what are the differences between CST and Microwave office

CST Microwave Studio is an 3D EM simulator. It has time domain, frequency domain, thermal, and solver for scattering problems. They also have some packages for magnetics and particles.

Microwave office is a general purpose circuit simulator. It has solvers for 2.5D closed boundry EM, 2.5D gridless open boundry EM (soon to be released), linear, harmonic balance, HSPICE, and system simulation via VSS. It ties all these together with extraction methods for EM and mappings between time and frequency domains. It can handle simulations and layouts from PCBs to Si RFICs. It has an open EM interface that hooks to CST, Sonnet, and many others.

tnx for fast answer , but what is the difference between EM simulator and circuit simulator ?[/youtube]

EM Simulator: given geometry, material, boundary, solve the "Maxwell's equations" for Electric and Magnetic fields.

EM simulator is a strcture simulator which gives S,yandz parameter and also 3D radiation pattern ,field distribution etc.