  We model the evolution of active galactic nuclei by constructing their radio
luminosity functions. We use a set of surveys of varying area and depth, namely
the deep COSMOS survey of $1,916$ AGN sources, the wide shallow 3CRR, 7C and
6CE surveys, containing together $356$ AGNs, and the intermediate XXL-North and
South fields consisting of $899$ and $1,484$ sources, respectively. We also
used the CENSORS, BRL, Wall $\&$ Peacock and Config surveys, consisting
respectively of $150$, $178$, $233$ and $230$ sources. Together, these surveys
numbered $5,446$ AGN sources and constrained the luminosity functions at high
redshift and over a wide range of luminosities (up to $z \approx 3$ and $\log
(L / \mathrm{W Hz^{-1}}) \in [22,29])$. We concentrate on parametric methods
within the Bayesian framework and show that the luminosity-dependent density
evolution (LDDE) model fits the data best, with evidence ratios varying from
"strong" ($>10$) to "decisive" ($>100$) according to the Jeffreys
interpretation. We determine the number density, luminosity density and kinetic
luminosity density as a function of redshift, and observe a flattening of these
functions at higher redshifts, not present in simpler models, which we explain
by our use of the LDDE model. Finally, we divide our sample into subsets
according to the stellar mass of the host galaxies in order to investigate a
possible bimodality in evolution. We found a difference in LF shape and
evolution between these subsets. All together, these findings point to a
physical picture where the evolution and density of AGN cannot be explained
well by simple models but require more complex models either via AGN
sub-populations where the total AGN sample is divided into subsamples according
to various properties such as, for example, optical properties and stellar
mass, or via luminosity-dependent functions.
