100% “efficiency” is a numerical artifact usually boundary too close, port power misaccounted, or coarse local mesh around the feed/DRA interface causing tiny negative losses. Use PML + symmetry, fix the port, and add local mesh ops at the feed and DRA surface. Evaluate at the adaptive solution frequency. That will bring radiation efficiency back below 100% without breaking the Student mesh limit.

You're absolutely right—achieving over 100% efficiency is a common issue in all HFSS versions based on my experience. Last year, during a university collaboration project, I encountered this same challenge. The solution they implemented was to use two boundary boxes:

This approach effectively resolved the problem. Rafael Alex Vieira do Vale