Marco Righero

We describe an antenna measurement system that uses a cable-suspended system to move the probe antenna around the antenna to be characterized. Radio frequency data and pose data are acquired during the flight and processed later to derive the antenna radiation pattern. The post-processing leverages equivalent currents to deal with scattered data in an efficient way. We give details on the implementation of the measurement system and present results when reference antennas at 6 GHz and at around 1.25 GHz are measured, to show the system performance.

Objective: Microwave hyperthermia is a clinically validated adjunctive therapy in oncology, employing antenna applicators to selectively raise tumor tissue temperature to 40–44 °C. For deep-seated tumors, especially those in anatomically complex areas like the head and neck (H&N) region, phased array antennas are typically employed. Determining optimal antenna feeding coefficients is crucial to maximize the specific absorption rate (SAR) within the tumor and minimize hotspots in healthy tissues. Conventionally, this optimization relies on meta-heuristic global algorithms such as particle swarm optimization (PSO). Methods: In this study, we consider a deterministic alternative to PSO in microwave hyperthermia SAR-based optimization, which is based on the Alternating Projections Algorithm (APA). This method iteratively projects the electric field distribution onto a set of constraints to shape the power deposition within a predefined mask, enforcing SAR focusing within the tumor while actively suppressing deposition in healthy tissues. To address the challenge of selecting appropriate power levels, we introduce an adaptive power threshold search mechanism using a properly defined quality parameter, which quantifies the excess of deposited power in healthy tissues. Results: The proposed method is validated on both a simplified numerical testbed and a realistic anatomical phantom. Results demonstrate that the proposed method achieves heating quality comparable to PSO in terms of tumor targeting, while significantly improving hotspot suppression. Conclusions: The proposed APA framework offers a fast and effective deterministic alternative to meta-heuristic methods, enabling SAR-based optimization in microwave hyperthermia with improved tumor targeting and enhanced suppression of hotspots in healthy tissue.

Oncological microwave hyperthermia is a clinically proven sensitizer of radio- and chemo-therapies; it acts by selectively increasing the temperature of tumor cells by means of antenna applicators. Its current limitations mostly come from the inability to reliably predict, and hence control, temperature inside the patient during treatment, especially for deep-seated tumors. Simulations are employed in treatment planning, but due to related uncertainties invasive thermometry is necessary, usually via catheters. Being invasive, their use must be minimized and provides very limited spatial information. Here, we demonstrate an approach to obtain 3D temperature information in real time from few measurement points via massive use of high-performance simulations carried out prior to treatment. The proposed technique is tested both in a fully anthropomorphic in-silico scenario, and in an experimental controlled setting. The obtained results demonstrate the potential of the proposed method as a low-cost real-time temperature monitoring technique in cancer hyperthermia. Use with intra-luminal, minimally-invasive catheters is supported by the positive outcome experimentally obtained using data points directly acquired in the trachea-mimicking phantom structure.

Objective: Microwave hyperthermia is a clinically proven cancer treatment used in combination with conventional therapies to enhance the overall treatment outcome. It consists in selectively increasing the temperature of tumor cells to 40–44 °C by means of electromagnetic fields that are externally generated and coupled to the patient body via antenna applicators. The primary goal is to shape the power deposition (specific absorption rate, SAR) with focusing on the tumor region, and minimizing the risk of hotspots in the surrounding healthy tissues. Methods: For non-superficial tumors, phased-array antennas are used to focus the energy on the tumor. Finding patient-specific optimal antenna feeding coefficients represents an essential step to ensure an effective and safe administration of the heating. In this article, we present a way to optimize the array power transfer effectiveness (impedance matching) that does not deteriorate the spatial power deposition performance. A global optimization approach is adopted, using a cost function properly tailored to incorporate the active reflection coefficients of the array and the Hotspot-to-Target SAR Quotient (HTQ)—the latter being the standard in hyperthermia applications. Results: The effectiveness of the technique is demonstrated in a scenario relevant to the treatment of tumors in the neck region. The results show that our method significantly improves antenna matching without compromising the HTQ, achieving values within the recommended limits. The performance of the proposed approach is also experimentally tested with full heating in a corresponding phantom. Conclusions: This study introduces an optimization approach that enhances phased-array antenna performance for hyperthermia treatments without affecting spatial power deposition.

An electromagnetics-aware path for drone-based near-field antenna measurements is implemented in an outdoor experimentation. This technique allows to significantly reduce the scan duration with respect to a standard half-wavelength near-field scanning, using knowledge of the antenna under test electrical size only. The validity of our approach is corroborated with planar outdoor near-field measurements performed with an untethered drone transmitting at 750 MHz. To deal with the absence of phase coherence, the phase information is retrieved from a reference antenna, while a software-defined radio having four super-heterodyne receiving channels is used to properly sample the high-dynamic signals resulting from the large scanning surface.

