[SI-LIST] Re: (no subject)
- From: "Jian X. Zheng" <jian@xxxxxxxxxx>
- To: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- Date: Tue, 10 Dec 2002 14:39:57 -0800
Hi, Jeff:
For a single medium, dispersion is still possible if the Er is frequency
dependent. However, for most cases, Er has little dependency on the
frequency. That is why we can consider stripline is non-dispersive. For
microstrip circuits, the Ereff is more dependent upon frequency even when Er
is a constant of frequency due to the change of wave incident angle with
frequency. The change of wave incident angle is more related to those
transverse dimensions. In order to form a mode, we much have the so-called
transverse resonance. When the physical transverse dimensions are fixed,
increasing the frequency means that the electrical length of the transverse
directions become larger. The wave incident angle (theta) will change. When
the wave incident angle changes, the propagation constant in along the TLN
is kt=k*sin(theta) is no longer linearly dependent upon the frequency.
k=omega*sqrt(Er*Mur). As you can see, if Er*Mur is frequency independent, k
is linearly dependent upon the frequency and the phase velocity is unchanged
with frequency. However, kt=k*sin(theta) is no longer linearly dependent
upon the frequency because sin(theta) is changing with frequency. Normally,
the frequency dependency on (Er*Mur) is much less than the frequency
dependency upon sin(theta).
-------------dielectric surface----------------------
/|\ /
/ | \ /
/ | \ /
/ | \--direction of the back and forth waves.
/ | \ /
/ |theta\/
-----------------ground-------------------------
Thanks!
-----------------------------------------------------------------------
Jian-X. Zheng, Ph.D
Zeland Software, Inc., 48890 Milmont Drive, 105D, Fremont, CA 94538, U.S.A.
Tel: 510-623-7162, Fax: 510-623-7135, Web: http://www.zeland.com
---------------------------------------------------------------------
> -----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: RE: [SI-LIST] Re: (no subject)
>
>
> Thanks for the information. I'm still a bit confused. For
> further clarification:
>
> In your first point, you imply that, for a homogenous medium,
> dispersion is not possible (and Pozar implies this same thing for
> a TEM plane wave on page 170 of his book). Is that correct?
>
> I thought Er could vary with F. For instance, in optics, v =
> c/n, where v is the phase velocity of a wave, c is the speed of
> light in a vacuum, and n is the refractive index of the material.
> For light, this refractive index is a function of frequency
> (hence prisms work). If Er 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 the
> metallics bounding it.
>
> 2. For non-TEM wave, the wave is propagating in more than one medium. On a
> typical microstrip or multiple layer structures, the wave can not
> propagate
> in the horizontal direction (a). If it propagates in horizontal 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 and
> the substrate. The mechanism is much more complicated. However,
> to simplify
> it for illustration, you can imagine the wave will be bouncing back and
> forth inside the substrate between the ground plane and the air-substrate
> surface. The direction of the power transportation is still along the
> micrstrip in the horizontal direction. However, it is the final effect of
> the bouncing back and forth. At a specific frequency, the angle
> of the wave
> will be fixed in order to form a waveguide mode. Also, the angle
> of the 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 PEC
> to build the rectangular tube. There is no loss involved.
> However, a RWG is
> always dispersive. That is due to the bouncing back and forth angle of 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 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 are
> exception. Thanks!
>
> Best regards,
>
> -----------------------------------------------------------------------
> Jian-X. Zheng, Ph.D
> Zeland Software, Inc., 48890 Milmont Drive, 105D, Fremont, CA
> 94538, 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 =
> > signal integrity. Allow me to state what I believe, and feel free to =
> > 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 =
> > medium, different frequencies will travel at different velocities. =
> > I.E., the Er for a material varies, depending on frequency. This same =
> > effect is responsible for prisms' breaking light into its constituent =
> > components and, interestingly enough, causes distortion of earthquake =
> > waves as they travel through the earth.
> >
> > 2) I've heard the term associated with microstrip, but don't
> know why it =
> > couldn't be present in stripline.
> >
> > 3) The net effect on our (digital S.I. types) signals of
> interest would =
> > be that a pulse would appear rounded after passing through a
> dispersive =
> > medium.
> >
> > 3) I don't think Hspice can simulate this phenomena, and I
> don't know if =
> > ADS can, either.
> >
> > 4) The way I would expect to measure the effect would be with a
> VNA - I =
> > would expect my S21 phase rate-of-change to vary with
> frequency. I.E., =
> > for a non-dispersive medium, S21 phase appears as a regular sawtooth. =
> > For a dispersive medium, I would expect the period of that sawtooth to =
> > vary with frequency (probably very linearly). I haven't measured the =
> > effect this way (that I know of, it might have been too subtle
> for me to =
> > notice), nor have I seen data demonstrating the effect.
