A new waveguide method for measuring the permittivity of dielectric slabs

The paper describes a new waveguide method for measuring the complex relative permittivity of dielectric slabs. The slab is mounted in rectangular waveguide either on the waveguide axis or in contact with the side wall. One end of the slab contacts a fixed short-circuit plate. By using a standing-wave detector, the condition is found for the guide wavelength in the dielectric section to equal the free-space wavelength. A simple expression enables the real part of the permittivity to be calculated. From observations of the standing-wave ratio, the attenuation coefficient in the dielectric-loaded waveguide is determined. Another simple expression then enables the imaginary part of the permittivity to be calculated. The theory of the method is developed and illustrated with results obtained using a polystyrene slab.