[SI-LIST] Re: (no subject)
- From: "Tabatchnick, Justin" <justin.tabatchnick@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 10 Dec 2002 15:55:29 -0800
Hi all;
I have to jump in to add my 2 cents for all it's worth. First of all the =
realative dielectric constant is not frequency dependent - you can =
explain light dispersion not by a variation of dielectic with frequency =
but a variation of speed in the medium with the relative dielectric =
constant . Velocity =3D frequency times wavelength , wavelength is equal =
to the wavelength divided by the square root of the relative dielectric =
constant- white light is made up of a spectrum of varying wavelengths =
all traveling at the same speed in air however in a medium their speeds =
differ and that is why you see a seperation. the only way you will see a =
variation in the dielectric constant is in a non-homogenous medium. On =
the other hand if a medium has any conductivity to it you will see a =
variation with the loss tangent with frequency.
Regards
Justin
-----Original Message-----
From: Loyer, Jeff [mailto:jeff.loyer@xxxxxxxxx]
Sent: Tuesday, December 10, 2002 12:25 PM
To: Jian X. Zheng
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: (no subject)
Thanks for the information. I'm still a bit confused. For further =3D
clarification:
In your first point, you imply that, for a homogenous medium, dispersion =
=3D
is not possible (and Pozar implies this same thing for a TEM plane wave =
=3D
on page 170 of his book). Is that correct? =3D20
I thought Er could vary with F. For instance, in optics, v =3D3D c/n, =
=3D
where v is the phase velocity of a wave, c is the speed of light in a =
=3D
vacuum, and n is the refractive index of the material. For light, this =
=3D
refractive index is a function of frequency (hence prisms work). If Er =
=3D
varied with F, wouldn't you get dispersion?
What am I missing?
Jeff Loyer
-----Original Message-----
From: Jian X. Zheng [mailto:jian@xxxxxxxxxx]
Sent: Tuesday, December 10, 2002 10:44 AM
To: Loyer, Jeff; lifehappiest@xxxxxxxxxxx; steven.corey@xxxxxxxxxxxxxx;
si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: (no subject)
Hi:
I would like to give a few comments on dispersion:
1. For TEM mode, the wave is propagating in one single medium. If the
permittivity (Er) and the permeability (Mur) are constants, the phase
velocity will be the same at each frequency and it is not a dispersive
system. Coaxial and striplines are such cases if we neglect the loss on =
=3D
the
metallics bounding it.
2. For non-TEM wave, the wave is propagating in more than one medium. On =
=3D
a
typical microstrip or multiple layer structures, the wave can not =3D
propagate
in the horizontal direction (a). If it propagates in horizontal =3D
direction,
the phase of the wave can not match on the surface of the air and the
substrate because the wave propagates at different velocity in the air =
=3D
and
the substrate. The mechanism is much more complicated. However, to =3D
simplify
it for illustration, you can imagine the wave will be bouncing back and
forth inside the substrate between the ground plane and the =3D
air-substrate
surface. The direction of the power transportation is still along the
micrstrip in the horizontal direction. However, it is the final effect =
=3D
of
the bouncing back and forth. At a specific frequency, the angle of the =
=3D
wave
will be fixed in order to form a waveguide mode. Also, the angle of the =
=3D
wave
will be changing with frequency. Therefore, the phase velocity at each
frequency will be different even though the Er and Mur are the same.
(a)
air
---> ----
substrate
------------
ground
(b)
air
--------------------------
substrate, \/\/
--------------------------
grouund plane
3. I saw comments that dispersion is related to loss. This is really not
necessary. For a rectangular waveguide (RWG), theoretically, we can use =
=3D
PEC
to build the rectangular tube. There is no loss involved. However, a RWG =
=3D
is
always dispersive. That is due to the bouncing back and forth angle of =
=3D
the
wave inside the waveguide. RWG is the best example to illustrate how the
wave is propagating inside a dispersive TLN. The wave has to form an =3D
angle
to form a mode in order to propagate in the RWG. It is the same for
microstrip. Those TLNs with one single medium and more than 1 conductor =
=3D
are
exception. Thanks!
Best regards,
-----------------------------------------------------------------------
Jian-X. Zheng, Ph.D
Zeland Software, Inc., 48890 Milmont Drive, 105D, Fremont, CA 94538, =3D
U.S.A.
