  A catalogue of 14453 radio-loud AGN with 1.4 GHz fluxes above 3.5 mJy in the
redshift range 0.4<z<0.8, has been constructed from the cross-correlation of
the NVSS and FIRST radio surveys with the MegaZ-LRG catalogue of luminous red
galaxies derived from Sloan Digital Sky Survey imaging data. New techniques
were developed for extending the cross-correlation algorithm to FIRST
detections that are below the nominal 1 mJy S/N limit of the catalogued
sources. We estimate a reliability of ~98.3%, and completeness level (for LRGS)
of about 95% for our new catalogue. We present a new determination of the
luminosity function of radio AGN at z~0.55 and compare this to the luminosity
function of nearby (z~0.1) radio sources from the SDSS main survey. The
comoving number density of radio AGN with luminosities less than 10^{25} W
Hz^{-1} increases by a factor ~1.5 between z=0.1 and z=0.55. At higher
lumiosities, this factor increases sharply, reaching values of more than 10 at
radio luminosities larger than 10^{26} W Hz^{-1}. We then study how the
relation between radio AGN and their host galaxies evolves with redshift. Our
main conclusion is that the fraction of radio-loud AGN increases towards higher
redshift in all massive galaxies, but the evolution is particularly strong for
the lower mass galaxies in our sample. These trends may be understood if there
are two classes of radio galaxies (likely associated with the "radio" and
"quasar mode" dichotomy) that have different fuelling/triggering mechanisms and
hence evolve in different ways.
