  The so-called zebra structures in radio dynamic spectra, specifically their
frequencies and frequency drifts of emission stripes, contain information on
the plasma parameters in the coronal part of flare loops. This paper presents
observations of zebra structures in a microwave range. Dynamic spectra were
recorded by Chinese spectro-polarimeters in the frequency band close to the
working frequencies of the Siberian Solar Radio Telescope. The emission sources
are localized in the flare regions, and we are able to estimate the plasma
parameters in the generation sites using X-ray data. The interpretation of the
zebra structures in terms of the existing theories is discussed. The conclusion
has been arrived that the preferred generation mechanism of zebra structures in
the microwave range is the conversion of plasma waves to electromagnetic
emission on the double plasma resonance surfaces distributed across a flare
loop.
