The invention relates to a surface sensor (100, 200), comprising a frequency-selective surface with periodically arranged THz structures (1), in particular THz resonance structures (1) which are sensitive to THz radiation, a polarization axis (3) being associated with each structure. In order to improve remote field characteristics, the invention provides for a THz structure (1) to be configured asymmetrically, and a group of two or more THz structures (1) to have essentially centrosymmetrically aligned polarization axes (3) for forming a unit cell.