Medical imaging currently relies on several techniques, including X-rays, magnetic resonance, and echography. However, these techniques exhibit drawbacks, and alternative approaches are required. Microwave imaging has been proposed as a possible solution, especially for breast cancer imaging. However, most of these systems work with a central frequency of a few gigahertz, and this leads to a suboptimum resolution, which can jeopardize the image quality. Millimeter waves can provide superior resolutions, at the cost of a lower penetration depth within the breast tissue. In addition, a significant fraction of the power generated by a mm-wave imaging system would be reflected back from the skin. For these reasons, and also considering that mm-wave transmitters and receivers have been historically outperformed by microwave counterparts in terms of available power and sensitivity, mm-wave imaging has not been considered a possible solution. This paper contributes to demonstrate a paradigm shift toward the possible use of mm-waves for breast cancer imaging of targets a few centimeter below the skin, a useful penetration depth for several cases. All key points are addressed using analytical, full-wave, and multiphysics simulations, including the system architecture (linear and conformal), the safety aspects (power density, specific absorption rate, and temperature increase), and the use of realistic breast models derived from ex vivo measurements.

Nowadays, breast cancer is the most diffused disease among women around the word. Statistics indicate an increase in incident rate, especially in Europe, North America, and Oceania. Currently, the set of diagnostic tools for breast cancer detection is wide. Nevertheless, these tools exhibit limitations, especially when aiming at cost-effective periodical mass screenings. Therefore, there is a growing interest toward microwave imaging systems for biomedical applications, and several microwave prototypes have been proposed worldwide. However, in order to have a satisfying resolution for earlydiagnosis, microwaves may be not sufficient, and a crucial point is the utilization of higher frequencies. To this aim, as the physical principle of all imaging techniques at these frequencies is based on the detection of the dielectric discontinuities between materials, the characterization of all breast tissues in the mmwave spectrum becomes fundamental. No experimental data were available beyond 20 GHz before the two extensive experimental campaigns performed at the European Institute of Oncology in 2014 and 2016. In this paper, the results concerning the full database (given by the fusion of the two datasets) of exvivo samples, are presented. In particular, a huge amount of data is considered, involving more than 330 samples, of which 237 healthy and 99 malignant, taken from around 100 women with an age spanning from 28 years up to 85 years.

The effectiveness of radar interferometric techniques in non-urban areas can often be compromised due to the lack of stable natural targets. This drawback can be partially compensated through the installation of reference targets, characterized by a bright and stable radar response. The installation of passive corner reflectors (PCR) often represents a valid aid, but these objects are usually cumbersome, and suffer from severe weather conditions; furthermore, the installation of a PCR can be difficult and costly, especially in places with hard accessibility. Active reflectors (AR) represent a less cumbersome alternative to PCRs, while still providing a stable phase response. This paper describes the design, implementation, and test of an AR prototype, designed to operate with the Sentinel-1 synthetic aperture radar (SAR), aimed at providing a fair performance/cost benefit. These characteristics, obtained through a tradeoff between the use of off-the-shelf components and a simple architecture, can make the setup of a dense network (i.e., tens of devices) in the monitored areas feasible. The paper reports the design, implementation, and the analysis of different tests carried out in a laboratory, and in a real condition in the field, to illustrate AR reliability and estimate its phase stability.

Breast cancer is one of the leading causes of death among women in the world. In recent years, there has been an increase in the incidence rate, but the rate of death has decreased. This is due to the improvement of diagnostic techniques, which are making possible to have diagnoses ever more precocious. However, all the techniques currently in use show limitations (such as the use of ionizing radiation) and therefore new imaging techniques are being studied. Microwave and millimeter waves imaging systems, based on the different behavior of healthy and tumorous tissues in the interest band, are seen as a viable alternative, so it is crucial to characterize the different human breast tissue up to 50 GHz. In 2014, in collaboration with the European Institute of Oncology in Milan, Italy, and in a project funded by the Italian Association for Cancer Research, a first experimental campaign on ex-vivo samples was conducted. In this paper, the results of a second experimental campaign, conducted in 2016 by the same team, are shown.

Determining snow water equivalent (SWE) in a fast and nondestructive way is a key request for many hydrologists and snow scientists. To this aim, microwave ground-based radars represent a viable solution, but often the simultaneous measurement of both the snowpack depth and density (the key ingredients for the SWE) is very complex, inaccurate, or requires difficult procedures and equipment. This letter presents a novel radar technique for self-standing calculation of the SWE that can be applied to bi-static radars. This technique, based on the multipath propagation of the radar signal into the snowpack, only requires a radar with two fixed antennas, without any other device, movement of the antennas, or a priori empirical assumptions. This makes such a technique particularly suitable for light and portable radars for rapidly probing large areas, providing, for example, an innovative validation means for satellite-based microwave remote sensing methods. The proposed technique was demonstrated using a stepped frequency modulated continuous wave (FMCW) radar in field conditions for dry snow, delivering results for snow depth and SWE, benchmarked by manual analyses of the snowpack, with a mean absolute error better than 5 cm.