[SI-LIST] Re: Propagation delay difference
- From: "Ihsan Erdin" <erdinih@xxxxxxxxx>
- To: steven.d.corey@xxxxxxxxxxxxxx
- Date: Wed, 14 Mar 2007 10:41:01 -0500
Steven,
A stripline structure doesn't support a pure TEM mode of propagation
even in a lossless homogeneous medium -owing to its width- hence the
difference in the mode velocities.
Regards,
Ihsan
On 3/13/07, steven.d.corey@xxxxxxxxxxxxxx <steven.d.corey@xxxxxxxxxxxxxx> wrote:
> Hi Ihsan -- all TEM waves propagate with the same velocity in a system
> of multiconductor transmission lines in a homogeneous medium, as
> determined by the properties of the medium. This is true for any number
> of coupled lines -- two coupled striplines is just a special case.
>
> This should make physical sense -- the velocity of a wave traveling in a
> homogeneous, linear, isotropic medium can not be changed by reorienting
> its fields. Since a TEM wave travels down a transmission line through
> such a medium with no obstructions, we should expect its velocity to be
> that of the dielectric medium. Reorienting its fields within the
> transverse plane, as we do by changing from even to odd excitation, or
> any combination of the two, will not change the velocity of propagation.
> You can find all the relevant mathematics in "Analysis of Multiconductor
> Transmission Lines" by Clayton R. Paul.
>
> Of course the ideal TEM case is never exactly realized in practice,
> since there are always some non-TEM effects -- conductor losses, finite
> lengths of the lines, lines turning corners, finite extent of the
> dielectric, the list goes on and on. But in pure theory, all of the
> modal velocities (if we even choose to call them separate modes) are
> identically equal.
>
> -- Steve
>
> ------------------------------------------------------------------------
> -
> Steven D. Corey, Ph.D.
> Principal Engineer
> Tektronix - Enabling Innovation
> =20
> http://www.tdasystems.com
> http://www.tektronix.com
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>
> >-----Original Message-----
> >From: si-list-bounce@xxxxxxxxxxxxx=20
> >[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 wave speed is
> >not the same for even and odd propagation modes, hence the difference
> >between common and diff. mode prop. delays. For cases where mutual
> >coupling is very small they get close but theoretically there'll be a
> >difference. The same reasoning applies to the coupled microstrip
> >lines.
> >
> >Regards
> >
> >Ihsan
> >
> >On 3/9/07, jbtera77@xxxxxxxxx <jbtera77@xxxxxxxxx> wrote:
> >> Hi, all
> >> As all know, in homogeneous strip line, the propagation=20
> >speed is the same
> >> for both differential and common mode.
> >>
> >> However, in inhomogeneous microstrip line, the 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 inhomogeneous
> >> microstrip line while the values are same in homogeneous strip line?
> >>
> >> Could somebody let me know why it physically is?
> >>
> >>
> >> Thanks in advance,
> >> Jongbae Park.
> >>
> >>
> >>
> >> --
> >> --------------------------------------------------------Ph.D=20
> >Candidate
> >> StudentTerahertz Interconnection & Package Laboratory,Department of
> >> Electrical Engineering, Korea Advanced Institute of Science=20
> >and Technology
> >> (KAIST),373-1, Kusong-dong, Yusong-ku, Taejon 305-701,
> >>=20
> >KoreaFax)+82-42-869-8058Tel)+82-42-869-5458Mobile)+82-11-9787-7
> >966E-mail)
> >> pjb77@xxxxxxxxxxxxxxxxxxxxxx URL)
> >>=20
> >http://tera.kaist.ac.kr/---------------------------------------
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