Impedance Measurements in Waveguides Below Cutoff

A measurement set-up is described which is capable of measuring impedances in below-cutoff waveguides. Due to the strong attenuation of the fundamental mode, this circuit technique presents inherent difficulties to impedance measurements which are overcome by properly designing the probes and by inserting dielectric-filled propagating line sections into the waveguide below cutoff. It is finally shown, how this set-up can be applied to a systematic design of passive and active components.