# directional coupler - coupling factor S31, help needed in calculation

#### Omri Shachak

Joined Mar 27, 2018
11
hello to all,
For a project i am doing i need a coupler with around 10 dB = S31. The problem is that i am very limited in what i can manufacture. I can only use a directional coupler of the form of coupled lines with a certain gap, and material etc. (which gives me around 15dB = S31).
I saw an article (which i add below) that gave me the idea of connecting two identical couplers. like this:

Now my problem is what is the difference in the coupling factor of the combined two couplers?
I chose the suitable phases (lengths of phi1,phi2) in order to get a full constructive interference.
is it the coupling factor difference between my single coupler and the double coupler is 6 dB or 3 dB?
when i read the article and think about it in terms of power i think that the difference is 3dB. But when i think about it like an interference between two voltages i get double the voltage and therefore 4 times as much power in the coupling port in the double coupler in relation to the coupling port in a single coupler which is 6 dB.

#### Omri Shachak

Joined Mar 27, 2018
11
The article

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