This work presents the design and experimental validation of a full-metal 1-bit mechanically reconfigurable intelligent surface operating in the 14–18 GHz band. It is made of 30×30 slot-ring unit cells arranged in a panel with one-dimensional control. Measurements confirm two reflection states with a 180$^\circ \pm \,20^\circ$ phase difference over a 19.7% relative bandwidth. The surface achieves beam steering up to $\pm$ 40$^\circ$ under normal incidence and operates under oblique incidence up to 30$^\circ$ in the E-plane.

This letter proposes the design and measurement of a periodic metasurface that achieves anomalous reflection with reduced RCS in a given parasitic direction. A previous study proposed a semianalytical model to predict the RCS behaviour of such a metasurface. However, this first study did not include any experimental exploration to verify the theoretical results. To complete this study, this work presents an experimental validation of the proposed design, with a focus on manufacturing and measurement issues. The synthesis, design specifications, fabrication method and experimental setup are presented and discussed. Measurement results are also examined in detail, highlighting some limitations in metasurface RCS measurements. The proposed metasurface effectively achieves the predicted RCS level reduction in the considered parasitic direction. The agreement between simulation and experimental results demonstrates the accuracy of the modelling and the efficiency of the optimisation procedure.

In future wireless communication systems, millimeter waves (mmWaves) will play an important role in meeting high data rates. However, due to their short wavelengths, these mmWaves present high propagation losses and are highly attenuated by blocking. In this chapter, we seek to increase the indoor radio coverage at 60 GHz in non line-of-sight (NLOS) environments. Firstly, a metallic passive reflector is used in an L-shaped corridor. Secondly, an array of grooved metallic antennas of size 20 cm x 20 cm (corresponding to 80 grooves) is used in a T-shaped corridor. Next, the study focuses on the blockage losses caused by the human body. The results obtained in these different configurations show that it is possible to use beamforming to exploit a reflected path when the direct path is blocked.

This article explains the nonidealities that arise when using p-i-n diodes at millimeter-wave frequencies and the important limitations that they bring in classical configurations of 1-bit slotline reconfigurable unit cells. A robust solution is proposed where a single p-i-n diode is inserted inside a ring topology. The slotline unit cell is analyzed through a circuit-model approach. Its performance is compared with a unit cell based on a single slotline, which also includes a p-i-n diode, referred to as classical configuration. For experimental assessment, a circuit prototype is fabricated to verify the phase difference of both p-i-n-diode states in each unit cell configuration. The measured results reveal that the slotline unit cell with ring configuration provides a 180(degrees) +/- 20(degrees) reflection phase difference from 36.3 to 45 GHz (21.4% relative bandwidth). Finally, the proposed slotline unit cell with ring topology is measured in a complete array to assess its performance in periodic and quasi-periodic environments. The measurements confirm the 1-bit behavior for both normal and oblique incidences with losses less than 2 dB. Therefore, this enables the design of wideband 1-bit reconfigurable reflectarrays and reconfigurable intelligent surface (RIS) in this frequency range.

1-bit coding metasurfaces, which combine two basic unit cells with out-of-phase responses, have shown significant potential for achieving diffuse scattering, making them valuable for radar signature control. This paper presents a simple metal-only unit cell to design metasurfaces for radar cross-section reduction. The various steps of designing this unit cell are outlined. The recently introduced Minimum Peak Sidelobes codes in the field of coding metasurfaces, associated with the metal-only unit cell, are being utilized to validate their diffusion capabilities through electromagnetic simulations. The results are compared to those obtained with an analytical approach. To enhance performance and align more closely with the analytical approach, modifications to the unit cell are presented, which involve adding rooftops.

This paper presents reconfigurable intelligent surface unit cells based on a loaded slot ring topology. The use of rings enables an increased bandwidth for PIN diode-based reconfigurable unit cells. Measurement results demonstrate that the unit cell provides two phase states separated by 180°±20° over a 21.4% relative bandwidth centered at 40 GHz. The concept is then applied to a mechanically reconfigurable structure capable of achieving two configuration states with a phase difference of 180°±20° across a 20.3% relative bandwidth centered at 16 GHz. Full-wave simulations confirm the unit cell’s ability to steer beams up to a 60° angle when integrated into a surface configuration. These results demonstrate the viability of the proposed architecture for broadband reconfigurable intelligent surface applications.

This paper proposes a dual-polarized slotline unit cell for designing reflective metasurface at millimeter waves. The unit cell consists of a three-dimensional (3-D) assembly of PCB layers. The metallic pattern of each PCB layer implements an orthogonal short-circuited slotlines whose length can be varied independently to control the phase in reflection of each incident polarization. The performance has been studied for normal and oblique incidences, showing high levels of co-polar and a linear phase between 37 GHz and 44 GHz. Using the proposed unit cell, a use case is presented where a reflective metasurface is needed to improve the coverage at various positions of an NLOS scenario. Two design options for the phase distribution in the metasurface are discussed. Through their radiation patterns, a comparison is performed. The advantages of using a metasurface with a broad-beam for coverage over a large bandwidth and for different angularly separated positions are demonstrated.

