We perform a quantum-orbit analysis for the dependence of high-order-harmonic yield on the driving field ellipticity and the polarization properties of the generated high harmonics.The electron trajectories responsible for the emission of particular harmonics are identified It is found that, in elliptically polarized driving field, the electrons have ellipticity-dependent initial velocities, which lead to the decrease of the ionization rate.Thus the harmonic yield steeply decreases with laser ellipticity.Besides, we show that the polarization properties of the harmonics are related to the complex momenta of the electron.The physical origin of the harmonic ellipticity is interpreted as the consequence of quantum-mechanical uncertainty of the electron momentum.Our results are verified with the experimental results as well as the numerical solutions of the time dependent Schr(o)dinger equation from the literature.