In the paper, a novel wideband three-dimensional polarization-rotating spatial filter (3-D PRSF) is proposed by utilizing a slotline-microstrip-slotline coupling scheme, capable of rotating a linearly polarized incident wave by 90° over a wideband frequency range. To streamline the design process, a transmission-line based circuit model is first established and synthesized with the Chebyshev function. Following the synthesis approach, the circuit parameters can be directly obtained from the design specifications of return loss (RL) and fractional bandwidth (FBW). As an example, a fourth-order 3-D PRSF with RL of 10 dB and FBW of 80% is designed, whose physical parameters are accurately determined by the corresponding circuit parameters. To validate the concept, the designed 3-D PRSF is fabricated and measured. The measured results closely align with the predicted responses.