with higher symmetries are invariant after additional symmetry operations over the translation operation. To demonstrate the potential of the MMTMM, three structures with spatial higher symmetries are proposed and their operation explained based on the constituent modes. In this thesis, I propose, analyze and explain the operation of two structures possessing glide symmetry and one with twist symmetry. Glide-symmetric structures remain invariant after a mirroring and a translation whereas twist-symmetric structures remain invariant after n rotations and translations. These structures inherently have low dispersion due to the interactions of the fundamental mode with higher order modes. The MMTMM has been implemented in order to efficiently compute the complex propagation constant of these structures. This is a hybrid method that models a unit cell as a multiport network. Each port accounts for one mode, so the coupling between modes is considered. Commercial software is used to compute the ABCD-matrix, then post-processing is used to get both the phase and attenuation constant due to material losses, electromagnetic bandgaps and/or radiation. This method permits the study of complex structures while enabling a fundamental understanding of the modes that contribute to the dispersion properties, as well as their interactions. The first periodic structure analyzed in this thesis is a dielectric-filled corrugated waveguide. It allows the propagation of a backward mode in a wide frequency band. A discussion on the convergence of the method concludes that it is needed families of TE/TM modes with the same number of variations in the x direction. The second structure is a glide-symmetric dielectric unit cell placed in a parallel plate waveguide. This unit cell can, QC 20220926

This article summarizes the recently discovered opportunities of geodesic lenses for producing high-performing antennas for 5G/6G communications. First, we explain the operation of these lenses based on Geometrical Optics with rays that follow "the shortest optical path" on the geodesic surface. Also, we explain the connection between geodesic lenses and rotationally symmetric graded-index lenses. Generally, geodesic lenses can be implemented without the need of dielectric materials, resulting in very efficient devices constructed with a fully-metallic configuration. When combined with a feeding network and a radiating transition, such as a flare or a leaky wave, they can produce a multiple-beam lens antenna, of interest for applications requiring one-dimensional (e.g., azimuthal) coverage diversity such as in cell tower communication systems. Prototypes of these antennas have been recently tested, demonstrating remarkable performance in the Ka-band, part of which is considered for 5G. At high operational frequencies allocated for 5G/6G, geodesic lenses offer an opportunity to produce cost-effective antenna solutions with high directivity, high efficiency and spatial diversity through multiple beams., QC 20220309

The Multimodal Transfer Matrix Method (MMTMM) is a hybrid approach that efficiently computes the dispersion relation of a periodic structure. It is able to retrieve both the phase shift and attenuation constant of any arbitrary structure susceptible to be analyzed by means of commercial simulators. Here, we propose the use of this method in order to get a physical insight of periodic structures possessing higher symmetries. The MMTMM is here explained and corroborated with two different structures: a glide-symmetric dielectric-filled corrugated rectangular waveguide and a three-fold twist-symmetric bricks embedded in a dielectric waveguide. The first structure allows for the propagation of backward modes below the hollow waveguide cut-off frequency, whereas the second one has handedness selection., Part of proceedings: ISBN 978-88-31299-04-6QC 20220826

In this work, we design a planar half-Luneburg lens antenna. The gradient of refractive index is realized using a dielectric slab periodically loaded with air-cavities of varying size. The cavities are glide-symmetrically arranged. It is demonstrated that by introducing glide symmetry, the bandwidth and range of realizable refractive indices are increased compared to a non-glide-symmetric structure. The lens antenna operates from 22 to 32 GHz and can scan its directive beam over a 50 degree range in the H-plane. The side lobe level in this scan range is lower than -10 dB throughout the band., QC 20220812Part of proceedings: ISBN 978-88-31299-04-6

This paper presents a model developed to numerically determine the radiation pattern presented by a given geodesic lens. A simplified model describing the trajectory of a TEM-mode wave through the lens was required as a time-efficient alternative to commercial software. Geometrical optics have been used to approximate the ray trajectory from the source to the aperture of the lens. The power conservation in ray tubes is then used to evaluate the amplitude of the electric field in the aperture, knowing the distribution at the source. The Kirchhoff diffraction formula is finally numerically approximated to evaluate the farfield. Three examples have been simulated with our algorithm and compared with full-wave simulations. We demonstrate that our assumptions provide a good agreement with full-wave simulation while reducing significantly the computation time, thus providing an efficient method for design optimization. Most notably, this more general formulation may be extended to non-rotationally symmetric lenses., QC 20220812Part of proceedings: ISBN 978-88-31299-04-6

Here, we propose a modulated geodesic lens antenna array in E-band (56-62 GHz), which has scanning abilities in both azimuth and elevation. The array consists of four lens antenna elements, and each lens antenna produces 13 independent beams that cover 110 degrees in the H-plane with scan losses below 1 dB. The array is fed with a 1:4 power divider comprising three phase shifters to scan in the E-plane. The distance between lenses in the E-plane is 0.7 wavelengths at 60 GHz. The E-plane coverage is 60 degrees with scan losses around -2.2 dB. The maximum realized gain varies from 20.8 to 24.1 dB across the frequency band., QC 20230316

