rf to dc conversion

I am doing a project that converts rf power to dc power. Currently i am looking at the possible simulation software to study various voltage doubler designs and is pondering whether pspice or ads should be a more appriopate software for use.

Harmonic balance is going to be allot faster than SPICE for this type of problem assuming it converges OK. In addition you will want to play around with the driving source impedance so that's easier to do in an RF simulator. If you want to simulate a DC-DC converter then you will need SPICE.

I am also a user of CST. I am wondering is it possible to make use of design studio for simulation?

It probably is since Microwave Studio supports diodes in it's transient simulator. I have never tried it and I'm guessing you will manually have to calculate efficiency and other parameters. Nonetheless it is pretty neat to have diodes in an EM simulator.