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 mm to 1.5 mm throughout the whole Wband. 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 7-slot design is used as broadband quadrature hybrid. Measurement results indicate an insertion loss in the range of 0.2 dB from 80 GHz to 105 GHz and a maximum phase shift of approx. 160 • and 330 • at 75 GHz and 110 GHz, respectively. Index Terms-Micromachining, millimeter-wave passive components, phase shifters, millimeter-wave circuits, millimeter-wave devices, waveguide components I. INTRODUCTION S TEERABLE phase shifting circuits are needed in a variety of applications such as adaptive tuning units or beamsteered phased array antennas. There are numerous mechanical and electronic technologies to realize a passive variable phase shifter. These can generally be categorized by three prevailing topologies: Switched-line, loaded-line, and reflection-type phase shifters. In switched-line phase shifters, the electrical length from the input to the output port is changed by internally switching between waveguides of different length. PIN diodes, field-effect transistors or microelectromechanical Manuscript received Month dd, yyyy; revised Month dd, yyyy. The authors express their gratitude to the Helmholtz Association of German Research Centres for funding this work within the framework of the Helmholtz Virtual Institute on "Plasma Dynamical Processes and Turbulence Studies using Advanced Microwave Diagnostics". They are also indebted to the foreman of the precision mechanical workshop Josef Franzisi for helpful suggestions and Clemens Moroder for initial investigations towards a millimeter-wave reflection-type phase shifter.
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