Here, we propose a fully metallic implementation of a Luneburg lens operating at Ka-band with potential use for 5G communications. The lens is implemented with a parallel plate that is loaded with glide-symmetric holes. These holes are employed to produce the required equivalent refractive index profile of a Lune-burg lens. Glide symmetry and inner metallic pins are employed to increase the equivalent refractive index. The lens is fed with rectangular waveguides designed to match the height of the parallel plate, and it is ended with a flare to minimize the reflections.

Glide-Symmetric Fully Metallic Luneburg Lens for 5G Communications at K a -Band

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., 27.5–31 GHz). The manufactured prototype produces 21 beams equally spaced every 7.5° over the extended angular range of ±75°. 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%, in line with the predictions. Excellent scanning properties are demonstrated over an angular range of ±60° 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.

Equivalent Planar Lens Ray-Tracing Model to Design Modulated Geodesic Lenses Using Non-Euclidean Transformation Optics

Multi-beam antennas are critical components in future terrestrial and non-terrestrial wireless communications networks. The multiple beams produced by these antennas will enable dynamic interconnection of various terrestrial, airborne and space-borne network nodes. As the operating frequency increases to the high millimeter wave (mmWave) and terahertz (THz) bands for beyond 5G (B5G) and sixth-generation (6G) systems, quasi-optical techniques are expected to become dominant in the design of high gain multi-beam antennas. This paper presents a timely overview of the mainstream quasi-optical techniques employed in current and future multi-beam antennas. Their operating principles and design techniques along with those of various quasi-optical beamformers are presented. These include both conventional and advanced lens and reflector based configurations to realize high gain multiple beams at low cost and in small form factors. New research challenges and industry trends in the field, such as planar lenses based on transformation optics and metasurface-based transmitarrays, are discussed to foster further innovations in the microwave and antenna research community.

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Quasi-Optical Multi-Beam Antenna Technologies for B5G and 6G mmWave and THz Networks: A Review

An analytical model based on geometrical optics is proposed to design and analyze continuous parallel plate waveguide (PPW) lens-like antennas. The proposed design is based on a transversal PPW section working as a lens-like beamformer. By simplifying the propagation inside this transversal section, a bifocal constrained lens model is first defined; it provides a relevant starting point to design the proposed beamformer. A refined model based on ray tracing and with an enhanced performance prediction is achieved by accounting the wave propagation inside the transversal cavity. The numerical analysis of phase aberrations and radiation demonstrate the performance of the proposed beamformer. The results of the ray-tracing model are in a very good agreement with the corresponding full-wave model, while providing a significant reduction in the computational effort, making the proposed model more suitable for advanced optimization processes.

Analytical Model and Study of Continuous Parallel Plate Waveguide Lens-like Multiple-Beam Antennas

In this paper, shaped continuous parallel plate waveguide delay lenses are proposed. The previous configurations introduced by the authors displayed a residual side lobe imbalance, showing the limitations of elliptical delay lens profiles, derived from a starting bifocal constrained lens. Polynomial profiles are proposed here as a way to enhance the scanning performance and the pattern shape. Optimized configurations demonstrate a reduction in the phase aberration levels over a large scanning range ([−30°, 30°]). The associated radiation patterns demonstrate lower and more balanced first side lobe levels (SLLs) ( $\cong -18$ dB), as compared to the previous elliptical approach ( $\cong -13.2$ dB). A validation has been proposed through the manufacturing and test of a prototype over the down-link Ka-band ([27.5–31] GHz). Excellent radiation performance [half-power beamwidth (HPBW), SLL] has been experimentally obtained over a wide angular range ([−31.5°, 31.5°]), including low scanning loss and high radiation stability over the entire frequency range. High radiation efficiencies are demonstrated with this fully metallic design, particularly suitable for space applications. The mechanical simplicity offered by the concept is also quite attractive for low-cost multi-beam platforms.

