"The radio continuum spectra of Supernova Remnants (SNRs) is typically characterised by a simple synchrotron emission.
However, spectral slope changes, connected to the age and the evolution of the source in the interstellar medium, could characterise the high frequency radio spectra of evolved SNRs.
To disentangle possible electron acceleration mechanisms that could contribute at a spectral flattening/steepening, sensitive high-resolution images at high radio frequencies are required.
With this aim, we carried out multi-feed imaging observations of Tycho, W44 and IC443 at 21.4 GHz with the Sardinia Radio Telescope (SRT), providing a morphological and spectral description of these complex SNRs at radio frequencies that are so far unexplored, with a resolution below 1 arcmin.
Our flux density measurement on Tycho confirms the non-thermal synchrotron as the dominant emission process, ruling out any spectral curvature up to high radio frequencies, as expected for a young SNRs in its early Sedov phase.
Although W44 and IC443 are both classified as middle aged SNRs, our observations show different cut-off energies in their synchrotron spectra.
For the first time, we observed  a synchrotron spectral break in SNR W44 at a frequency of 14 GHz. This result provides a direct estimate of the maximum energy of accelerated cosmic-rays electrons of about 10 GeV, which is consistent with indirect evidence from AGILE and Fermi-LAT gamma-ray observations. 
With regard to IC443, our results confirm the presence of a bump in the integrated spectrum around 20−70 GHz that could result from a spinning dust emission mechanism.
Our high-resolution images allows us to study the spectral index associated with different peculiar regions of the SNRs.
Both in W44 and IC443 we observe a correspondence between bright-flat spectrum regions and gamma-ray emission that could represent a
signature of secondary electron populations produced by hadronic interactions in regions where the SNR shock collides with dense molecular clouds
"