Physics behind branch line coupler?

Hi
I am unable to understand how a branch line coupler works physically. By scattering matrix or even-odd mode it seems ok, but any physical explanation?
In case branch line as combiner when two signals applied at port 2 and 3 (say 0dbm at both ports) at port 1 we should get 0dbm, because from port3 to port 1 also loss is 3dB, but instead we get 3dBm at pot 1, why so? Is my understanding correct?
Can any one help me to answer my confusions.
Thank you

it could not be much more simple. Power comes in port 1, travels 2 ways. the power from both paths shows up in phase at the two outputs, and out of phase at the isolated port. That is why each leg is ~90 degrees long.

If you want an uneven split, you screw with the 90 degree sections to make the right impedance show up to split the power properly between the 2 ports.

Just draw one on a piece of paper, and draw what the phases would be at mid frequency arriving at the 3 ports from the input port.