Andrea Martellosio

One of the critical points concerning radio-astronomy applications regards the power received by the radio telescope, most often extremely faint. Beyond approaches aimed at increasing the collecting area of the radio telescope (at microwave frequencies almost always a reflector antenna), such as for example the use of very long baseline interferometry (VLBI) techniques, a key point is the installation of cryogenic receivers to reduce the system noise temperature. To achieve the lowest noise temperature, it is desirable to cryogenically cool also the feed of the reflector antenna. This is achieved by enclosing the feed in a Dewar to provide the required thermal isolation between the feed and the external environment. However, this enclosure inevitably affects the radiation properties of the feed. This letter presents the development of a cryogenic receiver, composed of a 2-14 GHz quad ridge flared horn and a Dewar, for a notable case where the Dewar is designed to be as compact as possible to minimize not only the thermal and mechanical load, but also the illumination blockage. Indeed, the receiver is intended to be installed on a 12 m reflector antenna for VLBI applications, whose optics require an installation of the feed itself very close to the subreflector. A prototype of the cryogenic receiver has been fabricated and measured, discussing the impact of the Dewar on the feed radiation patterns, input matching, isolation, antenna efficiency, and showing the overall system noise temperature.

Satellite communications with the ability to provide a downlink channel with high bit rates are needed, and this need is driving frequency upscaling toward bands higher than the X band. A number of these satellites requires ground stations at the polar region, which are usually protected against the harsh environment using radomes.

Cancer affects a significant percentage of people, and early detection techniques are important for prompt and effective treatment. The use of microwave frequencies to achieve non‐invasive and non‐destructive cancer detections is currently under investigation by several research groups. In this frequency range, the dielectric properties of the biological tissue determine the interactions of the tissue with electromagnetic fields. Knowledge of the dielectric properties of both the normal and the malignant human tissues is therefore a fundamental starting point. A dielectric spectroscopy system, based on the use of a reflectometry setup, was used to perform an extensive experimental campaign on fresh surgical specimens. The measurement system allowed achieving a broadband dielectric characterisation of biological tissues up to 50 GHz, thus including millmetre‐wave (mm‐wave) frequencies. In the case of breast tissues, the results showed that the malignant and normal tissues exhibit significantly different complex dielectric permittivities of up to 50 GHz, due to their respective high and low water content. This permittivity difference is well detectable, and this paves the way to new screening methods based on mm‐wave imaging systems.