how to icrease the directionality of wideband coupler?

[amicloud]

I used 2-stage coupled stripline to realize 800MHz-2500MHz couler.but the
directionality is about 20dB.
now a customer has a need for diretinality of 30dB,how to realize?

 

[vfone]

Directivity [dB] = Isolation [dB] – Coupling [dB]
So, to increase the directivity, in your simulation you have to increase Isolation or to decrease Coupling, keeping the other one constant.
Some theory about directional couplers:
**broken link removed**
**broken link removed**

 

[biff44]

Thats a big bandwidth for 2 sections. Try more sections. You might get better directivity with some lumped elements between sections. Really investigate the matches at your connector launches, and especially the internal 50 ohm load.

 

[borich_03]

If you want to have good directivity, you must execute good matching for all loads in your design.

 

[sergio mariotti]

Also if you increase the intimate directivity of the directional coupler, the reflections due to connectors and launcher, and in general the loads will became dominant.
20 dB is a good value for common (industry) coax connectors.
30 db and more require precision connectors and very low VSWR loads.
In other worlds, directivity is not a performance dominated by the Coupler alone, but depend on the external match also.