This work presents the design of a compact inline waveguide polarizer. The device is inspired by a polarizing frequency selective surface, which allows to significantly reduce the length of the designed waveguide polarizer. A circuit model of the frequency selective surface unit cell is established and used both to better explain the operating principle of the device and also to speed up the optimization process. A numerical example at C-band is presented, and the device performance is compared with other state of the art devices.