The antenna–plasma coupling for the ITER low-field side reflectometer system (LFSR) was studied using the hybrid 3D reflectometer simulation code FWR3D, in which full-wave, paraxial, and free-space solvers are used for speed and accuracy. Reflections from equilibrium profiles were simulated to study and optimize the power that is coupled the receiving antenna. At the optimal coupling, the effects of density fluctuations were also calculated, showing that the density fluctuations decrease the average coupling by as much as 6 dB. This study indicates that after some minor changes to the location of the proposed antennas, the antenna–plasma coupling of the ITER LFSR provides a sufficient basis from which to design and build a reflectometer system that meets the specifications requested by ITER.