Hi all!

I'm having a warning from ADS when simulating a dual directional coupler: "warning detected by hepeesofsim during SP analysis. Linear S_Port 'Coup1.cmp2' is non passive".

I'm using manufacturer's data for the coupler and the warning is the same for an envelope analysis or S parameter analysis.

Any help will be appreciated.

I'm having a warning from ADS when simulating a dual directional coupler: "warning detected by hepeesofsim during SP analysis. Linear S_Port 'Coup1.cmp2' is non passive".

I'm using manufacturer's data for the coupler and the warning is the same for an envelope analysis or S parameter analysis.

Any help will be appreciated.

Coupling = 10 dB

VSWR for both coupled and main arms = 1.3

Loss = 0.2 dB

Directivity = 25 dB

Temperature = 25Â°C

The simulation set up: S-parameter analysis from 1 GHz to 2 GHz.

Thanks for your help.

A network with scattering matrix is passive [see ref.] iff,

(a) S*(s)=S(s*), â€˜*â€™ is the complex conjugate operator.

(b) S(s) is bounded real, i.e. ||S(s)||2â‰¤1 (where ||.||2 represents 2-norm).

Condition (a) is automatically satisfied since the complex poles are always considered along with their conjugates for microwave circuits such as couplers. For condition (b) we will use the s-parameters values from ADS and prove that for certain conditions the behavioral coupler may not necessarily obey this rule.

With the coupler parameters perovided the s-parameter results at 1 GHz are:

Â .1304 Â Â Â .9181 Â Â Â i*.3162 Â Â .001778

Â .9181 Â Â Â .1304 Â Â Â 001778 Â Â Â i*.3162

Â i*.3162 Â Â .0017782 Â .1304 Â Â Â 0

Â .001778 Â Â i*.3162 Â Â 0 Â Â Â Â Â .1304

which has Â a 2-norm of 1.1283 which clearly violates condition (b).

If you increase the loss to 1.7 dB, this was the smallest loss I found that meets passivity in ADS (i.e. gets rid of the passivity warning), the results are:

Â .1304 Â Â .7725 Â Â i*.3162 Â .0178

Â .7725 Â Â .1304 Â Â .0178 Â Â i*.3162;

Â i*.3162 Â 0.0178 Â Â .1304 Â Â 0

Â .0178 Â Â i*0.3162 Â 0, Â Â Â .1304

which has Â a 2-norm of 0.9923 which satisfies condition (b).

Reference:

"Restoration of passivity in s-parameter data of microwave measurements" Saraswat, D.; Achar, R.; Nakhla, M.; Microwave Symposium Digest, 2005 IEEE MTT-S International 12-17 June 2005 Page(s):1131 - 1134

I read the MTT-S paper with great interest. I understand why we have the non-passivity warning. I've got two more questions however :

- Is it just a "passivity check" problem or does it mean that my system using the coupler is wrongly modeled in ADS with such data? Are directional couplers modeled using S-parameters in ADS?

- Do you think the model will be appropriate for a transient envelope simulation ?

Regards

--

Divitha.

Just think about it, can you get or design a dual directional coupler that has the same coupling factor over all frequencies? Is it realistic? You most likely answered no, but for certain frequency domain analysis it is just fine to do so.

It sounds like the vendor was being a bit agressive on his coupler specifications. But he could always market it as the world's only coupler with Gain!