Well, it depends on the structure you wanna make, I had worked wave guide and cavity resonator on High frequency structure simulator (HFSS) it was perfect, you could also design an antenna on the same program :)    

Check this review paper, it might be useful (... though it focuses on simulation in manufacturing) http://www.sciencedirect.com/science/article/pii/S0928486998000226.

HFSS is the best ... works on finite element technique...

try to use CST, it has a lots of functions 

You have some options CST, COMSOL, ADS + momentum, AWR... If you interested in just rectenna design u should use momentum+ADS or CST/HFSS.

People usually use ADS for rectifier design, and use CST, momentum or HFSS designing rf passive circuits (filter, impedance matching, antenna etc.) when designing rectenna. 

Try COMSOL Multi-physics