The proliferation of X and Ku band applications in satellite communications, remote sensing, radar systems, and in ever-increasing wireless networks, impels to design of an ultra-wideband reflection-based linear polarization converter. An efficiently designed converter enhances the signal quality in addition to minimizing the interferences in wireless links. Seeing these upcoming myriad number of applications, in this paper, we design and fabricate a lightweight ultra-wideband converter structure by utilizing two 0.15 mm thin FR-4 sheets and a Teflon air-spacer having a thickness of 5.25 mm. Specifically, the top side of the unit cell consists of a diagonally arranged parallel metallic strip printed on thin FR-4 substrate material which is separated by a Teflon spacer with complete metal on the bottom side. To show the efficacy, numerical simulations are performed and the obtained results are validated by fabricating the device in the lab. The experimental and simulation results show that the proposed structure works as a cross-polarizer with a polarization conversion ratio of more than 90% in the C, X, and Ku bands with an operating range of 6.2-16.6 GHz. The measured co-reflection coefficient of the fabricated device completely matched with the simulated reflection coefficient which corroborates with the obtained results. The proposed structure features a sub-wavelength-sized unit cell ((Formula presented.)), which significantly enhances the angular stability of the design. Additionally, it achieves an impressive fractional bandwidth of 91.2% and is characterized by its lightweight structure, making it highly efficient for various applications, such as radiometers and RCS reduction.