Planar cross-polarized transition to a circular waveguide feed for a 61 GHz dielectric antenna

This paper presents a novel concept for a planar cross-polarized transition to a 61 GHz dielectric lens antenna. The transition to the circular waveguide antenna feed consists of a combination of a microstrip line and a slot line. Each of these planar waveguides excites the H₁₁ mode in the circular waveguide with a 90± polarization angle to one another. The developed double layer transition topology was realized on a Rogers 5880 substrate employing the microstrip line on the top and the slot line on the bottom layer. The concept was implemented and tested on a circular waveguide-fed dielectric lens antenna for a 61 GHz radar system. Experimental results show a transition loss of around -2 dB for the microstrip and -3 dB for the slot line feed with excellent crosstalk suppression greater than 40 dB for the two polarization channels. The bandwidth of the built crosspolarized transition is greater than 10 GHz. The results prove that the novel transition concept is very well suited for compact, broadband and low cost polarimetric millimeter-wave radar systems.