One of the main drawbacks of complex horn antennas is that their analysis can result costly in computational terms. However, this cost can be mitigated by employing smart segmentation strategies that enable an efficient analysis of the different parts composing the antenna. Then the partial results can be merged in order to obtain the response of the whole antenna. The present work illustrates this analysis approach by presenting different simulation strategies for a monopulse horn antenna design in W-band (operation frequency 94 GHz) with triple radiation pattern, a -14 dB beamwidth of 24 degrees for the sum pattern (and 12 degrees for the difference patterns) and a return loss higher than 20 dB.