I want to know how to design a nonreciprocal waveguide. I'm not sure if the only difference between these two waveguides is only the material used to design them.
Thats right, It is mainly the reciprocity of the material which determines the reciprocal waveguide behavior. On the other hand, in non-reciprocal waveguide the materials do not satisfy the reciprocity condition. Example: Ferrites biased by a DC magnetic field.