> >
> > I would love clarification on the terms "medium dispersion" vs. "wave =
> > dispersion" vs "phase dispersion". I thought there was only a single =
> > dispersion effect of phase velocities being different for different =
> > 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 dispersion=20
> > definitely has nothing to do with loss, conceptually. Dispersion is =
> > related=20
> > to phase velocity, but the loss is related to energy. Of cause,
> because=20
> > signal pulse consists of a bunch of frequency components, different=20
> > components propagate at different speed, this makes the pulse shape =
> > change=20
> > at the reception. However, the total energy of the pulse won't be=20
> > dissipated. Dispersion of medium is another concept. If we
> talking about =
> > a=20
> > dispersive medium, this means that the dielectric constant of
> the medium =
> > is=20
> > frequency dependent, the medium is dispersive. Kramer Kronig =
> > relationship is=20
> > to explain the medium dispersion rather than wave dispersion.
> > Of cause, when the medium is frequency dependent, both wave dispersion =
> > and=20
> > 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 real
> > >part and the imaginary parts of the dielectric constant are tightly
> > >related to each other. As a result, frequency-dependent phase velocity
> > >is always accompanied by frequency-dependent attenuation, and vice
> > >versa. So you can easily make the argument that describing something =
> > as
> > >"dispersive" is the same as describing it as "lossy".
> > >
> > >Yu Liu wrote:
> > >
> > > > Jeff,
> > > >
> > > > By definition, I think dispersive effect is the frequency-related =
> > effect
> > > > (phase velocities at different spectrums). However, since the =
> > 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
> > > > =3D=3D=3D
> > > >
> > > > Loyer, Jeff wrote:
> > > >
> > > >
> > > >>Yu,
> > > >>When you use the term "dispersive", are you talking about losses=20
> > >(resistive, skin effect, dielectric), or about differences in phase=20
> > >velocities (page 170 of Pozar's book)? I've heard others
> refer to loss =
> >
> > >effects as dispersive and have had confusion as a result. Are both =
> > uses of=20
> > >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 lower
> > > >>frequency and small size, it is possible. But for broad-band =
> > frequency
> > > >>and large size (say, 20' FR-4), it is very hard to model the =
> > dispersive
> > > >>effects accurately. That's why people start to use =
> > frequency-dependent
> > > >>elements, or better yet, import S-parameter directly into Spice =
> > engine.
> > > >>
> > > >>
> > > >>Regards,
> > > >>
> > > >>Yu
> > > >>=3D=3D=3D
> > > >>
> > > >>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 the =
> > web=20
> > >you
> > > >>>referred)
> > > >>>
> > > >>>E11 11 12 FREQ {V(10,5)}=3D
> > > >>>
> > > >>>which will not be accepted by some circuit simulators such
> as ADS. =
> > It=20
> > >is
> > > >>>similar to Ansoft fullwave SPICE. I know HSPICE and PSPICE can =
> > handle=20
> > >it.
> > > >>>
> > > >>>Although it is still a research topic in terms of efficiency, =
> > stability=20
> > >and
> > > >>>accuracy etc., I know the problem [S] ---> SPICE model (reduced =
> > models)=20
> > >is
> > > >>>solvable without the following limitations in several ways. But, =
> > can we
> > > >>>generate broadband SPICE models without frequency
> dependent lookup=20
> > >tables
> > > >>>such as " FREQ " ? Or is it still solvable without components =
> > "FREQ"=20
> > >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 of
> > > >>>commercial software can do that--that's the simplest way.
> However, =
> > it=20
> > >is
> > > >>>possible for yourself to make a equivalent subcircuit which can =
> > include=20
> > >the
> > > >>>timing and frequency info and then import to a spice like =
> > simulator.=20
> > >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 =
> > somebody=20
> > >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 =
> > files=20
> > >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 =
> > model=20
> > >from S
> > > >>>>>matrix for complex structures using the SPICE generator
> in ADS ? =
> > Or=20
> > >any
> > > >>>>>other alternatives. I know Ansoft fullwave SPICE does the work.
> > > >>>>>Unfortunately, some circuit simulators do not support the =
> > frequency
> > > >>>>>dependent lookup table sources. We can definitely use [S] =
> > directly,=20
> > >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
> > > >>>>>
> > > =
> > >>>>>------------------------------------------------------------------
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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
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> > >fax: (503) 246-2282
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