The Effelsberg 100-m telescope is an alt-azimuthal Gregorian single-dish radiometer, which performs obervations in the range 0.3-100 GHz. The feed horns are installed at the primary or at the Gregorian focus, according to the observed frequency, and typically supplies circularly polarized outputs which are processed by two total power detectors and two multiplying polarimeters. In order to obtain all the four Stokes parameters, the outcoming signals (Left circular, Right circular, Stokes Q, Stokes U) must be combined during a post-processing calibration procedure, that corrects for the cross-talk between the outputs (Müller matrix correction). The instrumental polarization is calibrated by observing the planetary nebula NGC7027, assumed to be unpolarized, and the QSO 3C286, as strongly linearly polarized calibrator.
So far, full Stokes observations have been performed in continuum mode at 2.7, 5, 8.5, 10 GHz, obtaining typical accuracies of nearly 1 mJy in CP and 8 mJy in LP, after 15 minutes of integration time.
The Michigan 26-m telescope is an equatorially mounted primary focus single dish radiometer. Linear and circular polarizations are obtained by means of rotating double feed horn systems, equipped with quarter-wave plates (tapered slabs of plastic inserted in the horn). At the vertex of the parabolic mirror a noise diode transmits a signal through a polarizing grid, which is aligned with respect to the North pole. Periodical observations of the transmitted polarized signal guarantee the correct orientation the wave plates. By switching between the two horns (on-off technique) and between the orthogonal modes of the main horn (through the rotation of the system), all the four Stokes parameters are obtained. The instrumental polarization is calibrated by observing galactic HII regions, assumed to be unpolarized.
Typical accuracies achieved, after some hours of integration time, are of the order of 0.05-0.2%, for strong sources (I>5Jy).
The Medicina 32-m telescope is a Cassegrain single-dish radiometer, which performs obervations in the range 1.4-22 GHz. The feed horns are installed at the primary or at the Cassegrain focus, according to the observed frequency, and the receiver architecture is analogous to that of the Effelsberg one.
The performance of the antenna during a full Stokes observations has still to be tested (proposal submitted on April, 1st 2010).