high directivity stripline coupler

Does anyone know how to design a high directivity coupler such as wiggly line microstrip coupler,I need the formulas,Thank in advance!

If you want to design a coupler for instance with a broadside coupler or a coupled line (according to the coupling you desire) you have to take into account the different velocitu of odd mode and even mode. So if you want good directivity even with these structures you have to make equal the two velocity. Usually one can do this adding a capacitor at the beginning and at the end of the lines or even in the middle.
The equation are the same of the coupled lines
hoping this can help u
stefano

For lambda/4 microstrip couplers 25dB to 30dB directivity should be in reach with a little tuning.
Waveguide measurement couplers can have e.g. 50dB directivity. They need extensive tuning by hand.
Broadband couplers like in Vector-Network-Analyzers are good if they reach 15dB directivity.
Does it have to be a microsrip-coupler? What bandwith and directivity do you reach for?

Spasomat

It seems we can buy coupler that made by strip line technology,not
microstrip line.
What's the benefit ? lower loss & good directivity?

how to tuning?I want use stripline coupler but I don't make sure that the directivity in stripline coupler maybe better than a wiggly line microstrip coupler,does this right?

Thanks molly,for the reason of bandwidth,I don't want use capacitor to compensate the phase velocity.

there are some way to make it.

1) overlay coupler
2) if u r working nerow band , dont use 90 deg, use shorted one
3) put cap at the begin and the end of the coupler (u can put open stub)

good luck
elad