Abstract A 3D metal‐only waveguide‐based phoenix cell for reflectarray is presented. The proposed cell consists of two concentric square waveguides and a metallic block in the centre, which offers two operation modes. The first mode uses its cross section to tune reflection phase while the second mode varies the heights of two waveguides to manipulate reflection phase. The principle of the two different modes is analysed in detail. A metal‐only reflectarray antenna at 20 GHz is designed based on the first mode of the phoenix cell. It is fabricated using selective laser melting 3D printing technology. A good agreement between simulations and measurements is achieved. The measured gain at 19.75 GHz is 30.25 dBi with an aperture efficiency of 51.17% respectively. Also, the measured 1‐dB gain bandwidth is 15% (19–22 GHz). A dual band metal‐only reflectarray operating at 20 and 25 GHz is designed based on the second mode of the phoenix cell. The two metal‐only reflectarray antennas fully demonstrate the capabilities of the proposed 3D metal‐only phoenix cell.

A reflectarray unit cell design with sensing capability at millimeter-wave frequencies is presented in this paper. The proposed unit cell is based on slotlines spatially arranged in 3-D. There are different parts that conform the reflectarray unit cell, these are: an impedance transformer, a main slotline, an EBG filter and a sensing zone. By modifying the length of the main slotline, phase tuning of the reflected wave is achieved while preserving good level of reflection. Moreover, the phase response is linear in the frequency range that goes from 30 GHz to 50 GHz. To implement the sensing function, the EBG filter is placed after the main slotline to allow some level of leakage through the unit cell. The simulated results show that depending on the angular direction of an incident wave, there is a certain phase difference value among the sensors located in the sensing zone of the unit cell.

This letter proposes the design and measurement of a periodic metasurface that achieves anomalous reflection with reduced RCS in a given direction. A previous study proposed a semi-analytical model to predict the RCS behaviour of such a metasurface. This work focuses the discussion on manufacturing and measurement issues. The synthesis, design specifications, fabrication method and experimental setup are presented and discussed. Measurement results are also examined in detail, highlighting some limitations in metasurfaces RCS measurements. The proposed metasurface effectively achieves the predicted RCS level reduction in the Floquet direction considered. The agreement between simulation and experimental results demonstrates the accuracy of the modelling and the efficiency of the optimisation procedure.

One-bit coding metasurfaces combine two basic unit cells with out-of-phase responses. Their potential in achieving diffuse scattering has already been demonstrated. These metasurfaces can subsequently be applied to radar-signature control. This paper presents a theoretical analysis linking the scattered field to the autocorrelation of the code that encodes the metasurface. This analysis leads to a focus on Minimum Peak Sidelobes codes with autocorrelation characteristics similar to the unit impulse. Advances in other research areas have greatly enhanced the search for these kind of codes, making them directly usable for coding diffuse scattering metasurfaces. This approach is compared with existing codes, specifically examining how it performs against the optimal code found through exhaustive search in small-scale scenarios. Then, it is shown that this coding strategy facilitates the design of metasurfaces with any and large electrical sizes, achieving results comparable to those obtained through optimization-based approaches, at a significantly reduced computational workload.

A new antenna array architecture is proposed here to overcome a current bottleneck in phased arrays concerning the enhancement of radiation efficiency and avoidance of scan blindness. In contrast to the conventional approach of using patches with circular or square geometries that exploit 90 $$^\circ$$ or 180 $$^\circ$$ rotational symmetry, this work proposes to use waveguide radiating elements based on 120 $$^\circ$$ symmetry. To implement such symmetry, the tri-ridge aperture is proposed, and its capability to scan widely within a broad frequency bandwidth is demonstrated. A modal analysis is performed to explain the physical phenomena underlying such superior performance. A successful experimental validation is provided by means of a monolithic prototype built in metal additive manufacturing. The measured results show, for the first time, that it is possible to achieve high radiation efficiency and circular polarization when scanning widely in a broad bandwidth. Such an accomplishment constitutes a major achievement in the field of active electronically steered phased arrays, and impacts significantly the capabilities and potential of modern radar and communication systems.

