A novel noncontacting waveguide backshort has been developed for millimeter wave and submillimeter wave frequencies. It employs a metallic bar with rectangular or circular holes. The size and spacing of the holes are adjusted to provide a periodic variation of the guide impedance on the correct length scale to give a large reflection of rf power. This design is mechanically rugged and can be readily fabricated for high submillimeter wave frequencies where conventional backshorts are difficult or impossible to fabricate. Model experiments have been performed at 4 GHz – 6 GHz to empirically optimize the design parameters. Values of reflected power greater than 95% over a 30% bandwidth have been achieved. A specific design is presented which has also been successfully scaled to WR-10 band (75 GHz – 110 GHz). A theoretical analysis is compared to the experiments and found to agree well with the measured data.
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