Tel: 510-623-7162, Fax: 510-623-7135, Web: http://www.zeland.com
---------------------------------------------------------------------
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Loyer, Jeff
> Sent: Tuesday, December 10, 2002 9:55 AM
> To: lifehappiest@xxxxxxxxxxx; steven.corey@xxxxxxxxxxxxxx;
> si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: (no subject)
>
>
>
> I've been trying to better understand dispersion and its effects on =
=3D
=3D3D
> signal integrity. Allow me to state what I believe, and feel free to =
=3D
=3D3D
> correct any falacies I've developed (or clarify what I've stated).
>
> 1) The key factor "creating" dispersion is the fact that, for a given =
=3D
=3D3D
> medium, different frequencies will travel at different velocities. =
=3D
=3D3D
> I.E., the Er for a material varies, depending on frequency. This same =
=3D
=3D3D
> effect is responsible for prisms' breaking light into its constituent =
=3D
=3D3D
> components and, interestingly enough, causes distortion of earthquake =
=3D
=3D3D
> waves as they travel through the earth.
>
> 2) I've heard the term associated with microstrip, but don't know why =
=3D
it =3D3D
> couldn't be present in stripline.
>
> 3) The net effect on our (digital S.I. types) signals of interest =3D
would =3D3D
> be that a pulse would appear rounded after passing through a =3D
dispersive =3D3D
> medium.
>
> 3) I don't think Hspice can simulate this phenomena, and I don't know =
=3D
if =3D3D
> ADS can, either.
>
> 4) The way I would expect to measure the effect would be with a VNA - =
=3D
I =3D3D
> would expect my S21 phase rate-of-change to vary with frequency. =3D
I.E., =3D3D
> for a non-dispersive medium, S21 phase appears as a regular sawtooth. =
=3D
=3D3D
> For a dispersive medium, I would expect the period of that sawtooth to =
=3D
=3D3D
> vary with frequency (probably very linearly). I haven't measured the =
=3D
=3D3D
> effect this way (that I know of, it might have been too subtle for me =
=3D
to =3D3D
> notice), nor have I seen data demonstrating the effect.
>
> I would love clarification on the terms "medium dispersion" vs. "wave =
=3D
=3D3D
> dispersion" vs "phase dispersion". I thought there was only a single =
=3D
=3D3D
> dispersion effect of phase velocities being different for different =
=3D
=3D3D
> frequencies.
>
> Thanks for your insights...
>
> Jeff Loyer
>
>
> -----Original Message-----
> From: Xin Wu [mailto:lifehappiest@xxxxxxxxxxx]
> Sent: Tuesday, December 10, 2002 6:54 AM
> To: steven.corey@xxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: (no subject)
>
>
>
> Steve, it is not a good idea to mix things together. Wave =3D
dispersion=3D3D20
> definitely has nothing to do with loss, conceptually. Dispersion is =
=3D
=3D3D
> related=3D3D20
> to phase velocity, but the loss is related to energy. Of cause, =3D
because=3D3D20
> signal pulse consists of a bunch of frequency components, =3D
different=3D3D20
> components propagate at different speed, this makes the pulse shape =
=3D
=3D3D
> change=3D3D20
> at the reception. However, the total energy of the pulse won't =
be=3D3D20
> dissipated. Dispersion of medium is another concept. If we talking =3D
about =3D3D
> a=3D3D20
> dispersive medium, this means that the dielectric constant of the =3D
medium =3D3D
> is=3D3D20
> frequency dependent, the medium is dispersive. Kramer Kronig =3D3D
> relationship is=3D3D20
> to explain the medium dispersion rather than wave dispersion.
> Of cause, when the medium is frequency dependent, both wave dispersion =
=3D
=3D3D
> and=3D3D20
> signal loss will be happening.
>
>
>
>
>
> Xin Wu
> Ph.D student,
> University of Maryland, College Park
> Http://www.wam.umd.edu/~xwu
>
>
>
>
>
>
> >From: Steve Corey <steven.corey@xxxxxxxxxxxxxx>
> >Reply-To: steven.corey@xxxxxxxxxxxxxx
> >To: si-list@xxxxxxxxxxxxx
> >Subject: [SI-LIST] Re: (no subject)
> >Date: Mon, 09 Dec 2002 16:44:28 -0800
> >
> >
> >This illustrates an interesting point, which is that if you have
> >dispersion, then you have to have frequency-dependent losses as well.
> >The Kramers-Kronig relationship (a.k.a. causality) states that the =
=3D
real
> >part and the imaginary parts of the dielectric constant are tightly
> >related to each other. As a result, frequency-dependent phase =3D
velocity
> >is always accompanied by frequency-dependent attenuation, and vice
> >versa. So you can easily make the argument that describing something =
=3D
=3D3D
> as
> >"dispersive" is the same as describing it as "lossy".
