Receiver's Radiometric and Optical Optimization for Solar Observations in W-Band

Solar eruptive phenomena occurring during periods of intense magnetic activity can affect Earth's technological infrastructure, including telecommunications, space facilities and aeronautical operations. Observations at radio frequencies provide important diagnostics of these events and may reveal forecasting signatures useful for Space Weather. However, the extended W-band (67–116 GHz) remains largely unexplored for solar monitoring. The aim of this thesis is to develop and characterize a receiver capable of observing solar activity in the W-band within the framework of the Solaris project, a network of single-dish antennas located in Italy and Antarctica designed to provide monitoring of the Sun. Within this context, the Elegant Bread-Board n.2 (EBB2) receiver was assembled and experimentally characterized. The analysis included VNA measurements, linearity tests and the estimation of receiver gain and noise temperature through Y-factor techniques through dedicated Python routines. The receiver showed a linear behaviour both under quiet Sun and simulated flare events conditions. The receiver was then installed on the 1.5m Solaris test antenna in Milano, enabling the first experimental solar observations in the 80–110 GHz range. In addition, the optical configurations of the Milano and ROSA antennas were modeled using GRASP to simulate beam patterns and evaluate their impact on solar observations. Python-based convolution routines were used to simulate observations using real solar temperature maps and synthetic flare signals of varying intensities. An optimization study of the ROSA feed illumination identified an edge taper of −15 dB as the best compromise between angular resolution, sidelobe levels and antenna efficiency. These results establish the EBB2 as a validated prototype for future solar-dedicated receivers and lay the groundwork for the next phase of Solaris, which will deliver unprecedented Space Weather forecasting capabilities at microwave frequencies.