[SI-LIST] Re: Propagation delay difference
- From: <steven.d.corey@xxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 15 Mar 2007 19:38:05 -0700
Hi Ihsan -- I would encourage you to look into one the various EM text
books. I did a quick survey of six different titles around the office,
and every one offers an analysis of TEM propagation in either coaxial
cable, stripline, or both.
-- 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
------------------------------------------------------------------------
-
=20
>-----Original Message-----
>From: Ihsan Erdin [mailto:erdinih@xxxxxxxxx]=20
>Sent: Thursday, March 15, 2007 4:49 PM
>To: Corey, Steven D
>Cc: si-list@xxxxxxxxxxxxx
>Subject: Re: [SI-LIST] Re: Propagation delay difference
>
>Hi Steven,
>
>There's no question the parallel plates of infinite extent will
>support the TEM mode of propagation. When you select a direction of
>propagation -say y-direction in a parallel plate system magnetic
>fields due to currents in the non-axial directions will cancel out
>owing to the symmetry and you'll be left with a net field in the
>transverse xz plane. But when the lateral symmetry is broken due to
>the finite size (like a stripline) so will be the TEM condition.
>
>Regards,
>
>Ihsan
>
>On 3/14/07, steven.d.corey@xxxxxxxxxxxxxx=20
><steven.d.corey@xxxxxxxxxxxxxx> wrote:
>> Hi Ihsan -- I haven't seen it stipulated before that=20
>conductors have to
>> have zero circumference in order for a system to support TEM
>> propagation. The infinite parallel-plate waveguide,=20
>analyzed in almost
>> every EM text, is a good example of a structure that supports TEM
>> propagation while not requiring conductors with zero cross section in
>> the transverse plane.
>>
>> The book I referenced earlier, "Analysis of Multiconductor=20
>Transmission
>> Lines" by Clayton R. Paul, has the relevant math for doing=20
>TEM analysis
>> where conductors have arbitrary cross-sectional shape in the=20
>transverse
>> plane. It includes stripline and coaxial cable examples,=20
>among others.
>>
>> The dimension that you do have to be aware of is the=20
>separation between
>> conductors in the transverse plane. If it is too large with=20
>respect to
>> your highest wavelength of interest, then higher order modes, if they
>> are excited, can propagate between the conductors. However, the
>> analysis of the TEM mode still stands, despite the potential=20
>presence of
>> these higher order modes.
>>
>> -- Steve
>>
>>=20
>---------------------------------------------------------------
>---------
>> -
>> Steven D. Corey, Ph.D.
>> Principal Engineer
>> Tektronix - Enabling Innovation
>> =3D20
>> http://www.tdasystems.com
>> http://www.tektronix.com
>> =3D20
>> email: steven.corey@xxxxxxxxxxxxx
>> phone: (503) 627-6816
>> fax: (503) 627-2260
>>=20
>---------------------------------------------------------------
>---------
>> -
>> =3D20
>>
>> >-----Original Message-----
>> >From: si-list-bounce@xxxxxxxxxxxxx=3D20
>> >[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Ihsan Erdin
>> >Sent: Wednesday, March 14, 2007 2:50 PM
>> >To: Ken Cantrell
>> >Cc: si-list@xxxxxxxxxxxxx
>> >Subject: [SI-LIST] Re: Propagation delay difference
>> >
>> >Ken,
>> >
>> >First, I have to make a correction to my earlier statement=20
>concerning
>> >the line width. A generic statement like "the finite size conductor
>> >circumference" is more appropriate. I think you'd agree that the
>> >fundamental assumption with the transmission line theory is the TEM
>> >mode of propagation along the axis of the (ideal) lines, which
>> >requires all the electric and magnetic field components to=20
>be confined
>> >to the transverse plane. In that case, all propagation=20
>modes will have
>> >the same velocity. In reality (PCB tracks, cable wires,=20
>etc.) however,
>> >the line circumference is not infinitely thin as the theory assumes.
>> >With this geometry you can't expect the current to be=20
>confined to the
>> >axis of the line. Any non-axial current component will give=20
>rise to an
>> >H-field which is not on the plane transverse to the direction of
>> >propagation any more. Now, we talk about a quasi-TEM mode of
>> >propagation which also applies to inhomogeneous media, lossy
>> >conductors, etc. Does this make sense?
>> >
>> >Regards,
>> >
>> >Ihsan
>> >
>> >On 3/14/07, Ken Cantrell <Ken.Cantrell@xxxxxxxxxxxxxxxx> wrote:
>> >> Ihsan -
>> >> Can you elaborate? I don't see how the width effects the=3D20
>> >mode velocities.
>> >> Thanks,
>> >> Ken
>> >>
>> >> -----Original Message-----
>> >> From: si-list-bounce@xxxxxxxxxxxxx
>> >> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Ihsan Erdin
>> >> Sent: Wednesday, March 14, 2007 9:41 AM
>> >> To: steven.d.corey@xxxxxxxxxxxxxx
>> >> Cc: si-list@xxxxxxxxxxxxx
>> >> Subject: [SI-LIST] Re: Propagation delay difference
>> >>
>> >>
>> >> Steven,
>> >>
>> >> A stripline structure doesn't support a pure TEM mode of=20
>propagation
>> >> even in a lossless homogeneous medium -owing to its=20
>width- hence the
>> >> difference in the mode velocities.
