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Latest observational reports of solar flares reveal some uncommon features ofmicrowave spectra, such as unusually hard (or even positive) spectra, and/or asuper-high peak frequency. For a better understanding of these features, weconduct a parameter study to investigate the effect of broken-power-law spectraof energetic electrons on microwave emission on the basis of gyrosynchrotronmechanism. The electron broken-power-law energy distribution is characterizedby three parameters, the break energy ($E_B$), the power-law indices below($\delta_1$) and above ($\delta_2$) the break energy. We find that with theaddition of the $\delta_2$ component of the electron spectra, the total fluxdensity can increase by several times in the optically-thick regime, and byorders of magnitude in the optically-thin regime; the peak frequency ($\nu_p$)also increases and can reach up to tens of GHz; and the degree of polarization($r_c$) decreases in general. We also find that (1) the variation of the fluxdensity is much larger in the optically-thin regime, and the microwave spectraaround the peak frequency manifest various profiles with the softening orsoft-hard pattern; (2) the parameters $\delta_1$ and $E_B$ affect the microwavespectral index ($\alpha$) and the degree of polarization ($r_c$) mainly in theoptically-thick regime, while $\delta_2$ mainly affects the optically-thinregime. The results are helpful in understanding the lately-reported microwavebursts with unusual spectral features and point out the demands for amore-complete spectral coverage of microwave bursts, especially, in thehigh-frequency regime, say, $>10-20$ GHz.

Gyrosynchrotron emission generated by nonthermal electrons with energy spectra of a broken power law