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 $p\simeq\lambda,\ p$ and $\lambda$, being the period and the free-space wavelength), the proposed one is designed in the homogenized regime (i.e. with $p\ll\lambda$). 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.