During many years the RATAN-600 radio telescope is used for the intensive studies of the active galactic nuclei (AGNs) at frequencies from 1 to 30 GHz. Comparison of the data with other bands from the millimeter wavelengths to gamma-rays allowed to recognize the evolution of AGNs which obviously relates with the process of accretion on the supermassive black holes.
Meanwhile geometric interpretation of activity variety of AGNs is in the good agreement with their statistical properties the common AGN theory does not exist yet. Acceleration of charged particles up to ultrahigh energy occurs in the internal relativistic shock waves running through jets of AGN. Relativistic electrons in inhomogeneous jets emit synchrotron radio emission which is variable and linearly polarized.
Joint researches AGNs in the total electromagnetic band provide a more complete picture of activity in the central regions of galaxies.
The main advantage of monitoring program of AGNs with the RATAN-600 radio telescope is simultaneous measurements of the radio spectrum in the wide frequency range from 1 (from 2006 before 2011) to 30 GHz for a relatively numerous samples of sources (figure 1). Determination of the properties of rapid and long-term variability of cosmic radio sources is a effective way to understand the nonstationary processes of accretion of matter onto the black holes.

Figure 1. Time-frequency evolution of the flux density for two BL Lacertae type object B0235+16 and 3C454.3. Experimental data were obtained with using radio telescope RATAN-600 during 2006-2011.