A Self-Aligning Cylindrical Sliding Short Plunger for Millimeter-Wave Rectangular Waveguides and Its Application in a Reflection-Type Phase Shifter

A sliding short for millimeter-wave rectangular waveguides and its dedicated application in a reflection-type phase shifter are presented. The design of the sliding short has self-aligning properties, where the correct and stable positioning of the sliding short on the central axis of a rectangular waveguide is guaranteed. Unwanted and disruptive waveguide wall contacts are avoided by design. Misalignment of the sliding short is only possible due to mechanical tolerances. This is systematically investigated by parametric full-wave simulations. Measurements of a W-band prototype yield a return loss better than 0.1 dB for offset positions from 0 to 1.5 mm throughout the whole W-band. A mechanical reference plane outside of the rectangular waveguide is used for correct and reproducible axial positioning of the sliding short in the waveguide. Mechanically measured offset positions and those retrieved from the reflected phase agree to a maximum error of 6 μm, which is within the manufacturing tolerance and the measurement uncertainty. Based on the proposed self-aligning sliding short, a reflection-type phase shifter has been realized, where a branch-guide coupler with a seven-slot design is used as broadband quadrature hybrid. Measurement results indicate an insertion loss in the range of 0.2 dB from 80 to 105 GHz and a maximum phase shift of 160° and 330° at 75 and 110 GHz, respectively.