SUMMARY
In marine and coastal radar applications it is usual to find antennas consisting of a slotted waveguide antenna and a horn antenna. To increse the effectiveness of the cuban coastal surveillance system, it is proposed to modify the AU11-07N slotted waveguide antenna of the Navy-Radar 4000 based on the design of an optimal pyramidal horn antenna, causing the half power beamwidth to be reduced by half in the vertical plane. To archive the objective, the original antenna is measured and modeled to then simulate in the Ansoft HFSS software and compare it with the data from the radar manual. Then, the original antenna is modified based on the design of an optimal pyramidal horn, simulated and adjusted to the final dimensions based on the variation in the length of its plates. With the proposal modification, the half power beamwidth is archived to the vertical plane of 11.30 degrees and for the horizontal plane of 0.71 degrees, a secondary lobe level of -35dB for the azimuth plane and a final gain of 34 dB, greater than that of the original antenna.