Marco A. Antoniades

A reconfigurable intelligent surface (RIS) is composed of low-cost elements that manipulate the propagation environment from a transmitter by applying phase shifts to incoming signals before they are reflected. This paper explores a unipolarized RIS with linear shape aimed at transmitting a common signal to multiple user equipments (UEs) spread across a wide angular region. To achieve uniform coverage, the uni-polarized RIS is designed to emit a broad and spectrally-efficient beam featuring a spatially flat-like array factor, diverging from the conventional narrow beam approach. To achieve this objective, we start by deriving probabilistic lower and upper bounds for the average spectral efficiency (SE) delivered to the UEs. Leveraging the insights from the lower bound, we focus on optimizing the minimum value of the power domain array factor (PDAF) across a range of azimuth angles from −π/2 to π/2 . We employ the continuous genetic algorithm (CGA) for this optimization task, aiming to improve the SE delivered to the UEs while also creating a wide beam. Extensive simulation experiments are carried out to assess the performance of the proposed code, focusing on key metrics such as the minimum and average values of the PDAF and the SE delivered to the UEs. Our findings demonstrate that the proposed code enhances the minimum SE delivered to the UEs while maintaining the desired attribute of a broad beam. This performance is notably superior to that of established codes, including the Barker, Frank, Golay, and Chu codes. Moreover, the effectiveness of the proposed code in generating a broad beam is experimentally validated using a RIS prototype.

This work presents a programmable metasurface framework featuring a modular, tile-based architecture that decouples the control electronics from the metasurface panel. Unlike traditional monolithic designs that have challenges in terms of scalability and ease of deployment, the proposed framework targets physical scalability, with tiles interconnected via a serial communication protocol. Intra-tile control is achieved using a microcontroller, and sixteen 4-channel digital-to-analog converters per tile, providing independent biasing for each unit-cell. A graphical user interface allows configuration of the connected tiles, assignment of biasing voltages, and control of the wavefront shaping functions. The prototype demonstrator operates with metasurface panels designed for C-band, with measured beam steering of around -45° to +45° phase shift range, approximately 15 dB gain, power consumption of 2.55 W/tile and a reconfiguration delay of about 231.5 ms. With its compact thickness, scalable reconfiguration, and potential compatibility with multiple metasurface designs, the proposed framework provides a practical and versatile foundation for a wide range of applications in programmable metasurface and intelligent surface systems.

The theory, design and experimental validation of a circularly polarised (CP) metamaterial fixed‐beam leaky‐wave antenna (LWA) with zero beam‐squinting (ZBS) is presented in this paper. It consists of two oppositely directed negative‐refractive‐index transmission‐line (NRI‐TL) LWAs, which are fed through an NRI‐TL 180 balun. Each NRI‐TL LWA generates its own beam and when the two beams, which radiate is opposite directions, are combined, they produce a fixed‐beam over a wide zero beam‐squinting bandwidth. This NRI‐TL 180 balun is specifically implemented to achieve CP radiation with enhanced gain at the broadside direction. Therefore, a detailed analysis of the NRI‐TL 180 balun is presented. Finally, the measurement results of a realised broadside circularly polarised fixed‐beam LWA are presented and discussed. It is shown that the addition of the NRI‐TL balun doubles the gain of the metamaterial LWA, since both orthogonal components, both co‐ and cross‐polarisations are utilised providing CP and enhanced radiation gain and efficiency. The antenna's beam‐squinting bandwidth is approximately 0.9 GHz, accompanied by an axial ratio of around 1.3 and exhibits an average radiation efficiency of 80.

This work conceptualizes wireless power transfer (WPT) between a tracking stationary ground transmitter and a mobile aircraft. Initial ground tests are performed to determine the viability of the Friis equation, using rectennas developed for operation at 2.45 GHz at 4 dBm of optimal input power. An achieved rectifier operation efficiency of 59% is reached at this power level. A model for analyzing received power during WPT tests in flight conditions is then developed and applied for various flight paths possible with a small, electric UAV, using the designed rectenna for power conversion on the aircraft. A maximum of 429 mW is received when the aircraft is flown in a circular path centered around the ground transmitter, with a radiated power of 7 kW. Various other loiters are also analyzed, including racetrack, elliptical, and infinity‐shaped loiters. The racetrack and elliptical loiters performed similarly with an approximate transmitted power of 4.5 kW and received power of 300 mW. The infinity loiter performed the worst with only 150 mW of received power with nearly 8.2 kW transmitted, which occurred primarily due to polarization mismatch between the transmitter and rectenna.

