  Supernova remnants (SNRs) represent a powerful laboratory to study the
Cosmic-Ray acceleration processes at the shocks, and their relation to the
properties of the circumstellar medium. With the aim of studying the
high-frequency radio emission and investigating the energy distribution of
accelerated electrons and the magnetic field conditions, we performed
single-dish observations of the large and complex Cygnus Loop SNR from 7.0 to
24.8 GHz with the Medicina and the Sardinia Radio Telescope, focusing on the
northern filament (NGC 6992) and the southern shell. Both regions show a
spectrum well fitted by a power-law function ($S\propto\nu^{-\alpha}$), with
spectral index $\alpha=0.45\pm0.05$ for NGC 6992 and $\alpha=0.49\pm0.01$ for
the southern shell and without any indication of a spectral break. The spectra
are significantly flatter than the whole Cygnus Loop spectrum
($\alpha=0.54\pm0.01$), suggesting a departure from the plain shock
acceleration mechanisms, which for NGC 6992 could be related to the ongoing
transition towards a radiative shock. We model the integrated spectrum of the
whole SNR considering the evolution of the maximum energy and magnetic field
amplification. Through the radio spectral parameters, we infer a magnetic field
at the shock of 10 $\mu$G. This value is compatible with a pure adiabatic
compression of the interstellar magnetic field, suggesting that the
amplification process is currently inefficient.
