A dual mode rotary joint as described herein can be utilized in an electromagnetic communication system such as a radar system. The dual mode rotary joint can be used to rotatably couple an antenna architecture to its mounting structure. One embodiment of the dual mode joint includes a waveguide configured to propagate radio frequency (RF) signals, and endcaps coupled to the ends of the waveguide. Each endcap is reflective for RF signals and transmissive for optical signals.