We propose a quasi-closed-form refractive index profile for flat radial gradient index (GRIN) lenses that allows the generation of direction-steerable quasi-nondiffracting beams in a wide frequency range. The GRIN profile is derived so that the optical path lengths of rays reaching the lens aperture are linearly correlated, leading to the generation of quasi-nondiffracting beams within a rhombic region near the lens. Detailed phase error analysis demonstrates that the proposed formulation is valid for a wide range of GRIN lens parameters, including the maximum refractive index, the specified maximum edge phase (which determines the nondiffracting range of the lens), the focal distance, and the thickness of the lens. The validation of the proposed GRIN profile is tested by both full-wave simulations and measurements of a 3-D printed prototype. Experimental results reveal that the designed GRIN lens generates a 2-D scanning quasi-nondiffracting beam with a scanning range of +/- 25.6 degrees in elevation angle and full azimuth coverage from 26 to 40 GHz, spanning the entire K-a-band.

This study proposes a scattering-based approach to investigate soil moisture (SM) estimation over anisotropic bare soil using multistatic radar observations. Two data generation strategies are considered: polarimetric diversity, which uses both co-and crosspolarized measurements at L-band, and frequency diversity, which exploits L-and C-band copolarized measurements. A novel approach consisting of two steps is proposed: 1) numerical prediction of the normalized radar cross section using first-and second-order small-slope approximation (SSA) solutions of the scattering, adopting an anisotropic description of the soil surface and 2) application of a normalized CRLB to benchmark multistatic radar configurations through the worst case performance analysis across all tillage orientations. The investigation demonstrates that both data generation strategies offer remarkable performance (normalized CRLB index <0.2) in optimized multistatic configurations, with receivers positioned at large baselines (i.e., 100-400 km) relative to the main monostatic synthetic aperture radar (SAR). This geometric diversity enables robust parameter de-coupling that significantly outperforms conventional monostatic approaches. A bootstrap analysis reveals that over 80% of achievable multistatic geometries demonstrate excellent estimation performance, with improvement factors (IFs) exceeding 60 times relative to monostatic configurations. These findings provide quantitative information for next-generation bistatic SAR missions.

All-metal corrugated antennas offer compact and low-profile solutions well suited for space and aeronautic applications. In this work, a leaky-wave approach is employed to design and optimize such structures for improved broadside radiation performance. The modal dispersive behavior of a symmetric unit cell featuring complex-shaped corrugations, is analyzed using an in-house Method-of-Moments solver. Based on the dispersion, the broadside radiation of the corresponding radially periodic leaky-wave antenna is predicted and enhanced. Leaky-wavebased optimization techniques, namely open-stopband suppression and aperture-field tapering, are implemented to improve the gain/bandwidth trade-off for broadside radiation. An optimum corrugated tapered antenna is designed, which achieve a peak gain of about 29 dBi and a −3-dB broadside gain fractional bandwidth exceeding 6%.

This work proposes a new 4-port dielectric-based leaky-wave antenna engineered for integration with solar panels. It operates within the K-band frequency range from about 19.5 to 22 GHz. The antenna features an agile feeding system capable of supporting single-port, dual-differential, and circular polarization operating states, thereby significantly enhancing its flexibility. Building upon prior designs, the antenna employs a substrate integrated waveguide feed structure, replacing the conventional partial reflective surface with a high dielectric constant material, suitable for solar panel integration. While optimized for operation at 20 GHz - chosen for satellite communication applications - it can be reconfigured to operate effectively at other frequencies. Moreover, the design offers a highly directive radiation pattern, effectively combining efficient antenna performance with solar power harvesting capabilities. Notably, the antenna achieves an efficiency of approximately 80%.

All-metal corrugated leaky-wave antennas lend themselves to the realization of efficient and low-profile radiating devices thanks to their low material losses, compactness, and robust structure. This work investigates the far-field and nearfield radiation characteristics of annular, radially periodic corrugated configurations, designed based on a dispersive analysis of the leaky-wave mode supported by the corresponding linear structure, which allows optimization of broadside gain and bandwidth. We propose the study and design of an optimized leaky-wave launcher to significantly improve both near- and far-field radiation performance. Two different original feeders incorporating a metallic covering structure are introduced, they effectively suppress direct feed radiation. The reported numerical analyses confirm enhanced, high-gain, and wideband broadside radiation, and demonstrate the possibility of generating a nondiffracting beam, implemented here in the form of a zeroth-order Bessel beam. This opens new and promising opportunities for generating focused beams using compact and efficient devices at millimeter-wave frequencies and beyond.

