[SI-LIST] Re: HFSS solution issue


Hi, Arun,

I cannot agree with your estimation:
IL=3D20log10(1-0.005) and RL=3D20log10(0.005)

Notice the dB does not linearly depend on the absolute value. According to
the help in HFSS, the max delta S refers to the absolute diffference between
two iterations. You are trying to see how much will be the variations on S
in dB. Simple derivation gives the max variation:

delta S in dB <= 20log10(|S|+|deltaS|)-20log10(|S|)=20log10(e)x|deltaS/S|

Provided |deltaS/S| << 1.  So it depends on the value of S too. For example,
deltaS=0.005, S=0.05, then S in dB = -26dB, deltaS  in dB = 0.87 dB. The
relative error is about 3.4%. 

Regards,

Mick





-----Original Message-----
From: Chandrasekhar Arun [mailto:achandra@xxxxxxx]
Sent: Friday, January 24, 2003 5:46 AM
To: Dan_Swanson@xxxxxxxxxxxx; mike_bihan@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: HFSS solution issue



Hello Dan and all HFSS users,
        Excellent comments from Dan and it really summarises what every HFSS
=
new user needs to know reg. solving his/her model. A few points from my =
experience
1. My primary application with HFSS is solving chip-package =
interconnects and I use a delta-S of 0.005. This number is not =
sacrosanct, but when coverted to dB is -0.043 dB for insertion loss and =
-46 dB for return loss
IL=3D20log10(1-0.005) and RL=3D20log10(0.005)
The key is finding an optimum between solution accuracy and time. I =
expect my structures to have an insertion loss of about 1 dB at 5 GHz =
and it is Ok for me if my HFSS results are 1.043 or 0.957 dB. However if =
you are trying to extract the S-parameters of a low-loss short line, =
maybe this error is too high. However, already to achieve 0.005 eroor I =
have to live with about 25000 tetrahedra and this takes a few hours to =
simulate for 20 points and there is no way I can think of delta-S lower =
than 0.005!
2. If you are usinh HFSS at low frequencies, remembet to Solve Inside =
Metals !
3. To compare your results with VNA measurements always de-embed and =
re-normalise with 50 ohms

one question
does anyone know how you can manipulate the amount of memory used by =
HFSS while solving in the RAM and the disk? I have 1GB of RAM, still =
HFSS always swaps some data with the disk. I remember that the deafult =
is 70% RAm and 30% dis, but I do not see this always!
Regards
 =20
Arun Chandrasekhar
PhD Student: RF Packaging     =09
IMEC | MCP/MaRS Group =09
Phone:  +32 16 28 82 28 =09
Fax:    +32 16 28 10 97 =09
Email:  achandra@xxxxxxx <mailto:achandra@xxxxxxx>  =09
Seeds for Tomorrow's World <http://www.imec.be/>  =09
 =20
IMEC, Kapeldreef 75, 3001 Leuven, Belgium   |  Phone:+32 16 28 12 11  =
Fax:+32 16 22 94 00  |   Website: www.imec.be <http://www.imec.be/>=20



This e-mail and/or its attachments may contain confidential information. =
 It is intended solely for the intended addressee(s).
Any use of the information contained herein by other persons is =
prohibited.  IMEC vzw does not accept any liability for the contents of =
this e-mail and/or its attachments.=20


-----Original Message-----
From: Swanson, Dan [mailto:Dan_Swanson@xxxxxxxxxxxx]
Sent: Thursday, January 23, 2003 17:23
To: 'mike_bihan@xxxxxxxxxxxx'; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: HFSS solution issue




Bi, Han

I think you are a little confused on how the solution setup goes.

Adaptive Single Frequency can be run by itself or it
is the starting point for a Frequency Sweep.

So you adapt the mesh at some frequency, typically the highest
freq you are interested in. Then you start the frequency sweep
using that adapted mesh. So the mesh is "overkill" for the low
freqs and just right for the high freqs. Knowing this, if you
are trying to cover many octaves in frequency, then maybe
several runs using different adapt freqs is more efficient.

