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how to using ADS or other software to design a 3-dB coupler?

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Advanced Member level 4
Mar 3, 2002
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In this forum,I think there have many expert on coupler design.but how to just use software, such as ads2002 or microwave office to design a 3-dB stripline coupler?I use mutilayer model of ads2002,but the result seems not very good.wish expert give me some advice.
Best regards,

What is the frequency of your stripline 3dB coupler?
And What is the Substrate you use?
3dB is a Strong Coupling
So you should design it carefully

Are you making a Power spliter? /\ D S has a wilkinson power spliter
example in their design kit. I built a (3dB)Branch line coupler in /\DS, using Monentum but the results where not very accurate. A few things to remember
are the wave length in the substrate you are using and the trace width for
50 Ohms at your center frequency. You can find many app notes on the web.

Hope this helps

paper and pencil

The wilkins and branch line couplers are so well understood that you should be able to design them with paper and pencil and use the software to verify the design. You can do a frequency sweep to see where the design works best and then scale the lenghts to move the best performance part to the frequency you want.

The main errors you will probably have to look out for as mentioned above is the impedance of the lines and the wavelength. Rogers corp has a free calculator for determining the impedance and velocity at a given frequeny.

Here is a copy of their program.

Thx so much for your all help.
For my design,the bandwidth is from 2GHz~6GHz,I want use two 8.34-dB coupler to form a tandem 3-dB coupler,so the branch-line coupler sames not appropriate for this design.Do you have any advice?


Lange coupler

The Lange coupler is the type which will give you these bandwdiths.

You might also be able to use a two or three section wilkinson in series using stepped impedance. This will give you better bandwidth. I did a two section one that covered 1-2GHz. That's 100% bandwidth. If you have @DS, look in @DS\examples\training\*omentum\mom_class_prj and you will see a nice single section splitter.


I am seeing some printed balun with ADS (schematic and momentum) and I see that the simulation on microstrip balun (rat race or Marchand) are very good (I measured the s-parameter of these baluns in some boards and the results are very closed to the simulation). Now I am trying to explore new tipology in CPW-slotline structure in ADS in order to reduce the dimensions of these balun, but I have a lot of problem because the results are differents from the article where I take this tipology (I think to simulate the CPW-slotline structure I need a three dimension simulator). Do you know other tecnique (balun over two or three layers for istance) to reduce the balun dimension?


If your design is based on edge couplers, then you can create multiple fingers. This will make a very small balun. But if I remember correctly, the output ports are 90degrees, not 180 so if you need 180, you will need an additional 90 degree external phase shift. What are you tryng to do?

Thx,my design is based on broside couple, and I want the phase error must less than 90+/- 2 degree,amplitude error less than 0.5 dB at 2GHz~6GHz,so I think lange is not a good choice.

HI toonafishy

I am trying to design a balun for the W-LAN 802.11a standard (5 to 6 GHz). I designed a rat race for this application with very good results, but the dimensions are good for research and not for an application board. So I am exploring new structure to design a wideband balun but with little dimensions. I am trying with CPW-slotline structure but I can't simulate it correctly with Momentum of ADS: is it for my mistake? Do you know other structures very low in dimension but with a large bandwidth?


Have a look at this design which includes ADS files for dowload.
**broken link removed**

Just one question for coupler expert people,

A branch-line coupler is a 4 port component. The output ports (O1 and O2) are loaded with 2 equal loads at -15 dB each one...
The question is: how much is the return loss at the input and at the other port?
I think that theorically I can have -

(sorry.. some problem occured..) I was saying:

-infinite dB at input port and -9 dB at the other port.
What do you think?


Hi Needbias,

I have make a 4-8Ghz 3dB coupler with tow five step coupler,
in my view, the step uncontinues is very important. The ads and mw not consider their step uncontinues and coupling in same time.
So, you can try it in ads momental or ansoft ensemble.
finally,I get -2.5 to -3.5 dB coupler in full band.

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