Connecting networks for two-dimensional beamforming matrices are discussed. They provide a suitable interconnection between the output ports of a Butler matrix and antenna array ports, transforming a square (and more generally, rectangular) lattice of beams into a triangular lattice of beams. This change in lattice improves the crossover between beams, reducing gain roll-off over the field of view for a given multiple fixed beam coverage. A general description of the concept is provided and numerical results are reported, which confirm a reduction in crossover level between 1 and 1.5 dB. The proposed solution is further validated through the design and test of a 4 × 4 open-ended waveguide array in K-band. The connecting network has a length of 70 mm, compared to 226 mm for the 2D Butler matrix, with a design frequency of 19.55 GHz. Good agreement is found between simulated and measured data. The desired triangular lattice of beams is confirmed with the measured multiple beams. This solution is of interest for multiple-beam millimeter-wave communication systems, considered for next generation of terrestrial and non-terrestrial networks., QC 20240807

We propose a circular twist-symmetric dielectric waveguide that is polarization-selective. In the practical implementation of optical fibers, a selective circular polarization is more convenient than its linearly polarized counterpart where previous knowledge of the emitted polarization from the transmitter is unknown. The analysis of the waveguide was conducted with three methods: an eigenmode approach, simulation of a truncated structure, and the so-called multimodal transfer-matrix method (MMTMM). The presented simulations demonstrate that the operational band can be manipulated by tuning the parameters of the structure. Furthermore, the MMTMM allows for a direct and accurate calculation of the attenuation constant of the rejected circular polarization., QC 20210727

We propose a circular twist-symmetric dielectric waveguide that is polarization-selective. In the practical implementation of optical fibers, a selective circular polarization is more convenient than its linearly polarized counterpart where previous knowledge of the emitted polarization from the transmitter is unknown. The analysis of the waveguide was conducted with three methods: an eigenmode approach, simulation of a truncated structure, and the so-called multimodal transfer matrix method (MMTMM). The presented simulations demonstrate that the operational band can be manipulated by tuning the parameters of the structure. Furthermore, the MMTMM allows for a direct and accurate calculation of the attenuation constant of the rejected circular polarization.

This work studies the propagation characteristics of a rectangular waveguide with aligned/ misaligned double-sided dielectric-filled metallic corrugations. Two modes are found to propagate in the proposed double-sided configuration below the hollow-waveguide cutoff frequency: a quasi resonant mode and a backward mode. This is in contrast to the single-sided configuration, which only allows for backward propagation. Moreover, the double-sided configuration can be of interest for waveguide miniaturization on account of the broader band of its backward mode. The width of the stopband between the quasi-resonant and backward modes can be controlled by the misalignment of the top and bottom corrugations, being null for the glide-symmetric case. The previous study is complemented with numerical results showing the impact of the height of the corrugations, as well as the filling dielectric permittivity, on the bandwidth and location of the appearing negative effective-permeability band. The multi-modal transmission-matrix method has also been employed to estimate the rejection level and material losses in the structure and to determine which port modes are associated with the quasi-resonant and backward modes. Finally, it is shown that glide symmetry can advantageously be used to reduce the dispersion and broadens the operating band of the modes

In this letter, we propose and study a 2-D glide-symmetric dielectric periodic structure. We demonstrate that glide symmetry broadens the bandwidth of operation and achieves lower effective refractive indices when compared to non-glide configurations. These two properties are beneficial for producing graded-index lens antennas. To demonstrate the potential of the proposed unit cell, we designed a Luneburg lens operating in the K- and K-a-bands. The lens was manufactured with conventional additive manufacturing and it has a potential use for future wireless communications given its low-cost and low-profile., QC 20211206

This work studies the propagation characteristics of a rectangular waveguide with aligned/misaligned double-sided dielectric-filled metallic corrugations. Two modes are found to propagate in the proposed double-sided configuration below the hollow-waveguide cutoff frequency: a quasi-resonant mode and a backward mode. This is in contrast to the single-sided configuration, which only allows for backward propagation. Moreover, the double-sided configuration can be of interest for waveguide miniaturization on account of the broader band of its backward mode. The width of the stopband between the quasi-resonant and backward modes can be controlled by the misalignment of the top and bottom corrugations, being null for the glide-symmetric case. The previous study is complemented with numerical results showing the impact of the height of the corrugations, as well as the filling dielectric permittivity, on the bandwidth and location of the appearing negative-effective-permeability band. The multi-modal transmission-matrix method has also been employed to estimate the rejection level and material losses in the structure and to determine which port modes are associated with the quasi-resonant and backward modes. Finally, it is shown that glide symmetry can advantageously be used to reduce the dispersion and broadens the operating band of the modes., QC 20211011

Here, we study the propagation of a twist-symmetric dielectric rod with three different methods: eigenmode solver, multimode Bloch analysis, and scattering parameters of a truncated structure. With the eigenmode analysis, we demonstrate that these structures permit the propagation of circularly polarized modes, and only one of the modes has a stopband in the first Brillouin zone. These results are corroborated with the simulation of a truncated structure, demonstrating that the propagation is only possible for one of the modes at a given frequency band. Finally, the multimode Bloch analysis is used to also characterize the attenuation constant in the stopband., Part of ISBN 978-88-31299-02-2QC 20210830