  We present a new evolutionary model that describes the population properties
of radio sources at frequencies <5 GHz, thus complementing the De Zotti et al.
(2005) model, holding at higher frequencies. We find that simple analytic
luminosity evolution is still sufficient to fit the wealth of available data on
local luminosity functions, multi-frequency source counts, and redshift
distributions. However, the fit requires a luminosity-dependent decline of
source luminosities at high redshifts, at least for steep-spectrum sources,
thus confirming earlier indications of a "downsizing" also for radio sources.
The upturn of source counts at sub-mJy levels is accounted for by a
straightforward extrapolation, using the empirical far-IR/radio correlation, of
evolutionary models matching the far-IR counts and redshift distributions of
star-forming galaxies. We also discuss the implications of the new model for
the interpretation of data on large-scale clustering of radio sources and on
the Integrated Sachs-Wolfe (ISW) effect, and for the investigation of the
contribution of discrete sources to the extragalactic background. As for the
ISW effect, a new analysis exploiting a very clean CMB map, yields at a
substantially higher significance than reported before.
