Hello gvinu4u,
For Branchline coupler it is always better to start with Circuit Design tools initial design & optimization & then simulating in Electromagnetic tools for accurate simulation...
I recommend AWR Microwave Office (MWO) which has good Microstrip/Stripline models library & integrated layout editor...which also has integreted em simulator for accurate analysis of passives...
Here is the document/article on Brachline coupler design procedure using MWO...
**broken link removed**
Also you can use other Circuit tools from Agilent ADS or Ansoft Designer, APLAC or Genesys,etc..
---manju---