Corrugated metal surfaces are practical structures for the realization of a wide range of guiding and radiating devices thanks to their ease of fabrication, compact dimensions, and frequency-dispersion properties. Here, we present an original dispersive study of a parallel-plate waveguide with corrugated bottom plate radiating through slits on its top plate. A modal dispersive analysis is carried out using a method-of-moments approach, which allows for the investigation of both proper and improper leaky-wave regimes across the bandwidth where a single leaky wave is present. The leaky modal solution is studied, showing different behaviours around the broadside radiation frequency according to the geometrical parameters of the structure. By including two asymmetric slots in the same period at a suitably optimized distance, the stopband is suppressed and continuous scanning from backward to forward directions can be achieved.

This paper presents an overview of RadioMetOP, a weather-aware link-budget optimization chain designed to maximize received data while minimizing losses in satellite communications, particularly at frequencies above the classical X band. Unlike traditional approaches based on fixed climatological statistics, which tend to be overly conservative in the Ka band, RadioMetOP uses numerical weather prediction (NWP) and radiative transfer modeling to forecast atmospheric channel conditions, enabling dynamic adaptation of downlink parameters. Originally developed for the ESA BepiColombo mission to Mercury, RadioMetOP integrates three sequential modules: NWP, radio-propagation modeling, and link-budget modeling. After a feasibility phase (2013-2016) and validation with JAXA Hayabusa-2 mission (2019-2020), the system was operated in support of BepiColombo from 2021 to 2024. Across these phases, RadioMetOP achieved annual data-volume gains of 20-30% over classical techniques, with negligible losses and forecast accuracies above 98% for key propagation parameters. These results demonstrate its maturity for operational deployment in deep-space missions, as well as its applicability to non-geostationary satellite systems, where rapidly varying geometry and atmospheric conditions require accurate and high-resolution propagation forecasts.

The modulation of the attenuation constant in a periodic leaky-wave antenna (LWA) with open stopband (OSB) suppression is explored in this work. By properly adjusting the profile of the attenuation constant along the LWA aperture, the aperture efficiency can be improved, increasing the directivity. A bi-directional grounded dielectric slab with periodic metallic strips is used to demonstrate the possibility to taper the attenuation constant while mitigating the OSB. As demonstrated, the maximum directivity at broadside is improved from 12.57 dB to 12.92 dB by only modifying the dimensions of the unit cells. Moreover, the broadside bandwidth is also improved from 0.78 GHz to 0.92 GHz. Further optimization procedures are progress and the results will be reported at the conference.

Periodic leaky-wave antennas can be realized with planar low-profile structures supporting the generation of highly directional beams with frequency scanning from backward to forward directions. We propose a method to generate leaky modes with continuous scanning with an all-metal periodic 2-D (i.e., invariant along a direction normal to the propagation) waveguide. Periodic corrugations are introduced to support a slow wave, which is transformed with periodic slots etched on the top plate into a fast radiating waves. Suitable choices of the corrugation and the slot periods lead to a single fast backward-forward spatial harmonic being responsible for well-defined and directional radiation. This new method is demonstrated here proposing an original unit cell, properly optimized to suppress the open stop band. The analysis and the design is accomplished with a rigorous in house periodic method-of-moment code, allowing for the computation of complex modes in open 2-D waveguides. The leaky-wave antenna is studied and validated by means of full-wave simulations in Ka band. The structure features continuous beam scanning with broadside radiation at 29.7 GHz with beam scanning, realized gain, and efficiency comparable to different antenna technologies having thickness ten times larger.

