  Rydberg atomic sensors and receivers have enabled sensitive and traceable
measurements of RF fields at a wide range of frequencies. Here we demonstrate
the detection of electric field amplitude in the extremely high frequency (EHF)
band, at $131\ \mathrm{GHz}$. In our approach we propagate the EHF field in a
beam, with control over its direction and polarization at the detector using
photonic waveplates. This way, we take advantage of the highest detection
sensitivity, registered for collinear propagation and circular polarization. To
exhibit the potential for applications in this kind of Rydberg-atom based
detection, we perform test measurements on the EHF field emitted from an
on-chip radar, planned to be used in automotive industry as a vital sign
detector. Our work elucidates practical applications of Rydberg-atom media as
well as photonic metamaterial elements.
