Design and Validation of Microstrip Gap Waveguides and Their Transitions to Rectangular Waveguide, for Millimeter-Wave Applications

The paper describes the design methodology, experimental validation, and practical considerations of two millimeter-wave wideband vertical transitions from two gap waveguide versions (inverted microstrip gap waveguide, and microstrip packaged by using gap waveguide) to standard WR-15 rectangular waveguide. The experimental results show S11 smaller than -10 dB over relative bandwidths larger than 25% and 26.6% when Rogers RO3003 and RO4003 materials are used, respectively. The vertical transition from standard microstrip line packaged by a lid of pins to WR-15 shows measured return loss better than 15 dB over 13.8% relative bandwidth. The new transitions can be used as interfaces between gap waveguide feed networks for 60-GHz antenna systems, testing equipment (like vector network analyzers), and components with WR-15 ports, such as transmitting-receiving amplifiers. Moreover, the paper documents the losses of different gap waveguide prototypes compared with unpackaged microstrip line and substrate integrated waveguide (SIW). This investigation shows that in V-band, the lowest losses are achieved with inverted microstrip gap waveguide.