  Fast electron beams (FEBs) are common products of solar active phenomena.
Solar radio bursts are an important diagnostic tool in the understanding of
FEBs as well as the solar plasma environment in which they are propagating
along solar magnetic fields. In particular, the evolutions of the energy
spectrum and velocity distribution of FEBs due to the interaction with the
ambient plasma and field when propagating can significantly influence the
efficiency and property of their emissions. In this paper, we discuss some
possible evolutions of the energy spectrum and velocity distribution of FEBs
due to the energy loss processes and the pitch-angle effect caused by the
magnetic field inhomogeneity, and analyze the effects of these evolutions on
electron cyclotron maser (ECM) emission, which is one of the most important
mechanisms of producing solar radio bursts by FEBs. The results show that the
growth rates all decrease with the energy loss factor $Q$, but increase with
the magnetic mirror ratio $\sigma$ as well as with the steepness index
$\delta$. Moreover, the evolution of FEBs also can significantly influence the
fastest growing mode and the fastest growing phase angle. This leads to the
change of the polarization sense of ECM emission. In particular, our results
also reveal that FEB that undergoes different evolution processes will generate
different types of ECM emission. We believe the present results to be very
helpful on more comprehensive understanding of dynamic spectra of solar radio
bursts.
