The vector image code (VIC) consisting of the vector transmission cross coefficient (TCC) and Fourier transform of the mask function is widely applied to simulate the effects of polarization in microlithography. Until now studies were restricted to the effects of linear polarization. This Linear polarization illumination predicts a larger contrast gap between TE polarization and TM polarization as the numerical aperture increases or the critical dimension decreases. In this article, we have studied the effects of elliptical polarization illumination (EPI) as a new method in order to decrease these contrast gaps. We improved VIC by adopting EPI including circular polarization. As a result of using the improved VIC, EPI shows that the contrast and the contrast gap can be tuned by adjusting the angle of polarization and the ratio of the ellipticity. The simulation result also shows that the higher the ratio of ellipticity the lower the contrast gap but at the expense of lowering the contrast somewhat. If this new EPI is adopted into microlithography, the contrast gap can be decreased while the contrast to a specified direction of the mask pattern can be kept high.