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This paper presents the electromagnetic design of part of a receiver passive front-end at C band (4.2–5.6 GHz) to be used for radio astronomy applications. The front-end devices here shown are a circular corrugated horn, a differential phase shifter and an orthomode transducer, which are required to study the circular polarization content of the sky signal. All of these components are developed in waveguide technology, best suited for high sensitivity receivers. Design and fabrication aspects are presented and test results discussed.

Here we present evaluations of the systematic effects induced by flat isotropic dielectric slabs by using the Mueller matrix formalism. We find that isotropic dielectrics can produce spurious polarization either when transmit anisotropic diffuse radiation or are not thermally uniform. We will provide detailed analysis for the 32 GHz@10% band case, but some results about 90 GHz@20% and 150 GHz@30% bands will be also shown. To support the analytical approach we have performed some measurements of the return loss of a teflon slab confirming the theoretical forecast.

We describe the optical design and optimisation of the Low Frequency Instrument (LFI), one of two instruments onboard the Planck satellite, which will survey the cosmic microwave background with unprecedented accuracy. The LFI covers the 30–70 GHz frequency range with an array of cryogenic radiometers. Stringent optical requirements on angular resolution, sidelobes, main beam symmetry, polarization purity, and feed orientation have been achieved. The optimisation process was carried out by assuming an ideal telescope according to the Planck design and by using both physical optics and multi-reflector geometrical theory of diffraction. This extensive study led to the flight design of the feed horns, their characteristics, arrangement, and orientation, while taking into account the opto-mechanical constraints imposed by complex interfaces in the Planck focal surface.

The BaR-SPOrt (Balloon-Borne Radiometers for Sky Polarization Observations) experiment, a program of the Agenzia Spaziale Italiana (ASI) co-funded by PNRA (Progetto Nazionale di Ricerca in Antartide) was originally designed as a payload for long duration balloons flights. The changing scenario, both scientific and strategic, has led us to propose it for the starting winter campaign of at the Concordia Base. Here the instrument and the features making it suitable to operate at Dome-C are described. After the initial setup, BaR-SPOrt should not require any kind of routine intervention by a dedicated base staff. The experiment will just need electrical power (less than 2 kW) and a suitable accommodation on the field. It can be fully monitored and controlled, including the data acquisition, through its own telemetry/telecommand link using IRIDIUM modems. Both the receiver and the critical electronics are housed inside a temperature-controlled vacuum chamber, providing the properly stabilized environment. The cold part of the radiometer employs a closed loop mechanical cryo-cooler that provides temperatures < 70 +/- 0.1 K with low power consumption (< 200 W).

The measure of the faint polarized signal of the Cosmic Microwave Background (few percent of the CMB Anisotropy) requires instruments with very low contamination from systematic effects, high stability and high sensitivity. The BaR-SPOrt experiment, in sharing with the SPOrt project on ISS, is based on analog correlation receivers with components custom designed to match all of these requirements. Here we present the architecture, the design analysis and the status of the realization of the 32 GHz receiver.