[SI-LIST] Re: TEM wave propagation and standing waves
- From: Ankit wangoo <ankit.wangoo@xxxxxxxxx>
- To: Davi Correia <davi.correia@xxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Mon, 4 Mar 2013 08:39:26 +0530
Hi Davi
I understand these boundary conditions.From this we get result that standing
wave in transmission line which
is terminated by short,We find that current (magnetic field ) and Voltage
(electric field) are actually completely out of phase. when current is
max, voltage is zero and vice-versa.
but how this concept get into concept we discussed about TEM wave
propagation where E and H are in phase?Is it not necessary for TEM wave to
have E and H to be in phase?
regards
Ankit
On Mon, Mar 4, 2013 at 1:59 AM, Davi Correia <davi.correia@xxxxxxxxx> wrote:
> Hello Ankit,
> When you terminate your TL by a short (in EM theory they call it
> "perfectly electric conductor"- PEC), your tangential electric field has to
> be zero. The only way for that to happen is if your incident wave has a
> value of, say, +a, your reflected wave has to have -a (the tangential
> component). That way, at your short (PEC) you have a minimum (zero). That
> is not true for the magnetic component. As a matter of fact, the short is
> where you magnetic field (tangential) is maximum. Hence, they have to be
> completely out of phase. The same argument is true if you terminate your TL
> with a (perfect) open, but this time you flip who is zero and who is max.
>
> If you want, you can also see this from a circuit point of view: if you
> terminate with a short, you can not have any voltage, right? That is
> electric field. But the current will be very large (maximum, in fact). That
> is magnetic field. And if it is open, there is no current (zero magnetic
> field) but large voltage (electric field).
>
> If you want more info, any undergrad level EM book should have this (Ramo,
> Shadiku, Pozar, etc.).
>
> I hope it helps.
>
> Regards,
> Davi
>
>
>
> ------------------------------
> *From:* Ankit wangoo <ankit.wangoo@xxxxxxxxx>
> *To:* si-list@xxxxxxxxxxxxx
> *Sent:* Sunday, March 3, 2013 8:16 PM
> *Subject:* [SI-LIST] TEM wave propagation and standing waves
>
> Hi
> We all know in transmission line structures such as co-axial
> cables, strip-line and micro strip-lines(partially ,if we assume field
> lines remains inside the dielectric) , electromagnetic energy flows in TEM
> mode, that is electric and magnetic field are always perpendicular to each
> other.
> We also know that characteristics of TEM waves guided by transmission lines
> are same as those for uniform plan wave propagating in an unbound
> dielectric medium.
> When we solve Helmholtz equation we find that Electric field can have one
> of solution as E=a*e^j(wt-kz) + b*e^j(wt+kz). where first term is a forward
> travelling wave and send is backward travelling wave.
> From Ampere circuital law in point form , we can find that H,
> jw*mu**H*=del
> cross *E* . Then H some out to be in phase with E field .That means that at
>
> a particular position and at particular time when electric field
> is maximum , magnetic field will also be maximum.
>
> however , when we study standing wave in transmission line which
> is terminated by short.We find that current (magnetic field ) and Voltage
> (electric field) are actually completely out of phase. when current is
> max, voltage is zero and vice-versa
>
> What can explain this difference in analysis ?
>
>
> I was thinking more about this,,, standing waves are formed by two waves
> and each of them electric field and magnetic field are in phase.however in
> standing wave , because of reflection one of them get polarized in
> different direction such that some points electric field gets cancelled and
> some point magnetic field get cancelled.
>
> however ,i am not completely convinced.Can somebody shed some light on this
> or refer me to some appropriate reading material?
>
> Thanks for your help
> Ankit wangoo
>
>
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