So in the setup menu you select both the Single Freq Adapt
and the Freq Sweep you want at the same time. The software then
does both.

If you run a Discreet Sweep, results should be fine. A Fast Sweep
tries to derive the result from the minimum number of discreet=3D20
freq solutions. Watch out for the both ends of the sweep range
and always check the results at least once with a discreet sweep.
If you ask for a very wide Fast Sweep range, the software often
suggests that you break it up into smaller segments.

As to number of adapts, that is very tricky. Basically you need
to identify the key parameter in your analysis and figure out
what it takes to get there. For example, I do a lot of resonators.
So I look at convergence of resonant frequency as function of meshing
parameters. Remember this is very general purpose software, you always
know more about you particular problem than the developer or the =3D
software.
You have to use that knowledge to guide the software to the right
solution.

Using the default settings, the starting mesh in HFSS is very coarse.
I typically set LAMBDA_REFINE_TARGET (system variable) to .02 or .033
Refinement percentage to 40% (default is 20%).  And maybe run 5 to 10
adapts. I set Delta-S limit to 1e-6, Delta-S achieved is very problem
dependent and does not always imply absolute convergence. Of course
you are looking for a convergence curve that is a nice smooth =3D
parabolla.

The geometrical resolution in your model will also affect convergence.
I tend to draw cylinders, etc kind of coarse, 8 or 12 sides to a =3D
cylinder.
I do this to speed things up. But sometimes if you make things too =3D
coarse
the convergence curve will oscillate, or you may converge to the wrong
final value. For example, look at impedance of a coax line as a =3D
function
of how many segments you use to define the cylinders.

All this is in my new book, coming out in May 2003:

http://www.artechhouse.com/default.asp?Frame=3D3DBook.asp&Book=3D3D1-5805=
3-3=3D
08-6&Cou
ntry=3D3DUS&Continent=3D3DNO&State=3D3DMA


Best regards,


Dan

Dan Swanson                     EMAIL:  d.swanson@xxxxxxxx
Forem USA                               PHONE:          978-834-4085
37 South Hunt Road              FAX:    978-388-7077
Amesbury, MA  01913


> -----Original Message-----
> From: Bi Han [mailto:mike_bihan@xxxxxxxxxxxx]
> Sent: Thursday, January 23, 2003 10:52 AM
> To: List` Si
> Subject: [SI-LIST] HFSS solution issue
>=3D20
>=3D20
>=3D20
> hi, ansoft guies:
>=3D20
> There is one simple question about HFSS.
>=3D20
> Since Adaptive 'Single frequency' analysis will allow users=3D20
> to setup 'Requested Passes', what number will be suitable? I used 7.
>=3D20
> However, issues come up!
> The results,obtained by 'Single Frequency', differs greatly=3D20
> from 'Sweep' analysis=3D20
>=3D20
> results? Because of the higher accuracy of 'Single frequency'=3D20
> analysis, I prefer it than sweep one. (Actually,sweep results=3D20
> is the Pass 1 results on Single Frequency analysis.)
>=3D20
> Then, what value does 'sweep' analysis have, with so poor=3D20
> accuracy, whose mesh will not be refined. In another way, in=3D20
> which way should we treat the data from 'sweep analysis'?
>=3D20
> Sincerely,
> Bi, Han
> Sjtu, EMLAB
>=3D20
>=3D20
>=3D20
> ---------------------------------
> Do You Yahoo!?
> =3D
"=3DBF=3DEE=3DBF=3DEE=3DB8=3DDF=3DB9=3DF3=3DB5=3DE4=3DD1=3DC5=3DA3=3DAC=3D=
B5=3DE3=3DBB=3DF7=3DB2=3DCE=3DBC=3DD3=3DC6=3DFB=3D
=3DB3=3DB5=3DB5=3DF7=3DB2=3DE9!"
>=3D20
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