ABSTRACT:The nonreciprocal properties of lossy GaAs magnetoplasma ridged parallel-plate waveguides are assessed at 250 GHz using a gyroelectric performance factor. The optimum phase shift for a twolayer structure is predicted when the magnetoplasma semiconductor is in a superstrate position with a low-permittivity dielectric substrate below a half-height ridge. This arrangement exhibits TEM to TM 01 mode conversion.