If you are designing complex networks of power dividers, combiners and couplers using standard structures like common transmission lines, coupled lines, etc. what you need is a circuital software. A good starting point is QUCS, which is simple and free. Qucs project: Quite Universal Circuit Simulator
If you are designing not networks, but specific elements where circuital models don't provide a good enough accuracy, you need a electromagnetic software. In this case, there are not many free simulators. May you can try Sonnet. Sonnet Lite
thank u very much for ur reply,please suggest any simulators for designing of power combiners ,power dividers,directional couplers at microwave frequencies and also basic information about designing.
Are these microwave circuits are based on planar transmissionline implementation such as microstrip/stripline/cpw?
If so use Sonnet Lite 13.51 which is free electromagnetic simulator based on Method of Moments.... Free Download - Sonnet Lite
HFSS for planar circuits makes not much sense. Why not use a planar solver, which is more accurate for planar model and easier to use by any means (stackup, port defintions).