Novel Millimeter Wave Transition From Microstrip Line to Groove Gap Waveguide for MMIC Packaging and Antenna Integration

In this letter, a new microstrip line to groove gap waveguide (GGW) transition has been proposed. The transition is based on a resonant cavity, which efficiently helps to couple the field from microstrip line to GGW. In this transition, the microstrip section is extended into the cavity without any requirement of contact with the GGW. Such contactless transition inside the waveguide is advantageous as it allows easy packaging and integration of millimeter wave circuitry with gap waveguide components such as filters and array antennas. Alumina (<inline-formula> <tex-math notation="LaTeX">$\epsilon _{r}=9.9$ </tex-math></inline-formula>) was used as the microstrip substrate for the proposed transition in this letter. Measured results for the <inline-formula> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula>-band transition show a relative bandwidth of 26% for a return loss better than 10 dB. The maximum insertion loss of the manufactured back-to-back prototype is found to be 1.32 dB, which also includes the losses of a 5.45-mm-long microstrip line on an Alumina substrate. After subtracting the losses in the microstrip section, the losses in a single transition are found to be varying between 0.145 and 0.38 dB over the bandwidth.