Quasioptical millimeter-wave measurements: Refractive index of thin plates

The refractive index of dielectric sheet materials (polystyrene, polypropylene) and of paraffin is measured at mm-wave frequencies using the specimens as dielectric slab waveguides. The mode wavelengths are measured in the evanescent field outside the slab of monomode and two-mode waveguides in which stationary interference patterns of modal fields are generated. The accuracy of the method is about 0.5%.