  Although interesting in themselves, extragalactic sources emitting in the
microwave range (mainly radio-loud active galactic nuclei and dusty galaxies)
are also considered a contaminant from the point of view of Cosmic Microwave
Background (CMB) experiments. These sources appear as unresolved point-like
objects in CMB measurements because of the limited resolution of CMB
experiments. Amongst other issues, point-like sources are known to obstruct the
reconstruction of the lensing potential, and can hinder the detection of the
Primordial Gravitational Wave Background for low values of $r$. Therefore,
extragalactic point-source detection and subtraction is a fundamental part of
the component separation process necessary to achieve some of the science goals
set for the next generation of CMB experiments. As a previous step to their
removal, in this work we present a new filter based on steerable wavelets that
allows the characterization of the emission of these extragalactic sources.
Instead of the usual approach of working in polarization maps of the Stokes'
$Q$ and $U$ parameters, the proposed filter operates on E- and B-mode
polarization maps. In this way, it benefits from the lower intensity that,
both, the CMB, and the galactic foreground emission, present in B-modes to
improve its performance. To demonstrate its potential, we have applied the
filter to simulations of the future PICO satellite, and we predict that, for
the regions of fainter galactic foreground emission in the 30 GHz and 155 GHz
bands of PICO, our filter will be able to characterize sources down to a
minimum polarization intensity of, respectively, 125 pK and 14 pK. Adopting a
$\Pi=0.02$ polarization degree, these values correspond to 169 mJy and 288 mJy
intensities.
