Polarization of RCS (Bit of double jeopardy, sorry)

Hello all,

I wanted your opinion on what Ansys means in one of their user guides. Concerning a radar cross section measurement, they define a sweep on an incident plane wave in spherical coordinates. They say the polarization is phi directed. How would you interpret that? Where do you think k and Eo point?

for better context: slide 13
ogiveGSG.pdf

thanks,
Sami