Any good softwares for simulating antenna efficiency?

I've tried HFSS ver.10 and it's efficiency simulation is way off the measurement from chamber...
any other candidates?

Take a look at the Antenna Modeling Design System

http://eesof.tm.agilent.com/products/amds_main.html [/url]

my friend work witch antennas used Feco.

Well, I don't think the problem is the software but how you model your antenna. What kind of an antenna are you simulating? The most critical part is how you model dielectrics and setup meshing and other parameters. Is the chamber calibrated?