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In this paper we describe the design and characterization of the optical system of LSPE/Strip, a coherent polarimeter array that will observe the microwave sky from the Teide Observatory in Tenerife in two frequency bands centred at 43 and 95 GHz through a dual-reflector crossed-Dragone telescope of 1.5 m aperture. In general, optical systems composed by a telescopefeed array assembly have non-idealities that might limit their ability to perform high-precision measurements. It is thus necessary to understand, characterize and properly control these systematic effects. For this reason, we performed electromagnetic simulations to characterize angular resolution, sidelobes, main beam symmetry, polarization purity and feedhorns orientation. The results presented in this paper will be an essential input for further optical studies and for the LSPE/Strip data analysis. Ultimately, they will be used to assess the impact of optical systematic effects on the scientific results., 18 pages, 13 figures

This paper reports the design, manufacturing and testing of the cluster of polarizers developed for the LSPE-Strip correlation receiver array working in the Q band (39–48 GHz). Since the LSPE experiment targets the measurement of the very faint B-mode component of the Cosmic Microwave Background, the electromagnetic design of the polarizers was conceived in view of minimizing the measurement uncertainties introduced by the polarizers in the LSPE-Strip dual-circular-polarization correlation receiving chain. To this end, the main figures-of-merit of the LSPE-Strip polarizers were derived in terms of the Mueller sub-matrices relating the relevant input and output Stokes parameters. As a result, a dual-ridge layout, in which stepped-ridge discontinuities are interleaved with grooved cavities, was selected. The heights of both the stepped discontinuities and the grooved cavities were considered as design degrees of freedom in order to minimize the differential phase-error between the two principal polarizations of the polarizer w.r.t. the ideal 90-deg value. The latter condition is the one required for converting the incoming circular polarizations into two linearly polarized ones. The polarizer design allows for a complete manufacturing route (mechanical layout, machining process and assembling) exhibiting high accuracy (< 10 μm) for all the units. As a consequence, the measured performance of the whole polarizer cluster is in tight agreement with predictions. Notably, the in-band mean value of the spurious conversion from the total intensity I to the two linearly polarized Stokes parameters Q and U introduced by the polarizers is smaller than -28 dB (mean value of fifty-one polarizers) with a standard deviation less than 1 dB.

In this paper we discuss the Planck-LFI in-flight calibration campaign. After a brief overview of the ground test campaigns, we describe in detail the calibration and performance verification (CPV) phase, carried out in space during and just after the cool-down of LFI. We discuss in detail the functionality verification, the tuning of the front-end and warm electronics, the preliminary performance assessment and the thermal susceptibility tests. The logic, sequence, goals and results of the in-flight tests are discussed. All the calibration activities were successfully carried out and the instrument response was comparable to the one observed on ground. For some channels the in-flight tuning activity allowed us to improve significantly the noise performance., Comment: Long technical paper on Planck LFI in flight calibration campaign: 109 pages in this (not final) version, 100 page in the final JINST version