Facing Power Combining Problem of Power Amplifier at final stage

[narayani]

Initially I have taken two ideal amplifiers and combined power and later 4 ideal PAs and combined power and finally 8 ideal PAs and combined the power. When I Combined 2 ideal PAs and 4 ideal PAs, I didn't face any problem of combining power.
But when I have taken 8 PAs and combined power, everything works nicely till the last Branch Line coupler. At the Last Branch Line Coupler, it is giving same output power of previous stage Branchline Coupler outputs. I have shown in the screen shot of obtained output power.
Why at the last stage PAs BranchLine(BLs) Coupler is not combining input powers. Before all BLs except last BLs are combining power smoothly. What is the mistake in the last BL?

 

[volker@muehlhaus]

Don't forget that you coupler requires 90° phase offset between the ports. Replace your final coupler with two ports, and check phase difference between the two paths.

edit: I checked your topology, with through line instead of the amplifier staged, and everything look ok there. S21=0dB at one output port, the other port is isolated.

 

[volker@muehlhaus]

I tried to reproduce your model including the 20dB amplifiers and the levels that you used, and everything looks ok !?