Presented is the analysis and design of a leaky-wave antenna (LWA) that radiates an off-broadside beam with zero beam-squinting (ZBS), operating at a frequency of 5.5 GHz. A general design methodology is presented, which can be used to design any fixed-beam leaky-wave antenna with different design requirements. Two oppositely-directed branches of LWAs utilizing negative-refractive-index transmission-line (NRI-TL) metamaterials are employed in the design. To achieve off-broadside radiation with zero beam-squinting, it is necessary for one branch to operate within the left-handed region, while the other branch to operate within the right-handed region. A 50-ohm microstrip line is used to feed the two NRI-TL LWAs which radiate two appositively directed beams whose combination results in a wideband off-broadside beam. The antenna was validated experimentally, and its fixed-beam operation was achieved for approximately a 20% fractional bandwidth.

An optically reconfigurable metasurface antenna for Future G beam steering applications is demonstrated experimentally. Optical reconfigurability is achieved by using photodiode arrays to provide a photovoltage to varactors, which in turn provide the required phase shift to enable beam-steering. Illumination of the photodiodes is provided over free space by using a galvo scanner to deflect a laser beam which is delivered from a high-power laser via a multicore fiber. In addition to delivering power over fiber, the same multicore fiber is also used to deliver a 64-QAM 5G NR signal to the metasurface antenna unit. Measured EVM values ranging from 3% to 5.7% for a beam-steering range of 58° are obtained. The use of a galvo scanner for free space illumination of the metasurface antenna not only eliminates the requirement for on-antenna DC bias networks (thus reducing the system complexity), but also allows greater control over illumination of the photodiode arrays, resulting in continuous beam-steering over 58°.

A synthesis procedure for designing linear Fabry–Perot (FP) leaky-wave antennas (LWAs) fed with nonuniformly-spaced subarrays is presented. First, the array-fed FP LWA is modeled by the superposition of the excited leaky waves that includes the mutual coupling effects. To that end, the dominant leaky mode and the dispersion curves are calculated using the finite element analysis of the eigenmode problem without any homogenization approximations. A procedure is proposed to numerically calculate the self-coupling and mutual-coupling coefficients for the excited leaky waves and include them in the model. Finally, a hybrid method based on convex ℓ ₁ -norm minimization and particle swarm optimization is applied to the model to group the source array elements into a minimum number of subarrays, while fulfilling the predefined mask-type radiation and element location constraints. Two linear FP LWAs are synthesized at 10GHz to demonstrate the effectiveness of the model and the optimization tool in designing highly-directive antennas with controlled sidelobe levels; the first achieves a half power beamwidth (HPBW) of 0.95°, aperture efficiency of 83.4%, and sidelobe level (SLL) of -19.5 dB using three subarrays, while the second achieves a HPBW of 1.05°, aperture efficiency of 82.9%, and SLL of -29.3 dB using nine subarrays.

A multifunctional and reconfigurable programmable metasurface (PMSF) is presented in this work that is enabled by an application-specific integrated circuit (ASIC). The enabling ASIC integrates control, digital-to-analog converters and loading elements to programmatically alter the response of the PMSF unit cells, while minimizing power consumption and cost. These programmable unit cells subsequently comprise a larger PMSF, which provides control of the reflected magnitude and phase for a given incident wave for both transverse electric (TE) and transverse magnetic (TM) polarizations. With this ability, the reflected wave can be set to zero, and both polarizations can be perfectly absorbed simultaneously and independently up to oblique angles of incidence of 60° for TE polarization, and 70° for TM polarization. The PMSF finds applications in smart wireless environments by providing the capability to redirect incident waves in a programmable manner, while also enabling the perfect absorption of incident interfering waves and programmatically synthesizing complex and polarization agile wavefronts. The accompanying paper, Part 2 focuses on the wavefront synthesis and performance while in this paper, the design and characterization are presented.