A metasurface based on a fishnet-like unit cell is designed, realized, and measured at terahertz frequencies through time-domain spectroscopy in reflection mode. While most of fishnet-like metasurfaces are designed in the resonant regime (i.e. with and , being the period and the free-space wavelength), the proposed one is designed in the homogenized regime (i.e. with ). Experimental results show that the proposed metasurface exhibits very high reflectivity, which makes it particularly attractive for the design of high-gain Fabry–Perot cavity leaky-wave antennas.