Author:
Peverini O.A.,Lumia M.,Farooqui Z.,Addamo G.,Virone G.,Paonessa F.,Ciorba L.,Zannoni M.,Gervasi M.,Franceschet C.,Bersanelli M.,Mennella A.,Cuttaia F.,Morgante G.,Villa F.,Jones M.
Abstract
Abstract
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.
Subject
Mathematical Physics,Instrumentation