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Shaped Continuous Parallel Plate Delay Lens With Enhanced Scanning Performance

This paper presents the design and measurement results of a 16-way radial power divider/combiner for solid state power amplifiers in the K band using an original assembly technique of the combined ways. The design is based on a radial non-resonant cavity connected to 8 peripheral rectangular waveguides with two waveguide-to-microstrip transitions inserted in each peripheral rectangular waveguide. Each combined way includes on the same tray the input and output waveguide-to-microstrip transitions and the MMIC amplifier location. The trays can be individually tested before mounting in the 16-way divider/combiner. The low insertion loss of the 16-way power divider/combiner leads to an estimated combining efficiency better than 86.5% from 16.5 GHz to 21 GHz with a maximum value about 88% from 17.2 to 19.2 GHz.

16-Way Radial Divider/Combiner for Solid State Power Amplifiers in the K Band

A novel quasi-optical beamformer based on a continuous delay lens was designed, manufactured and tested. The wide band and wide scanning capability is demonstrated at Ku band, as well as low return loss at all input ports and low mutual coupling. The agreement between measurements and simulations is outstanding, for both the S parameters and the radiation patterns.

Multiple beam antenna based on a parallel plate waveguide continuous delay lens beamformer

A novel compact and highly efficient dual-polarized horn-like antenna is presented. It exploits a radiating aperture that is fed by four smaller waveguides via a quad-furcated junction. The antenna also comprises the full feed network for the feed waveguides including an integrated 4-way orthomode power divider. Design principles are described in detail and illustrated by means of an example involving an antenna with aperture size of 2.6<inline-formula> <tex-math notation="LaTeX">$\lambda _{0} \times 2.6\lambda _{0}$ </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> the wavelength at the central frequency of operation) intended primarily for Geostationary Orbit (GEO) satellites. The antenna feed was designed to comply with the Additive Manufacturing rules and exhibits aperture efficiency levels close to the theoretical maximum ones over the entire transmit Ku band (10.7 – 12.75 GHz), while at the same time its profile is highly compact (6.4<inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula>). The measured results of a prototype 3D-printed in Selective Laser Melting (SLM) verified experimentally the calculated high aperture efficiency (over 90%). The total antenna feed attains return loss > 19 dB and maximum cross-polarization isolation (XPI) > 24 dB over a bandwidth of 18%. In light of the favorable electrical performances and compact size, the proposed solution constitutes an appealing alternative to profiled (or spline) horns for satellite antenna systems used either as reflector feeds or direct radiating arrays.

Quad-Furcated Profiled Horn: The Next Generation Highly Efficient GEO Antenna in Additive Manufacturing

A two-dimensional bifocal constrained lens design is introduced. This is found to be a good starting point for the design of continuous parallel plate waveguide beamformers. The proposed solution has the advantage to provide better scanning performance than the standard pillbox antenna, yet avoiding the complexity of alternative constrained lenses designs. Numerical results are provided to compare the proposed design with existing solutions.

Continuous parallel plate waveguide beamformer based on a bifocal constrained lens design

This paper presents two waveguide power dividers in a planar 4-way equiphasic dual-polarization power division configuration operating in the transmit Ku-band (10.7-12.75 GHz). Both concepts are primarily targeted as excitation networks for multiple accesses radiating elements or antenna arrays. The presented solutions are characterized by two different variants that accommodate for different manufacturing processes, namely subtractive manufacturing (SM) and additive manufacturing (AM). Their principal operations are described and finally their RF performance is presented and compared experimentally inter alia. The principal objective is to demonstrate the mechanical complexity of this type of microwave components and how 3D-printing enables its efficient realization via co-design.

Jean-Philippe Fraysse

Papers

16-Way Radial Divider/Combiner for Solid State Power Amplifiers in the K Band

Multiple beam antenna based on a parallel plate waveguide continuous delay lens beamformer

Quad-Furcated Profiled Horn: The Next Generation Highly Efficient GEO Antenna in Additive Manufacturing

Continuous parallel plate waveguide beamformer based on a bifocal constrained lens design

Four-Way Orthomode Waveguide Power Dividers: Subtractive and Additive Manufacturing