  We investigate the polarization properties of high harmonics generated with
the bichromatic counterrotating circularly polarized (BCCP) laser fields by
numerically solving time-dependent Schr\"odinger equation (TDSE). It is found
that, the helicity of the elliptically polarized harmonic emission is reversed
at particular harmonic orders. Based on the time-frequency analysis and the
classical three-step model, the correspondence between the positions of
helicity reversions and the classical trajectories of continuum electrons is
established. It is shown that, the electrons ionized at one lobe of laser field
can be divided into different groups based on the different lobes they
recombine at, and the harmonics generated by adjacent groups have opposite
helicities. Our study performs a detailed analysis of high harmonics in terms
of electron trajectories and depicts a clear and intuitive physical picture of
the HHG process in BCCP laser field.
