Lange coupler: mom and measurement difference.

[Manjunatha_hv]

Dear rautio,


Many Thanks, for the detailed explaination on circuit Analysis using Shielded/unshielded EM tools...
Yes you are right the three primary experiments are very much required to understand EM simulators...

1. Effect of Box Size
2. Effect of Cell Size and
3. Effect of Port De-embedding


---manju---

 

[Grig]

Dear Rautio

Can You upload your papers about error sources in EM analysis?
Please

Thanks

Added after 26 minutes:

Dear EXPERTS
Some years ago I seen lange coupler, it was fabricated on 500 um Lumina (ε~9.6-9.8),
Geometry was 4-finger, w=70 um s=50 um central freq~7GHz, metal t~5 um (Copper)
Measurement result was ~1dB overcoupled, but software results (I used MWO, ADS MOM, Ansoft Serenade) were ~0.5 dB under coupling
My conclusion was "the fabrication is not accurate", but there was no possibility to check w, s, and t . Than I'm interesting "has anybody seen the same problem with Lange".

Regards

 

[VSWR]

New ADS 2005A now also models horizontal currents on side walls. See

http://eesof.tm.agilent.com/products/ads2005a_new_13.html

What's about accuracy of ADS2004 momentum modeling of thick metal current distribution.

 

[rautio]

To check the accuracy on any EM tool for any aspect of the modeling, simply refine the mesh and see how the result changes.

For any thick metal model, you must refine the mesh in all three dimensions. For surface meshing, this is easy to do for X-Y (horizonta) metal, just make the cell size smaller.

For the Z-dimension in Sonnet thick metal, just increase the number of sheets (one click, type one number, re-analyze).

For the tube-like model, the vertical side sheets (with current flowing along the length of the line), you need to refine the meshing on the vertical sheets...kind of a vertical edge meshing. This because current is highest near the corners, regardless of whether the sheet is vertical or horizontal. Second, you also need to add more sheets on the interior of the metal, both vertical (parallel to the side sheets), and horizontal (parallel to the top and bottom sheets). This is because current pentrates into the metal due to skin effect. This moves current away from the surface of the thick metal and into the interior. To check for convergence, you must include this effect. This can be important, for example, when the gap between two coupled lines is on the order of the skin depth. The effective width of the gap is increased by current penetrating into the metal away from the gap surface. To find out if this is important, do a convergence analysis (as I just described) and find out. If you can not do such a convergence analysis, the accuracy will remain unknown, i.e., you are taking your chances...good luck.

Also, with the tube-like model, special consideration must be made for low frequency, where the skin depth is about equal to or larger than the thickness. In this case current is flowing in the entire volume, not just on the surface. This is most important when line width is on the order of line thickness. To check, simply do a square cross section line at very low frequency. This is a resistor and you can calculate the exact resistance easily. Compare with the value that comes out of the EM analysis.

The tube-like model will be most accurate when the skin depth is small compared to metal thickness and metal width, actually a fairly common situation so it is useful. But, as with all models of anything, they all break down at some point. It is important to know where that point is...assuming you want to keep your job!

Two papers I have published specifically about extremely thick metal modeling:

James C. Rautio, "A Space-Mapped Model of Thick, Tightly Coupled Conductors for Planar Electromagnetic Analysis," IEEE Microwave Magazine, Vol. 5, No. 3, September 2004, pp. 62 - 72.

James C. Rautio, "Accurate and Efficient Analysis of Large Spiral Inductors with Thick Metal and Narrow Gaps Using Space Mapping," IEEE MTT-S International Microwave Symposium, Workshop Notes & Short Courses - WFD-7, 6-11 June 2004.

As for my papers on error:

James C. Rautio, "Testing Limits of Algorithms Associated with High Frequency Planar Electromagnetic Analysis," European Microwave Conference Digest, Munich, October 2003, pp. 463 - 466.

James C. Rautio and Veysel Demir, "Microstrip Conductor Loss Models for Electromagnetic Analysis," IEEE Transactions on Microwave Theory and Techniques, Vol. 51, No. 3, March 2003, pp. 915 - 921.

J. C. Rautio, "An Investigation of Microstrip Conductor Loss," IEEE Microwave Magazine, Volume 1, Number 4, December 2000, pp. 60-67.

Erik H. Lenzing and James C. Rautio, "A Model for Discretization Error in Electromagnetic Analysis of Capacitors," IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 2, February 1998, pp. 162-166.

G. L. Matthaei, J. C. Rautio, and B. A. Willemsen, "Concerning the influence of housing dimensions on the response and design of microstrip filters with parallel-line couplings," IEEE MTT Transactions, Vol. 48, August 2000, pp. 1361 –1368.

James C. Rautio and George Matthaei, "Tracking Error Sources in HTS Filter Simulations," Microwaves and RF, Vol. 37, No. 13, December 1998, pp. 119 - 130.

J. C. Rautio, "An Investigation of an Error Cancellation Mechanism with Respect to Subsectional Electromagnetic Analysis Validation," International Journal of Microwave and Millimeter-Wave Computer-Aided Engineering, Vol. 6, No. 6, November 1996, pp. 430-435.

