A Broadband Millimeter-Wave Hollow Waveguide Coupling Structure Configured by a Wire-Eroded Metal Plug-In

The design of a WR 10 waveguide coupling structure is presented. Electrically, it consists of an E-plane (series) T-junction and a quarter-wave section. The resulting coupling factor is nearly constant over the entire W-band. A milled split-block network and a wire-eroded metal plug-in, which is inserted into a groove in the split block, implement the coupling structure. This modular design makes the coupling factor easily configurable and enables the realization of quarterwave section heights in the range of tens of micrometers. The plug-in is fabricated by wire erosion, a machining technique based on electrical discharge (spark machining). This enables precise adjustment of the height and length of the quarter-wave section (±2-μm contour accuracy) and provides polishedlike surface quality (R
_z
= 2.1 μm). Hints for the manufacturing of the metal plug-in are given; full-wave simulations as well as measurements of W-band prototype structures are evaluated, and the possibility of a postfabrication adjustment of the metal plugins is shown.