[help] about directive couplers

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caocao

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Hi every one,
I want to design a directivity couplers of 20dB in 1~2GHz,It is a very mature tech but for me it is new!I design a kind of microstrip lines which is intered between two dielectrical layer,but its directivity is only 13dB,the desire goal is >20dB.I think the coaxial type is a good one ,who can tell me some design methods about coaxial one,and give me some papers on them.
Thanks very much!
Regards
caocao
 

you don't have to give up on microstrip. there are ways to equalize the even and odd mode phase velocities to improve the directivity. look at the attachment for the possibilities. the attachment is taken from a book on coupled line circuits. of course, you can always go with the TEM approach and not have to deal with this problem.
 

Hi Frannk
thanks for you advices and posted figure about microstrip couplers, but could you offer me the whole papaer about the sawtooth coupling of microstrip or tell where could download the paper.
I had simulated the microstrip between two layer with same Er,but when the coupling is 20dB,the directivty is also poor (15dB). I want to know which method could improve directivity.
Thanks！
Regards
caocao
 

Hi caocao,
Why you don't use Stripline Configuration. It is TEM medium and has equal velocity of even and odd mode. 35dB directivity with this config. can be implemented simplicity.

KMPA
 

Here is my master thesis part 1 and it is very relating to your request

Directional coupler from 0 _12 GHz
 

This also the 2nd part of my Master Thesis could be value for you
 

Here's a paper on arc type microstrip couplers with relatively high directivity.

**broken link removed**

Also, here are the pages from the Artech book on couplers regarding the discussed topic.
 

Almost all commercial coupler are made on stripline rather than ustrip.
In stripline, due to higher possibility to get more coupling, the mechanical tollerance are less critical.
 

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