J. C. Rautio, "The Microwave Point of View on Software Validation," IEEE Antennas and Propagation Magazine, Vol. 38, No. 2, April 1996, pp. 68-71.

J. C. Rautio, "An Ultra-High Precision Benchmark For Validation Of Planar Electromagnetic Analyses," IEEE Tran. Microwave Theory Tech., Vol. 42, No. 11, Nov. 1994, pp. 2046-2050.

J. C. Rautio, "Experimental Validation of Electromagnetic Software," International Journal of Microwave & Millimeter-Wave Computer-Aided Engineering, Vol. 1, No. 4, Oct. 1991, pp. 379-385.

J. C. Rautio, "Experimental Validation of Microwave Software," 35th ARFTG Conference Digest, Dallas May 1990, (Voted best paper at the conference.), pp. 58-68.

In addition, the December issue of IEEE Microwave Magazine will have a paper I have written together with IBM on a potentially common measurement error for on-wafer Si RFIC measurements. This one could be pretty significant if you do RFIC.

I have not posted these papers because I am not sure about the copyright situation. Most of the above papers can be downloaded from IEEE Xplore, available to all IEEE members and at most engineering university libraries. I will be glad to send a pdf for any paper (if I have it) listed above, just send me an email and I will reply with the paper. And remember, salespeople are interested in accuracy. Engineers are interested in error.

 

[Grig]

Dear Rautio

My e-mail is mipt@ngs.ru
Send me following pdf papers if it's possible, Please

James C. Rautio, "A Space-Mapped Model of Thick, Tightly Coupled Conductors for Planar Electromagnetic Analysis," IEEE Microwave Magazine, Vol. 5, No. 3, September 2004, pp. 62 - 72.
James C. Rautio, "Accurate and Efficient Analysis of Large Spiral Inductors with Thick Metal and Narrow Gaps Using Space Mapping," IEEE MTT-S International Microwave Symposium, Workshop Notes & Short Courses - WFD-7, 6-11 June 2004.
J. C. Rautio, "The Microwave Point of View on Software Validation," IEEE Antennas and Propagation Magazine, Vol. 38, No. 2, April 1996, pp. 68-71.
J. C. Rautio, "Experimental Validation of Microwave Software," 35th ARFTG Conference Digest, Dallas May 1990, (Voted best paper at the conference.), pp. 58-68.

Thanks

 

[rautio]

Hi Grig -- Sorry for the delay. Not much gets done this week in the US due to very important holiday tomorrow. I just emailed three of the papers you requested. The second one you requested is completely covered by the first and I do not have a pdf of it. I do not have a pdf of the last reference, so I emailed a tif image file of each page. Let me know if you need anything more.

Just in...my email to you was not delivered. It was 3 MBytes in size. Is this too big? The error message I received (I put a * in place of the @ in your address) was:

Your message did not reach some or all of the intended recipients.

Subject: Requested papers from EDABoard
Sent: 11/23/2005 6:11 AM

The following recipient(s) could not be reached:

mipt*ngs.ru on 11/23/2005 6:12 AM
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< ms-smtp-02.nyroc.rr.com #5.0.0 SMTP; 591 your host [24.24.2.56] is blacklisted, see **broken link removed**. >

 

[cheng]

Hello. As far as the proper EM modeling of a complex circuit (as Lange coupler), it is more of an art than rule of thumb - Jim is just right here. We can't basically "define" rules of thumb - it largely depends on how good we are with the inherent discrepancy between model and real life on one hand and how bad the systems engineering guy is on the other.

My advise is to not get crazy about EM modeling - just be rational and use your EM knowledge most of the time. Whether thickness is important or not is best checked...by checking as Jim lso said - no receipe here I guess, and it is particularly true now, when any solver may yield thick vs. thin metal response of simple structures in seconds. For couplers one ought to look the capacitance per unit length and judge if varies a lot or not.
When you are happy with results and reached a point of convergence of the design just give it a try. Make the structure, test and analyze results. This will tell you alot about design flows if any (hopefully none) or will show if you are still in the spec or will give you a clue if something needs to be improved.
I've seen staff designing circuits on PC like hell and than boy...it is much different in reality because the measurement was not properly deembedded (for example).
Most of the parasitic effects (like metal thickness) has been dealt with analytically long ago - one may like resorting to seminal works of S. Cohn(before the big clog of the "green" magazine)) and others to see what physical effects are there to be and then attempt to quantify it by EM solver. Bond wires in Lange coupler is varying a lot and it strongly depends on the skills of the technician - both the length and the shape of the bond may be crtical.
Like I said, measurements may be different for many reasons and one should not get confused when his coupler is not exactly what expected. I'd start looking the coupling first and then probably the impedance mismatch for it may be well impaired in the measurement process, but it largely depends on your needs and application.
As for couplers, I've seen cases where the edge taper had pronounced effect and yet it was difficult to simulate by any EM solver.


Regards,

 

[Dillon]

I have the document about lange couper.
but I can't update it .

 

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