This article presents the study and design of periodically corrugated all-metal structures, a class of compact, low-profile antennas suited for space and aeronautic applications. Leaky-wave theory is employed to guide their design and optimization. A method-of-moments (MoM) solver is used to characterize the dispersion of different unit cells (UCs), providing new insights into their modal behavior. By studying the dispersion, the radiation performance is predicted and significantly improved with respect to the state of the art. Highly directional, compact, and robust 2-D radially periodic leaky-wave antennas (LWAs) are proposed and validated through full-wave simulations. Broadside gain-bandwidth tradeoff is improved by suppressing the open stopbands (OSBs) of the original UCs via geometric asymmetries and, for the first time, by jointly tapering the phase and attenuation constants of the leaky mode. Using a figure of merit, all proposed antennas are shown to significantly outperform the state of the art for all-metal 2-D corrugated antennas, clearly demonstrating the advantages of the leaky-wave approach.

This paper introduces a double-strip bull's-eye (BE) antenna design, featuring the addition of a central disc and with substrate-integrated waveguide (SIW) feeding. These attributes make the design particularly suitable for near-field applications, and were the generation of adaptable Bessel beams is of interest. More specifically, the proposed design and feeding configuration facilitates the generation of both zeroth- and first-order Bessel beams as required; i.e. by applying differential phase excitation (0 degrees, 180 degrees) or common phase excitation (0 degrees, 0 degrees) to the external ports, the antenna can demonstrate versatile beamforming functionality. Also, the design has the capability to extend the non-diffracting range (NDR) as well as the operational bandwidth of the antenna launcher when compared to similar implementations as reported in the literature, thereby enhancing its practicality for near-field applications. In particular, the antenna launcher offers a promising solution for advanced near-field communications, sensing scenarios, and new wireless power transmission systems.

This work investigates the generation of Bessel beams from a double-strip bull-eye planar leaky-wave launcher. The structure offers wideband operation and an extended non-diffracting range, thanks to the suppression of the open stopband, which typically affects periodic leaky-wave antennas. A comparative analysis is reported with a single-strip implementation, which shows the stopband and therefore offers a reduced non-diffracting range. To enhance functionality with respect to conventional bull-eye structures operating in the near-field, the double-strip launcher is excited through a flexible substrate integrated waveguide multiport feeder, which enables dual-polarization and controllable aperture fields and allows for the generation of both zeroth- and first-order Bessel beams. Both simulations and measurements are reported, demonstrating beam focusing over larger distances in the near-field. Also, for the first time, an adaptable and polarization agile launcher is studied and experimentally validated to increase the non-diffractive range of a planar and compact structure.

Corrugated metal planar surfaces enable the realization of a wide range of guiding and radiating devices due to their compact and robust structure. Due to their negligible material losses, these all-metal configurations are ideal candidates for space and aeronautic applications. We present here the dispersive analysis of an all-metal plane featuring complex-shaped corrugations. By means of an in-house method of moments, a dispersive analysis of the corresponding unit cell is performed. The results are compared with full-wave simulations achieved by implementing a full-wave Bloch analysis of the unit cell. Within the same frequency range, both the top and the bottom sides of this structure are analyzed and the corresponding transverse magnetic leaky mode (with respect to the direction of propagation) are presented. Each side of the metallic plane thus supports the design of an all-metal planar antenna, whose maximum broadside directivity can be optimized by properly tailoring the corresponding dispersion.

The analysis and processing of satellite remote sensing data have established new paradigms to observe the Earth and to study climate changes. Data collected by sensors and systems operating across the entire frequency spectrum carry on enormous information content. They enable systematic retrieval and characterization of biogeophysical variables. The retrieval of these variables, however, is often hindered by limitations, such as missing data, low spatial and temporal resolutions, and insufficient co-located ancillary data. These challenges arise due to factors, such as sensor limitations, dead pixels, cloud cover, and discontinuous data acquisition. To overcome these issues, numerous techniques have been proposed, ranging from classical interpolation methods and spectral transforms to modern artificial intelligence-based approaches. This article presents a comprehensive and critical review of satellite remote-sensing data augmentation methods, focusing on how interpolation theory and artificial intelligence techniques can be effectively applied to reconstruct missing data and enhance the quality of retrieved biogeophysical variables. This roadmap offers a comprehensive framework that categorizes and evaluates existing methods, highlights their strengths and limitations, and identifies promising areas for future exploration.

