Broadband suspended stripline to air-filled rectangular waveguide transition

A broadband transition between a suspended stripline (SSL) and a rectangular waveguide is presented. To improve the bandwidth of the transition, a U-shaped patch is introduced. A back-to-back transition prototype has been designed and fabricated for purpose of verification. Experimental results show that the transition has an insertion loss of less than 0.26 dB and a return loss better than 18.5 dB over the entire Ka-band (26.5-40 GHz), which agrees well with the simulated results. As compared with the SSL-to-waveguide transition using a reduced-height waveguide, the fractional bandwidth is increased from 29.5 to 40.9%. Moreover, with the reduced-height waveguide removed, the circuit structure has been simplified. The proposed transition provides a good performance while maintaining a simple circuit structure.