Designing a broadband, wide-angle, and high-efficient polarization converter with a simple geometry remains challenging. This work proposes a simple and computationally inexpensive method for devising broadband polarization conversion metasurfaces. We focus on a cross-shape configuration consisting of two bars of different lengths connected at the center. To design the metasurface, we decompose the system into two parts with two orthogonally polarized responses and calculate the response of each part separately. By selecting the parameters with a proper phase difference in the response between the two parts, we can determine the dimensions of the system. For designing broadband polarization conversion metasurfaces, we define a fitness function to optimize the bandwidth of the linear polarization conversion. Numerical results demonstrate that the proposed method can be used to design a metasurface that achieves a relative bandwidth of\documentclass[12pt]{minimal}
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				\begin{document}$$97\%$$\end{document}97%for converting linearly polarized waves into cross-polarized waves. Additionally, the average polarization conversion ratio of the designed metasurface is greater than\documentclass[12pt]{minimal}
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				\begin{document}$$91\%$$\end{document}91%over the frequency range of 10.9–28.5 GHz. This method significantly reduces the computational expense compared to the traditional method and can be easily extended to other complex structures and configurations.