> >
> >Yu Liu wrote:
> >
> > > Jeff,
> > >
> > > By definition, I think dispersive effect is the frequency-related =
=3D
=3D3D
> effect
> > > (phase velocities at different spectrums). However, since the =
=3D
=3D3D
> losses
> > > are also frequency-dependent, sometimes people just use the term
> > > interchangbly, which causes confusions. Distinguish the two terms
> > > (dispersive and loss) would make things clearer.
> > >
> > > Yu
> > > =3D3D3D=3D3D3D=3D3D3D
> > >
> > > Loyer, Jeff wrote:
> > >
> > >
> > >>Yu,
> > >>When you use the term "dispersive", are you talking about =3D
losses=3D3D20
> >(resistive, skin effect, dielectric), or about differences in =3D
phase=3D3D20
> >velocities (page 170 of Pozar's book)? I've heard others refer to =
=3D
loss =3D3D
>
> >effects as dispersive and have had confusion as a result. Are both =
=3D
=3D3D
> uses of=3D3D20
> >the term "dispersive" correct?
> > >>
> > >>Jeff Loyer
> > >>
> > >>
> > >>-----Original Message-----
> > >>From: Yu Liu [mailto:yu_liu@xxxxxxxxxxxxx]
> > >>Sent: Friday, December 06, 2002 9:32 PM
> > >>To: xlzhou@xxxxxxxxx
> > >>Cc: 'Xin Wu'; si-list@xxxxxxxxxxxxx
> > >>Subject: [SI-LIST] Re: (no subject)
> > >>
> > >>
> > >>
> > >>Mick,
> > >>
> > >>To answer your question: In theory, Yes. In practice, No.
> > >>
> > >>The fundamental principle for SPICE model approach is using lumped
> > >>elements (RLC) to model distributed effect (S-parameter). For =3D
lower
> > >>frequency and small size, it is possible. But for broad-band =3D3D
> frequency
> > >>and large size (say, 20' FR-4), it is very hard to model the =3D3D
> dispersive
> > >>effects accurately. That's why people start to use =3D3D
> frequency-dependent
> > >>elements, or better yet, import S-parameter directly into Spice =
=3D
=3D3D
> engine.
> > >>
> > >>
> > >>Regards,
> > >>
> > >>Yu
> > >>=3D3D3D=3D3D3D=3D3D3D
> > >>
> > >>Apache Design Solutions
> > >>web: www.apache-da.com
> > >>
> > >>
> > >>
> > >>Zhou, Xingling (Mick) wrote:
> > >>
> > >>
> > >>
> > >>>Xin Wu
> > >>>
> > >>>Thanks for your information. It will be valuable.
> > >>>However, it still contains something like (from the example on =
=3D
the =3D3D
> web=3D3D20
> >you
> > >>>referred)
> > >>>
> > >>>E11 11 12 FREQ {V(10,5)}=3D3D3D
> > >>>
> > >>>which will not be accepted by some circuit simulators such as =3D
ADS. =3D3D
> It=3D3D20
> >is
> > >>>similar to Ansoft fullwave SPICE. I know HSPICE and PSPICE can =
=3D
=3D3D
> handle=3D3D20
> >it.
> > >>>
> > >>>Although it is still a research topic in terms of efficiency, =
=3D3D
> stability=3D3D20
> >and
> > >>>accuracy etc., I know the problem [S] ---> SPICE model (reduced =
=3D
=3D3D
> models)=3D3D20
> >is
> > >>>solvable without the following limitations in several ways. But, =
=3D
=3D3D
> can we
> > >>>generate broadband SPICE models without frequency dependent =3D
lookup=3D3D20
> >tables
> > >>>such as " FREQ " ? Or is it still solvable without components =
=3D
=3D3D
> "FREQ"=3D3D20
> >etc. ?