We present a 3D method to numerically design a realizable metasurface, which transforms a given incident field into a radiated field that satisfies mask-type (inequality) constraints. The method is based on an integral equation formulation, with local impedance boundary condition (IBC) approximation. The procedure yields the spatial distribution of the impedance, yet the process involves the synthesis of the equivalent current only. This current is constrained to correspond to a realizable surface impedance, i.e., passive, lossless, and with reactance values bounded by practical realizability limits. The current-based design avoids any solution of the forward problem, and the impedance is obtained from the synthesized current only at the end of the process. The procedure is gradient-based, with the gradient expressed in closed form. This allows handling large metasurfaces, with full spatial variability of the impedance in two dimensions. The method requires no a priori information, and all relevant operations in the iterative process can be evaluated with O ( N log N ) complexity. Application examples concentrate on the case of on-surface excitation and far-field pattern specifications; they show designs of circular and rectangular metasurface antennas of 20 wavelengths in size, with pencil- and shaped-beam patterns, and for both circular and linear polarization.

The aim of the article is to provide a summary of the work carried out in the framework of a research project funded by the Italian Ministry of Research. The main goal of the activity was to introduce multiple tools for reliable, affordable, and high-performance microwave hyperthermia for cancer therapy. The proposed methodologies and approaches target microwave diagnostics, accurate in vivo electromagnetic parameters estimation, and improvement in treatment planning using a single device. This article provides an overview of the proposed and tested techniques and shows their complementarity and interconnection. To highlight the approach, we also present a novel combination of specific absorption rate optimization via convex programming with a temperature-based refinement method implemented to mitigate the effect of thermal boundary conditions on the final temperature map. To this purpose, numerical tests were carried out for both simple and anatomically detailed 3D scenarios for the head and neck region. These preliminary results show the potential of the combined technique and improvements in the temperature coverage of the tumor target with respect to the case wherein no refinement is adopted.

We describe a method to use numerical simulations concurrently with measurements (Near Field data) to characterize the radiation properties of an antenna (Far Field) with a strongly reduced number of samples. Both simulations and experimental data are dealt with as sources of information towards obtaining the desired characterization. Simulations compensate for data scarceness, allowing to obtain an accurate characterization with fewer data than with measurements only, and the few measured data allow the comprehensive numerical proxy to get tuned to the true antenna under test. The method uses partial knowledge of the antenna and leverages accelerated asymptotic numerical methods to perform the numerical simulations needed by the algorithm. We report experimental tests of performance, both in term of accuracy and speed-up with respect to classical methods, with reflector antennas up to 27 wavelength. It is important to note that good results are obtained both when samples are taken on irregular optimized grids and on the regular grids usually resulting from conventional measurement rigs.

A horizontal planar scanner with an approximate size of 40 m $\times40$ m has been implemented using the Unmanned Aerial Vehicle (UAV) technology. The UAV is not wired to the ground to maintain the flexibility and short setup time of a non-tethered flight. In this configuration, the UAV-mounted continuous-wave source is not phase-locked to the on-the-ground receiver. A dual-polarized reference antenna placed on the ground is hence used to retrieve the relevant phase information. The presented approach has been applied on the Pre - Aperture Array Verification System (Pre -AAVS1) of the Square Kilometre Array, which is a digital beamformed array with 16 active elements. An inverse source technique has been applied on measured Near-Field (NF) data acquired on two different sets of points (one for each electric field component) from all the receiver channels. In this way, Embedded Element Patterns (EEPs), array calibration coefficients and pattern have been determined from NF data only. The achieved results have been validated using a complementary set of Far-Field (FF) measurements and simulations.

The hypersonic flight regime is conventionally defined for Mach > 5; in these conditions, the flying object becomes enveloped in a plasma. This plasma is densest in thin surface layers, but, in typical situations of interest, it impacts electromagnetic wave propagation in an electrically large volume. We address this problem with a hybrid approach. We employ the equivalence theorem to separate the inhomogeneous plasma region from the surrounding free space via an equivalent (Huygens) surface and the Eikonal approximation to Maxwell equations in the large inhomogeneous region for obtaining equivalent currents on the separating surface. Then, we obtain the scattered field via (exact) free-space radiation of these surface equivalent currents. The method is extensively tested against reference results and then applied to a real-life reentry vehicle with full 3-D plasma computed via computational fluid dynamic (CFD) simulations. We address both scattering [radar cross section (RCS)] from the entire vehicle and radiation from the onboard antennas. From our results, significant radio link path losses can be associated with plasma spatial variations (gradients) and collisional losses to an extent that matches well the usually perceived blackout in crossing layers in the cutoff. Furthermore, we find good agreement with existing literature concerning significant alterations of the radar response (RCS) due to the plasma envelope.