[SI-LIST] Re: HFSS S-parameters... issues?
- From: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>
- To: "George Peterson" <george_peterson@xxxxxxxxx>, "Scott McMorrow" <scott@xxxxxxxxxxxxx>
- Date: Thu, 10 Nov 2011 14:37:12 -0700
George,
Changing the radiation boundary size/type does effect results, and changing
the port size effects results. There are three types of radiation boundary,
and the port size effects the number of modes, wider lets in more lower
frequency modes. I go with their cononical port sizes for a baseline, and
select the appropriate boundary for the model I'm investigating. Search on
radiation boundary and port sizing in the index on the Help menu. Might be
a place to start. Did you put in integration lines on the ports? Other
than that...what The Scott said...with apologies to The Steve.
Ken
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of George Peterson
Sent: Thursday, November 10, 2011 12:11 PM
To: Scott McMorrow
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: HFSS S-parameters... issues?
Hi Scott,
I have not tried adjusting mesh parameters, or order of basis function, but
I'll give it a shot. For such a simple structure through only 10 GHz I
assumed that whatever defaults are present would suffice.
My Ansoft FAE reproduced the problem and his solution was to increase the
size of the surrounding airbox. This worked for me on microstrip lines but
appears to fall apart on stripline; that is, larger airboxes don't fix my
S11. I would hate to waste his time on a case of operator error if that's
what this is.
*Best Regards*,
George Peterson
Signal Integrity Engineer
Jabil Design Services
St. Petersburg, FL
On Thu, Nov 10, 2011 at 1:54 PM, Scott McMorrow <scott@xxxxxxxxxxxxx> wrote:
> George
>
> I've experienced no problems in HFSS V13.0.2 or with V14 beta. If the
> port impedance and the impedance of the structure are well-matched, you
> might be suffering from insufficient mesh on the transmission lines,
> because there are no reflections (and therefore only minute delta S
changes
> with meshing). I suggest that you speak with your Ansys application
> engineer about the problem you are having.
>
> best regards,
>
> Scott
>
> Scott McMorrow
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
> (401) 284-1827 Business
> (401) 284-1840 Fax
>
> http://www.teraspeed.com
>
> Teraspeed® is the registered service mark of
> Teraspeed Consulting Group LLC
>
>
> On 11/10/2011 1:31 PM, George Peterson wrote:
>
>> Good Day All,
>> Is anybody else noticing unexpected behavior of S-parameters (Touchstone
>> models) generated from transmission line structures in HFSS v13.0.2?
>>
>> I'm performing a linear port analysis in HSpice and when I use Touchstone
>> models generated from transmission lines in HFSS I get wacky results;
>> specifically, S11 magnitudes vary dramatically\unrealistically and
>> expected
>> resonances change frequencies or are missing altogether.
>>
>> When I take that same structure in HFSS and export a W-element model, the
>> HSpice results are as expected; for a 1 inch line, S11 peak ripples occur
>> at about -20 dB and, using lossless calculations as a rough guide, minima
>> match well at multiples of 1/2 lamdba (wavelength). I've also compared to
>> models generated in Polar and all transmission lines models exhibit
>> roughly
>> the same S11 behavior... except Touchstone from HFSS.
>>
>> Within HFSS, adjusting the size of the surrounding airbox, changing the
>> boundary conditions, adjusting the size of the waveports, and changing
the
>> technique for modeling dielectrics all effect the outcome that I'm seeing
>> but I have yet to see a lot of rhyme and reason.
>>
>> Can I get a sanity check please?
>>
>>
>> *Best Regards*,
>> George Peterson
>> Signal Integrity Engineer
>> Jabil Design Services
>> St. Petersburg, FL
>>
>>
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