In this contribution, we propose an innovative horn antenna design capable to filter undesired noise out. The radiator is based on a regular WR-62 horn, having a metallic screen inserted between the feeding waveguide and the flared aperture. We have drilled a vertical rectangular slit on the screen (the long side of the slit is in the E-plane) and placed a dielectric slab across the slit itself. On the two sides of the slab, we have printed metallic omega particles with appropriate dimensions in order to resonate in a sub-band of the operating frequency range of the WR-62 horn. At the particle resonance, signals are allowed to pass through the screen, reducing, thus, the operating frequency band of the WR-62 horn. This setup may find application in receiving systems of satellite communications, where signal bandwidths are rather narrow and noise captured by the antenna needs to be filtered out. This result is obtained keeping the same space occupancy of the regular WR-62 horn at the only expense of inserting a light and cheap dielectric board between the horn and its feeding waveguide. The idea is verified through proper full-wave numerical simulations and experimental results.