> > >>>
> > >>>Regards,
> > >>>
> > >>>Mick
> > >>>
> > >>>-----Original Message-----
> > >>>From: Xin Wu [mailto:lifehappiest@xxxxxxxxxxx]
> > >>>Sent: Friday, December 06, 2002 8:38 PM
> > >>>To: scott@xxxxxxxxxxxxx; xlzhou@xxxxxxxxx
> > >>>Cc: si-list@xxxxxxxxxxxxx
> > >>>Subject: Re: [SI-LIST] Re: (no subject)
> > >>>
> > >>>
> > >>>Hi, XL,
> > >>> If you want to convert S-matrix into a spice simulator, a lot =
=3D
of
> > >>>commercial software can do that--that's the simplest way. =3D
However, =3D3D
> it=3D3D20
> >is
> > >>>possible for yourself to make a equivalent subcircuit which can =
=3D
=3D3D
> include=3D3D20
> >the
> > >>>timing and frequency info and then import to a spice like =3D3D
> simulator.=3D3D20
> >Here
> > >>>are some application notes:
> > >>>http://wwwinfo.cern.ch/ce/ae/Maxwell/apps/2stripem/2stripem.html
> > >>>If you want to get involved in more details, I remembered that =
=3D
=3D3D
> somebody=3D3D20
> >did
> > >>>his Ph.D work on this in UIUC around early 1990s'.
> > >>>
> > >>>
> > >>>
> > >>>Xin Wu
> > >>>Ph.D student,
> > >>>University of Maryland, College Park
> > >>>Http://www.wam.umd.edu/~xwu
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>>From: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
> > >>>>Reply-To: scott@xxxxxxxxxxxxx
> > >>>>To: xlzhou@xxxxxxxxx
> > >>>>CC: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
> > >>>>Subject: [SI-LIST] Re: (no subject)
> > >>>>Date: Fri, 06 Dec 2002 13:45:41 -0800
> > >>>>
> > >>>>
> > >>>>Mick,
> > >>>>
> > >>>>There are two solutions which I use:
> > >>>>
> > >>>>1) Apache Nspice is an Hspice compatabible simulator that can
> > >>>>co-simulate with Touchstone S-parameter files.
> > >>>>http://www.apache-da.com/
> > >>>>
> > >>>>2) Sigrity BroadBand Spice can convert Touchstone s-parameter =
=3D
=3D3D
> files=3D3D20
> >into
> > >>>>spice black boxes.
> > >>>>http://www.sigrity.com/
> > >>>>
> > >>>>Both are scary accurate in both the frequency and time domain.
> > >>>>
> > >>>>regards,
> > >>>>
> > >>>>scott
> > >>>>
> > >>>>--
> > >>>>Scott McMorrow
> > >>>>Teraspeed Consulting Group LLC
> > >>>>2926 SE Yamhill St.
> > >>>>Portland, OR 97214
> > >>>>(503) 239-5536
> > >>>>http://www.teraspeed.com
> > >>>>
> > >>>>
> > >>>>Zhou, Xingling (Mick) wrote:
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>>>Hello,
> > >>>>>
> > >>>>>Did anybody successfully generate broadband (DC-20GHz) SPICE =
=3D
=3D3D
> model=3D3D20
> >from S
> > >>>>>matrix for complex structures using the SPICE generator in ADS =
=3D
? =3D3D
> Or=3D3D20
> >any
> > >>>>>other alternatives. I know Ansoft fullwave SPICE does the work.
> > >>>>>Unfortunately, some circuit simulators do not support the =3D3D
> frequency
> > >>>>>dependent lookup table sources. We can definitely use [S] =3D3D
> directly,=3D3D20
> >but
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>some
> > >>>>
> > >>>>
> > >>>>
> > >>>>>users still prefer SPICE models. Any experience to share ?
> > >>>>>
> > >>>>>Thanks,
> > >>>>>
> > >>>>>Xingling(Mick) Zhou, PhD
> > >>>>>Signal Integrity Technologist
> > >>>>>Agere Systems
> > >>>>>
> > >>>>>Tel: 610-712-7462
> > >>>>>Fax: 610-712-4081
> > >>>>>
> > =3D3D
> =3D
>>>>>------------------------------------------------------------------
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=3D
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> > >>>_________________________________________________________________
> > >>>Add photos to your messages with MSN 8. Get 2 months FREE*.
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> > =3D
>>>------------------------------------------------------------------
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> > >
> > >
> >
> >
> >--
> >-------------------------------------------
> >Steven D. Corey, Ph.D.
> >Time Domain Analysis Systems, Inc.
> >"The Interconnect Modeling Company."
> >http://www.tdasystems.com
> >
> >email: steven.corey@xxxxxxxxxxxxxx
> >phone: (503) 246-2272
> >fax: (503) 246-2282
> >-------------------------------------------
> >
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>
>
> _________________________________________________________________
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http://groups.yahoo.com/group/si-list/messages=20
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
=20
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List archives are viewable at:
//www.freelists.org/archives/si-list
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Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
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