[SI-LIST] Re: Transmission Line Causality
- From: agathon <hreidmarkailen@xxxxxxxxx>
- To: steven.d.corey@xxxxxxxxxxxxxx
- Date: Thu, 5 Jul 2007 02:08:51 -0700
Steve,
"...the best solution is to use a field solver that produces causal results
..."
And therein lies the rub. I find the same observations as I've had about
the root problem, but if the permittivity input to the solver has no hope of
satisfying causality, how can the solver be expected to produce a causal
result? I'm restricting myself to stripline Tlines.
The real root problem seems to be unreal permittivity, due to lack of
ability or interest by dielectric manufacturers.
I'm interested in _exactly_ the veracity of my description and, if valid, is
the only way to find the complex Dk up to 30GHz something like using a VNA
to extract magnitude and phase and then fit to theory (for a stripline)?
Thanks for any help.
On 4/25/07, steven.d.corey@xxxxxxxxxxxxxx <steven.d.corey@xxxxxxxxxxxxxx>
wrote:
>
> In answer to the original poster, the best solution is to use a field
> solver that produces causal results -- at least within the requested
> frequency interval. It starts with the most complete information on the
> physical system, so it has the best chance of producing an accurate,
> causal model. Black-box post-processing does not have that luxury.
> There is a large class of functions that are causal, so you can't expect
> that blind post-processing will enforce causality by perturbing your
> data to more closely match the original system -- it may send it off in
> a different direction.
>
> Short of causal field solver results, there are various ways to match FD
> data to analytical functions, thereby enforcing time-domain causality.
> But again, such post processing steps operate with no knowledge of the
> physical system other than the RLGC parameters you have provided, so
> it's not fair to expect them to do the right thing.
>
> As Vladimir has pointed out, given your causal model parameters, you
> then need to make sure your simulator maps them to causal (and accurate)
> time-domain results, or your prior effort was wasted.
>
> There are number of errors that map strangely or can be implicitly
> introduced when converting measurement or field solver data from the FD
> to the TD for analysis, characterization and test. Non-causality is one
> the most obvious of these, so it can serve as a lower bound on the total
> error in the system.=20
>
> -- Steve
>
> ------------------------------------------------------------------------
> -
> Steven D. Corey, Ph.D.
> Principal Engineer
> Tektronix - Enabling Innovation
> =20
> http://www.tdasystems.com
> http://www.tektronix.com
> =20
> email: steven.corey@xxxxxxxxxxxxx
> phone: (503) 627-6816
> fax: (503) 627-2260
> ------------------------------------------------------------------------
>
>
>
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