Antonio-Daniele Capobianco

The growing demand for higher capacity in wireless communication networks has created a critical need for smart devices with dynamic focusing and beam steering capabilities in the 5G mid-band spectrum. Conventional focusing techniques and metasurface-based flat lenses often suffer from static operation and mechanical complexity, restricting their practical use in adaptive platforms. In this work, we propose a reconfigurable reflective lens based on plasma-filled glass tubes designed to operate at 5 GHz. Through full-wave numerical simulations, we demonstrate that selective modulation of plasma density permits continuous focal length tuning from 1.5λ to 3.5λ. Furthermore, by increasing the number of plasma tubes, we achieve dynamic lateral shifts of the focal spot exceeding 2λ. Compared with prior reconfigurable lens approaches in the microwave and millimeter-wave range, the proposed design offers a broader tuning range and introduces lateral reconfigurability, which has not been previously reported. These results highlight the potential of plasma-based flat lenses as a compact, fast, and energy-efficient solution for integration into next-generation wireless communication systems.

This article reviews the use of plasma, liquid metal, and liquid crystal technologies in the development of reconfigurable antenna systems. These approaches offer promising alternatives to conventional reconfiguration methods based on semiconductors and Micro-Electro-Mechanical Systems (MEMS). A common feature among plasma, liquid metal, and liquid crystal implementations is their ability to manipulate electromagnetic radiation through dynamic changes in material properties. Plasma technology enables a transition between dielectric and conductive states, allowing for versatile control of antenna behavior. Liquid metals facilitate the reconfiguration of metallized regions within antenna structures, while liquid crystals provide continuous tunability of dielectric permittivity. This review explores various application scenarios where these technologies are employed, both in antenna systems and in associated circuitry. Key performance indicators are defined for each technology to facilitate quantitative comparisons among them and against traditional semiconductor and MEMS-based solutions. This comparative analysis highlights potential synergies among the three technologies, as well as their respective advantages and limitations. Finally, the article outlines the critical steps required for each technology to overcome current challenges and progress toward commercialization.

A multilayer log‐periodic metasurface patch antenna (LPMPA) operating in the 4–9‐GHz frequency range with broadside radiation is presented. This antenna array is characterized by its compact size and low profile. Each element of the LPMPA consists of a 2‐D periodic structure of 4 × 4 square patches, which can be viewed as a metasurface. The array is excited through aperture coupling in the ground plane beneath the radiators. The proper phase progression of the currents for a broadside radiation of the LPMPA′s elements in the active region is obtained by increasing the length of the feed line placed between adjacent radiators. The structure′s stop‐band caused by the excess of length between radiators is eliminated by increasing the characteristic impedance of the feed line to 70 Ω in the proximity of each slot. A prototype of the proposed antenna, consisting of four 2‐D periodic structures, is fabricated and tested. The obtained results show a 76% fractional bandwidth with gain ranges between 8 and 13 dB.

This work introduces a metalens designed to focus electromagnetic power in a magnetized plasma, primarily applied in electrodeless space propulsion. The focusing capability relies on the misalignment between the wavevector and the Poynting vector in a magnetized plasma. The metalens is synthesized initially by approximating it as a sheet with an equivalent tensorial susceptibility. Its constituent elements are then engineered to achieve the desired theoretical behavior. Numerical simulations confirm the effectiveness of the proposed design. The key novelty of this work lies in developing a metalens specifically tailored to focus electromagnetic power in a magnetized plasma, an anisotropic medium, rather than in free space.

This paper analyses electromagnetic (EM) wave propagation within a metasurface-cladded waveguide filled with magnetized plasma. First, an analytical model is developed to understand the governing dynamics of the system. Second, a realistic numerical design is presented to assess the feasibility of the proposed concept. This technology targets microwave-driven plasma production, with the cladding metasurface enabling control over the cut-off frequency of the waveguide. Results suggest that EM propagation can be triggered regardless of the value of the static magnetic induction field. This represents a significant advance over standard implementations, promoting system miniaturization and facilitating the integration of waveguides with plasma sources.

A architecture of reconfigurable analog computing devices is proposed for image processing and advanced wireless communication systems, such as those required for self-driving cars. This architecture is designed to work in the terahertz frequency range, and it is based on a metasurface made of VO ₂ brick resonators as metaatoms. The system is capable of performing first-order and second-order derivative, or it may act as a mirror for impinging signals in a broad range of terahertz frequencies. The reconfigurability between these functions is achieved by tuning the temperature of the VO ₂ resonators, which can be switched between the metallic and the insulator state with an electric current passed through a back metal layer. Following this approach, we present two dynamically controlled metasurfaces, one designed in k-space and the other in real-space.

This work proposes a metasurface-cladded waveguide which may be filled with positive- or negative-epsilon materials. This design targets microwave plasma technology, particularly devices intended to be loaded with tenuous and dense plasma. Namely, the dielectric permittivity of the filling material is positive or negative, depending on the scenario. First, a theoretical model has been proposed to assess the electromagnetic propagation regime. Specifically, the cladding metasurface is treated as an anisotropic surface impedance imposed at the edge of the waveguide. Second, a possible design relying on a hollow dielectric substrate whose internal surface is coated with a lattice of metallic patches is numerically investigated. The results show that the waveguide propagates electromagnetic waves independently from the sign of the dielectric permittivity of the filling material. The latter parameter and the geometry of the metallic lattice are shown to be governing design parameters, in particular, in determining the cut-off frequency of the fundamental mode.

This paper aims to comprehensively review the literature on Gaseous Plasma Antennas (GPAs). These innovative devices transmit electromagnetic (EM) signals through ionized gas, known as plasma, instead of conventional metal structures. GPAs offer distinct advantages over their metallic counter-parts, particularly in performance reconfigurability. The paper begins by evaluating the EM properties of the plasma medium, exploring methodologies for its generation, measurement, and simulation. Subsequently, the prevalent GPA architectures are presented, distinguishing between active and passive concepts based on the plasma’s primary role: either emitting EM signals or manipulating them. Additionally, unconventional GPA implementations, such as explosive or laser-based technologies, are examined. Finally, the paper assesses the most promising applications for leveraging GPAs in various fields.

This work presents the theoretical and numerical design of a cylindrical waveguide that supports Spoof Surface Plasmon Polaritons (SSPP) at microwave frequencies. First, a theoretical model is proposed to assess the propagation of SSPPs in a cylindrical geometry and to estimate the surface impedance required to enable these wave modes. The reliability of the theoretical model is verified against numerical results. The proposed cylindrical waveguide embeds a cladding metasurface with a dielectric substrate covered by a lattice of square metallic patches. According to numerical estimations, the proposed design allows the propagation of SSPPs in the frequency range 2.2–5.7 GHz. Notably, the cut-off frequency is lowered by approximately 3.5 GHz with respect to conventional metallic solutions. The target application of the proposed waveguide is efficient plasma generation.