>> >>
>> >> Regards,
>> >>
>> >> Ihsan
>> >>
>> >> On 3/13/07, steven.d.corey@xxxxxxxxxxxxxx=3D20
>> ><steven.d.corey@xxxxxxxxxxxxxx>
>> >> wrote:
>> >> > Hi Ihsan -- all TEM waves propagate with the same velocity=3D20
>> >in a system
>> >> > of multiconductor transmission lines in a homogeneous medium, as
>> >> > determined by the properties of the medium. This is true=3D20
>> >for any number
>> >> > of coupled lines -- two coupled striplines is just a=20
>special case.
>> >> >
>> >> > This should make physical sense -- the velocity of a wave=3D20
>> >traveling in a
>> >> > homogeneous, linear, isotropic medium can not be changed=3D20
>> >by reorienting
>> >> > its fields. Since a TEM wave travels down a transmission=3D20
>> >line through
>> >> > such a medium with no obstructions, we should expect its=3D20
>> >velocity to be
>> >> > that of the dielectric medium. Reorienting its fields=20
>within the
>> >> > transverse plane, as we do by changing from even to odd=3D20
>> >excitation, or
>> >> > any combination of the two, will not change the velocity=3D20
>> >of propagation.
>> >> > You can find all the relevant mathematics in "Analysis of=3D20
>> >Multiconductor
>> >> > Transmission Lines" by Clayton R. Paul.
>> >> >
>> >> > Of course the ideal TEM case is never exactly realized=20
>in practice,
>> >> > since there are always some non-TEM effects -- conductor=3D20
>> >losses, finite
>> >> > lengths of the lines, lines turning corners, finite=20
>extent of the
>> >> > dielectric, the list goes on and on. But in pure theory,=3D20
>> >all of the
>> >> > modal velocities (if we even choose to call them separate=3D20
>> >modes) are
>> >> > identically equal.
>> >> >
>> >> > -- Steve
>> >> >
>> >> >=3D20
>> >---------------------------------------------------------------
>> >---------
>> >> > -
>> >> > Steven D. Corey, Ph.D.
>> >> > Principal Engineer
>> >> > Tektronix - Enabling Innovation
>> >> > =3D3D20
>> >> > http://www.tdasystems.com
>> >> > http://www.tektronix.com
>> >> > =3D3D20
>> >> > email: steven.corey@xxxxxxxxxxxxx
>> >> > phone: (503) 627-6816
>> >> > fax: (503) 627-2260
>> >> >=3D20
>> >---------------------------------------------------------------
>> >---------
>> >> > -
>> >> > =3D3D20
>> >> >
>> >> > >-----Original Message-----
>> >> > >From: si-list-bounce@xxxxxxxxxxxxx=3D3D20
>> >> > >[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Ihsan Erdin
>> >> > >Sent: Friday, March 09, 2007 3:50 AM
>> >> > >To: jbtera77@xxxxxxxxx
>> >> > >Cc: si-list@xxxxxxxxxxxxx
>> >> > >Subject: [SI-LIST] Re: Propagation delay difference
>> >> > >
>> >> > >Jongbae,
>> >> > >
>> >> > >Even in an homogeneous coupled stripline structure, the=3D20
>> >wave speed is
>> >> > >not the same for even and odd propagation modes, hence=3D20
>> >the difference
>> >> > >between common and diff. mode prop. delays. For cases=20
>where mutual
>> >> > >coupling is very small they get close but theoretically=3D20
>> >there'll be a
>> >> > >difference. The same reasoning applies to the coupled=20
>microstrip
>> >> > >lines.
>> >> > >
>> >> > >Regards
>> >> > >
>> >> > >Ihsan
>> >> > >
>> >> > >On 3/9/07, jbtera77@xxxxxxxxx <jbtera77@xxxxxxxxx> wrote:
>> >> > >> Hi, all
>> >> > >> As all know, in homogeneous strip line, the =
propagation=3D3D20
>> >> > >speed is the same
>> >> > >> for both differential and common mode.
>> >> > >>
>> >> > >> However, in inhomogeneous microstrip line, the=3D20
>> >propagation speed of
>> >> > >> differential mode is faster than that of common mode.
>> >> > >> In specific, the value of Cm/C is higher than Lm/L in=3D20
>> >inhomogeneous
>> >> > >> microstrip line while the values are same in=3D20
>> >homogeneous strip line?
>> >> > >>
>> >> > >> Could somebody let me know why it physically is?
>> >> > >>
>> >> > >>
>> >> > >> Thanks in advance,
>> >> > >> Jongbae Park.
>> >> > >>
>> >> > >>
>> >> > >>
>> >> > >> --
>> >> > >> =3D
>> --------------------------------------------------------Ph.D=3D3D20
>> >> > >Candidate
>> >> > >> StudentTerahertz Interconnection & Package=3D20
>> >Laboratory,Department of
>> >> > >> Electrical Engineering, Korea Advanced Institute of=20
>Science=3D3D20
>> >> > >and Technology
>> >> > >> (KAIST),373-1, Kusong-dong, Yusong-ku, Taejon 305-701,
>> >> > >>=3D3D20
>> >> > >KoreaFax)+82-42-869-8058Tel)+82-42-869-5458Mobile)+82-11-9787-7
>> >> > >966E-mail)
>> >> > >> pjb77@xxxxxxxxxxxxxxxxxxxxxx URL)
>> >> > >>=3D3D20
>> >> > >http://tera.kaist.ac.kr/---------------------------------------
>> >> > >-----------------
>> >> > >>
>> >> > >>
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