Design of microwave subsystems for radio astronomical receivers

The radio astronomical receivers are devices that they measure the radio emissions coming from celestial sources. Therefore, the aim of these devices is to convert the weak electromagnetic energy from space into a measurable electrical signal. The nature of the signal emitted by celestial sources imposes that such receivers must be broadband, very sensitive and designed to measure noise. In fact, the electromagnetic signal that the receivers must capture and measure, in addition to being very weak, is a random signal with components uncorrelated with each other, with different frequencies and with zero mean value (i.e. it is like the thermal noise produced by a resistor subject to a temperature). Therefore, the weakness and the peculiarity of these signals make the radio astronomy receivers other than those used in the telecommunications. It is in this context that the work of my PhD thesis has been developed. Three different projects, that regard to the microwave subsystems of the radio astronomical receiver, have been treated. The first project is focus on the development of a new configuration of broadband polarizer with very flat phase response in microtrip technology. The second project is a feasibility study on the optics of a 3mm SIS receiver in order to install it in the Gregorian focus of the Sardinia Radio Telescope. The third project is fully dedicated on the development of a high performance wideband feed-horn for a state-of-the-art multi-beam S-band (2.3 - 4.3 GHz) receiver to install in the primary focus of the Sardinia Radio Telescope.