Metasurface is a two-dimensional form of metamaterial that is ultra-thin in volume and light in weight and capable of controlling the polarization state of electromagnetic waves; nevertheless, it has a very small bandwidth. We offer a terahertz (THz) metamaterial with several transmission-mode-operating dielectric layers that may, over a wide frequency range, convert polarized light. The suggested polarization quarter wave plate (WP) is effective throughout a broad frequency range, including 0.85 to 2.45 THz, with a low insertion loss of 2.57 dB and an ultrabroad bandwidth approaching 1600 GHz when the angle of polarized incidence is 45 deg. Regarding the impacts of shapes, elliptical pillar geometries, and the quantity of dielectric layers, the effectiveness of polarization conversion are also investigated. The proposed WPs are highly suited for use in THz optical systems due to their ultrathin subwavelength thickness. Furthermore, the relationship between the number of layers and bandwidth based on the multi-layer elliptic cylinder results in novel transmission phase properties that increase the likelihood of polarization control of incident waves over a wider bandwidth.