Dear Kezman,
As you have not completely defined your requirements, I just can mention a presentation which includes a power divider with non-uniform power splitting ratio for output ports:
**broken link removed**
Anyway, for more efficient help, please let me know:
1) Is the relative phase of the outputs important?
2) What is the maximum power to be tolerated? (peak and average)
3) What is the maximum tolerable VSWR for 12-18 GHz?
4) What is the desired minimum efficiency?
Best regards
wave-maniac