The authors present novel field-assisted photocathodes exhibiting an enhanced photoemission by nanoscale metallic grating antennas fabricated on the surface. The antennas serve to guide the incident photon fluxes into the nanoscale apertures of the photocathodes by the surface plasmon resonance. They demonstrate the comparisons of the spectral response characteristics between the calculated and experimental results. The nanoscale antennas would be utilized to realize a photocathode with extremely low dark current especially in the near infrared region.