A Millimeter-Wave Isolator Containing a Semiconductor Rod in a Circular Waveguide

Attenuation characteristics of an InSb waveguide isolator at 94 GHz and 75 K are given experimentally and theoretically. The structure is a rod of InSb placed coaxially in a circular waveguide. Operation of the device depends on changes of both absorption and cutoff wavelength in the structure with direction of propagation of a circularly polarized signal. Over 20-dB isolation is measured with 3-dB forward loss.