Logic of coupling value in tandem 3dB connection

[yefj]

Hello,In a 3dB coupler we have a property where between the output we have 90 degree phase.
We can construct the 3dB coupler by taking two 8.34dB couplers as shown in the article bellow.
But in the article page 2,we have a calculation where they take 45 degrees and get 3dB from that?
What is this 45 degrees? is it somehow linked to our 90 degree property ?
Thanks.

https://link.springer.com/content/pdf/10.1007%2F978-3-642-35155-6_55.pdf

 

[BradtheRad]

Could this have to do with the principle that a series capacitor causes a phase shift of an incoming sinewave? At the frequency where 3dB attenuation occurs, the phase shift appears to be about 45 degrees, advance.
However two parallel networks both advance the phase so net effect is zero, not 90 degrees differential. Anyway I don't claim to understand the MultiSection Broadside Stripline Tandem Structure.