This paper presents a dual-band metal-only antenna that operates at 20 and 40 GHz. The unit cell consists of a square waveguide with short circuit termination and a square metallic block in the center. Its performance is evaluated and analyzed in detail. The proposed metal-only antenna combines the functionalities of reflectarray and parabolic reflector antennas. At 20 GHz, the reflected beam is determined by a parabolic surface. At 40 GHz, the reflected beam is controlled by the phase distribution of cells in the antenna. The gain increases with frequency in the lower frequency band, which is similar to what happens in a parabolic reflector antenna. The antenna profile is significantly reduced and the antenna’s performance is improved after rotating the coordinate system. The antenna with reduced profile is fabricated using selective laser melting 3D printing technology. The measured results show that the proposed antenna can operate as parabolic reflector and reflectarray in the target two frequency bands.

Due to their periodic nature, metasurfaces used to perform anomalous reflection raise parasitic harmonic reflections. We show a classical synthesis example of such a structure and highlight its limitations. Floquet analysis and its associated simulation environment are exploited to understand the origin of these parasitic reflections and to mitigate them. The proposed method is based on the optimization of the metasurface periodic pattern: the supercell. A predictive method is built to calculate radar cross-section patterns from supercell Floquet simulation, avoiding dealing with heavy simulations. The proposed model, the optimization outputs, and the general results are exposed in details. Different cases are also discussed to prove the repeatability of the proposed method. An earlier version of this paper was presented at the European Microwave Conference and was published in its proceedings.

This paper presents a 3D metal-only waveguide-based phoenix cell. The proposed cell uses open-ended waveguides, which allow a portion of the incident wave to pass through the phoenix cell. It thus has the ability to control both reflection and transmission phases. Its principle is analyzed in detail. Two metal-only transmit-reflect-array antennas are then designed. The proposed transmit-reflect-array antennas are able to produce both transmitted and reflected beams at 16 GHz in the target directions simultaneously. One of the transmit-reflect-array antennas is fabricated using selective laser melting 3D printing technology. The measured results show that a good agreement between the simulated and measured radiation patterns is achieved. The side lobe and cross polarization levels at 16-GHz are −15.3-dB and −23.1-dB respectively. The measured gain of transmitted and reflected beams at 16-GHz are 25.7-dBi and 24.1-dBi respectively. Both the simulation and measurement results fully demonstrate the capabilities of the proposed 3D metal-only phoenix cell.

A metal-only reflect-transmit-array unit cell whose operation is dependent on the incident polarization is presented. The proposed unit cell is based on 3D geometry which allows a high level of independent phase tuning for orthogonal and linear incident polarizations. In our unit cell, the horizontal polarization is reflected while the vertical polarization is transmitted. The modification of the reflected phase is done by the length of a metal block located at the end of the slits where the horizontal polarization propagates. The modification of the transmitted phase is changed by the depth of the corrugations implemented in the slit that supports the propagation of the vertical polarization. The results obtained in transmission mode show an impedance matching below -15 dB with a linear phase response from 30 GHz to 50 GHz. For the reflected polarization, there is almost total reflection with phase performance that is also linear along the frequency.

This chapter intends to show the strong potential brought by metal 3D-printing to the field of waveguide components and antennas. General co-design guidelines are firstly provided. These guidelines enable to benefit from the advantages associated to metal 3D-printing. The implementation of filters and ortho-mode transducers is considered, together with horns and slotted antennas. Finally, multifunctional periodic structures benefiting from metal 3D-printing are discussed.

This paper presents a metal-only reflectarray that enables the control of incident orthogonal polarizations in a large bandwidth. The proposed reflectarray is based on a unit cell whose tuning elements allow the independent control of the reflection phase value for the vertical and horizontal impinging polarizations. Due to the symmetry of the unit cell, the same performance is produced by each polarization when its reflection phase response is modified. The proposed unit cell provides a fairly linear phase response along the frequency with a phase variation in the orthogonal polarization of ±1°. The performance under oblique incidence and the frequency limitation of the unit cell are also investigated. From this unit cell, a metal-only reflectarray that produces circular polarization from a linear polarization is designed. The reflectarray presents a simulated directivity greater than 27 dBi with an axial ratio below 1.5 dB from 32 GHz to 50 GHz (43.9% of bandwidth). A prototype is fabricated and the measured results agree well with the simulated ones. The obtained aperture efficiency is between 56% and 41% in the considered frequency band. The measured realized gain ranges from 27 dBi to 30.3 dBi where the achieved radiation efficiency is greater than 97%

This paper presents a dual band metal-only antenna that operates at 20/40GHz. The proposed metal-only antenna combines the functionalities of reflectarray and parabolic reflector antennas. The unit cell consists of a square waveguide with short circuit termination and a square metallic block in the center. At 20GHz, the reflected beam is determined by a parabolic surface. At 40GHz, the reflected beam is controlled by the phase distribution of cells in the antenna. The gain increases with frequency in the lower frequency band, which is similar to what happens in a parabolic reflector antenna. The aperture efficiency at 20/40GHz is about 22.99/43.79%.