Corrugated metal planar surfaces lend themselves to the realization of a wide range of guiding and radiating devices thanks to their compact and robust shape. In a homogenization regime corrugated metal surfaces can support a proper surface-wave mode. At higher frequencies, i.e., when the unit cell period and the free-space wavelength are comparable, they support proper and improper leaky-wave regimes. Here, we present an original dispersive study of a corrugated all- metal plane constituted by narrow grooves. A modal dispersive analysis is carried out using a method-of-moments approach. We investigate the proper and improper surface-wave regime across a relatively large spectrum. An interesting modal solution is achieved, showing large variations of the attenuation constant, an open stop band at the forward/backward transition and higher frequencies stop bands. A large region just after the open stop band is achieved where the phase constant is smaller than the attenuation constant, potentially offering wideband broadside radiation. The structure can support the design of an all-metal planar antenna.

We demonstrate the application of a 2-D Bull's-Eye (BE) leaky-wave antenna (LWA) for conical direction finding using the frequency scanning mechanism. In contrast to other 2-D LWAs of uniform or quasi-uniform nature, such as Fabry-Perot Antennas (FPAs), the BE-LWA has a periodic nature and therefore its radiation mechanism is based on a higher-order space harmonic. As a result, both the backward-scanning and forward-scanning bands can be used to increase the direction finding performance. This is demonstrated with theoretical results using a printed-circuit BE LWA operating in the frequency band from 14 GHz to 32 GHz.

A radially periodic 2-D leaky wave antenna (LWA) with high gain at broadside, reduced sidelobes, and suppressed open-stopband (OSB) is presented in this communication. The antenna is low profile and is defined by a printed, double microstrip bull's-eye aperture. To support polarization and pattern agility, as well as applications in full-duplex systems and dual-polarization scenarios, the antenna is fed with a compact multislot array at the center of LWA, enabled by substrate integrated waveguide (SIW) technology. When considering differential excitation, the simulations and measurements demonstrate a maximum realized gain of more than 17 dBi at broadside at about 18.4 GHz. Furthermore, due to the suppression of the OSB, persistent broadside radiation is supported from 18 to 19 GHz, along with continuous and sustained directive radiation when the main beam scans through broadside, which is in agreement with leaky-wave (LW) theory. Applications include vehicle antennas and V2X communication systems, satellite connectivity, polarization and pattern diversity scenarios, radar and monopulse systems, as well as 5G/6G wireless communications.

We study a 2-D leaky-wave antenna (LWA) with suppressed open stopband (OSB) operating both in the near- and far-field, offering enhanced performance compared to existing designs. In particular, two configurations, a double strip (DS) and a single strip (SS) bull's-eye (BE) LWA structure, are analyzed and compared. The DS launcher demonstrates superior broad-band performance, maintaining efficient beam collimation across a wide frequency range in the near-field and enabling continuous beam scanning in the far-field as a function of frequency. In contrast, the SS configuration exhibits an open stopband at about 19.2 GHz and without continuous radiation. Both launchers employ a coaxial TM-polarized feed mechanism to ensure optimal power transfer, and dispersion curves show identical crossover frequencies for both BE antenna implementations. However, the suppression of the OSB combined with the wide band capability of the DS configuration, highlights the potential of this design for next-generation high-frequency communications, wireless power transfer, and, radar systems operating in the near- or far-field.

In this work, we study the impact of the reactive phenomena on the efficiency of uniform leaky-wave antennas radiating at broadside. First, we present analytical expressions to evaluate the different terms of the attenuation constant of the leaky mode, i.e. the active attenuation constant, related to radiation and material losses, and the reactive attenuation constant, related to energy stored in the fields. Secondly, the impact of the reactive attenuation constant on the efficiency of leaky-wave antennas is studied, showing that a maximum radiation efficiency of $\eta_{\mathbf{r a d}}=70.7 \%$ is obtained at the splitting point where the phase constant and the attenuation constant of the leaky mode equalize ($\beta_{z}=\alpha_{z}$). Finally, optimum conditions to maximize the gain when radiating at broadside are derived, finding that a ratio of $R=\beta_{z} / \alpha_{z} \approx 1.6$ provides the best tradeoff between radiation efficiency and aperture efficiency.