An aperture-coupled reflectarray element giving a full phase tuning range with a single varactor diode is proposed in this paper for pattern reconfigurability applications. The full phase agility is achieved by a proper optimization of the phase tuning line, thus providing an alternate inductive/capacitive effect able to avoid the use of two varactor diodes, usually adopted in similar existing configurations. The proposed active element structure is adopted to design a demonstrative reflectarray prototype of 3 × 15 radiators. Furthermore, an own synthesis procedure is applied to obtain the proper biasing voltages giving the prescribed H-plane field. Test examples of beam-scanning, multibeam, and shaped-beam patterns are discussed to demonstrate the effectiveness of the approach.

A dual-band dual-linear polarization reflectarray configuration is developed for future 5G cellular applications. A single layer unit cell including two pairs of miniaturized fractal patches is designed to operate at two distinct frequencies within the Ka-band (27/32 GHz), in a dual-polarization mode. An in-depth analysis of the unit cell behavior is carried out, to demonstrate the total independence between the designed frequency bands and polarizations. The proposed configuration offers a very simply and thin structure, small unit cell sizes, and low losses, while leading to an independent optimization of the phase at each frequency and polarization. A dual-band/dual-polarized reflectarray prototype is designed and numerically tested, thus demonstrating the unit cell flexibility to offer arbitrary beam directions/shapes at each frequency, for both polarizations.

A novel fractal-based metamaterial unit cell, useful for ambient power harvesting, is proposed to operate within the 2.45 GHz Wi-Fi band. The simulated fractal cell offers very high absorption coefficients, a wide-angle and polarization-insensitive behavior, and very small size. A 9 × 9 fractal-based metamaterial harvester is designed and simulated, by demonstrating a very high harvesting efficiency equal to 96.5% at 2.45 GHz. The proposed metamaterial configuration could be very appealing for the implementation of high efficiencies and compact harvesting systems for wireless sensor network applications.

A Minkowski fractal geometry is proposed in this work as miniaturized absorber cell suitable for multipath phenomena mitigation within the European RFID UHF-band. The proposed structure is analyzed through the combined use of an equivalent transmission line model and MoM-based full-wave simulations. Very high miniaturization capabilities (about 50% with respect to standard configurations) are demonstrated for a 868MHz absorber unit cell, characterized by an absorptivity more than 99%, a good angular stability and a very thin substrate ($\lt \lambda_{0}/100$). The proposed configuration is appealing for designing compact absorbers useful for multipath reduction in wireless systems operating on restricted indoor environments.

This paper provides an overview of fractal antennas and metasurfaces, exploring their design principles, performance, and applications. Fractal antennas, incorporating self-similar geometric shapes, offer several advantages, such as their multiband operation, compact size, and improved performance. Metasurfaces, on the other hand, are two-dimensional structures composed of subwavelength unit cells and are designed to achieve advantageous and unusual electromagnetic properties by enabling precise control over electromagnetic waves. This paper discusses the fundamental concepts of fractal antennas and metasurfaces, compares their characteristics, and presents the latest advances in research. Additionally, it highlights applications in wireless communications, energy harvesting, sensing, and beyond.

We present a new approach to the problem of detecting element failures in any kind of array antenna. The proposed method requires only phaseless information on the generated field and reduces as much as possible the number of needed measurements by exploiting the Compressed Sensing (CS) theory. The solution procedure works regardless of whether the probes are located in the near-field or far-field region of the antenna under test, and it is the first and only CS-based technique able to perform the diagnostics by exploiting only phaseless measurements taken exclusively in the near-field zone. It also results simple and fast as it requires a single measurement surface and reduces, in most practical instances, to the solution of a convex programming problem. The given theory is supported by very many numerical experiments involving full-wave electromagnetic simulations of realistic arrays and considering both scalar and vector fields with different types of scanning surfaces and different noise levels. Both ON-OFF and phase faults are dealt with. An experimental validation on a fabricated array is also presented.