how calculate propagation constant (beta) from FDTD

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red5000

Joined: 06 Nov 2006
Posts: 120
Helped: 32

28 Jun 2009 17:23 propagation constant

i need algorithme to calculate propagation constant (beta) from FDTD, and thanks.

iyami

Joined: 12 Apr 2008
Posts: 120
Helped: 16

29 Jun 2009 13:03 propagation constant beta

Have you made any progress since earlier this year?
Do you have a working FDTD program. If not that should be your first step.
Your question is too general it would help if you tell as more precisely what
your current status is and then we can proceed from there.

red5000

Joined: 06 Nov 2006
Posts: 120
Helped: 32

29 Jun 2009 22:20 calculate beta

i am a magister student, and i want to calculate the propagation constante from fdtd in a wave guide with a ferrite substarte, i have do an fdtd program to simulate the 3d wave filed in the wave guide, but i tray to obtain the propagation constant (beta) from this program with not success, i need any advice, even if the substrat is not in ferrite, and thanks.

iyami

Joined: 12 Apr 2008
Posts: 120
Helped: 16

30 Jun 2009 16:27 calculate phase of a wave beta

Quote:

if you tell as more precisely what your current status is

I meant with regards to the problem.

In any case: propagation constants describe how the amplitude of some wave changes over distance.
So you need to do/figure out the following

1) how is the wave defined (e.g. electric field amplitude in some mode, voltage wave, ....)

2) how do you measure it (if you use FDTD then you have to express the wave in terms of E/H fields)

3) measure at several distances

4) use some fitting method to determine the propagation constant.

red5000

Joined: 06 Nov 2006
Posts: 120
Helped: 32

30 Jun 2009 22:10 calculating propagation constant

thank you for your explain, and can you tell me about method to calculate the beta ?

Added after 1 hours 51 minutes:

and i have some difficulty to found documents, can you help me with any advice, and thanks

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iyami

Joined: 12 Apr 2008
Posts: 120
Helped: 16

01 Jul 2009 9:10 beta waveguide example

I don't mind helping if I can but can you tell me first what you know about steps 1-3.
The best way to compute beta (4 is one possibility) depends on those.

red5000

Joined: 06 Nov 2006
Posts: 120
Helped: 32

01 Jul 2009 17:17 how to get propagation constant in electric field

1) i am working in the gaussian pulse in a waveguide :
source = -2.0*((T-t0)./tw).*exp(-1.0*((T-t0)./tw).^2.0);

Ex(is,js,ks) = source(n);

2) in the loop i have use the maxwell equations of:
Ex(ii,jj,kk), Ey(ii,jj,kk), Ez(ii,jj,kk)
Hx(ii,jj,kk), Hy(ii,jj,kk), Hz(ii,jj,kk)

3) i have only plot the propagation of the wave in the waveguide, but i dont mesurig the amplitude

iyami

Joined: 12 Apr 2008
Posts: 120
Helped: 16

02 Jul 2009 0:15 wave propagation constant example

Quote:

1) how is the wave defined (e.g. electric field amplitude in some mode, voltage wave, ....)

2) how do you measure it (if you use FDTD then you have to express the wave in terms of E/H fields)

Quote:

I did not mean the FDTD definition.
There are many waves you could measure
- electric waves
- magnetic waves
- voltage waves
- power waves
...

Let us assume you mean electric waves (for example the average of the E fields in the waveguide
in the direction of propagation) then probably you want to measure beta for a/several
fixed frequency/ies.

Then the first thing is to measure the waves at different locations and then use FFT or DFT
to get the amplitude for this/these frequencies.

Then you have to find parameters a and b that exp((a+ib) * x) describes the amplitude and phase
of the waves at different distances x. Since that may not be possible you try to find a good
approximation using methods like curve fitting

red5000

Joined: 06 Nov 2006
Posts: 120
Helped: 32

02 Jul 2009 7:08 measure phase fdtd

- yes i am working on the electric field.
- and i must calculate the beta betwin 20 Ghz and 60 Ghz.
- i dont know how to measure the wave at different location and applicate the fft on it, and these location have the same disance betouin them ? and how to applicate the fft on them because the amplitudes is a constant and its not the same point to save historic of the field to calculate his fft ?
- and my program give a bad amplitude of E.
- and i belieave the fft is calculate at the same point and at different time of the field, not at at different place.

- i dont know the stage where i must calculate the the parameters a and b and how to calculate them, and how to use them to find beta ? and i dont know how to calculate the amplitude and phase of the wave ? and i must have a good approximation of what ?

-

- and if you want, i can send you my template program in your mail.

- i have a probleme with documentation, and my professor not have an idea in this method

iyami

Joined: 12 Apr 2008
Posts: 120
Helped: 16

02 Jul 2009 12:50 electric field propagation constant

Quote:

- yes i am working on the electric field.
- and i must calculate the beta betwin 20 Ghz and 60 Ghz.
- i dont know how to measure the wave at different location

it depends what you want to measure.
You should perhaps ask your professor what he wants
you to measure.

Quote:

and applicate the fft on it, and these location have the same disance betouin them ?

not necessarily

Quote:

and how to applicate the fft on them because the amplitudes is a constant and its not the same point to save historic of the field to calculate his fft ?
- and my program give a bad amplitude of E.

you have to record the field values at different locations for the whole simulation and then
compute the FFT for each location

Quote:

- and i belieave the fft is calculate at the same point and at different time of the field, not at at different place.

right but you have to do that for many different points: first you record a time signal, for example, the E field in the x-direction, at a fixed cell during the whole simulation, then you take the FFT.

If you do that at 5-20 cells along the waveguide you see that the further away you get from your sources the weaker the component for a fixed frequency gets. The propagation constant expresses
how much faster the signal gets weaker along the waveguide

Quote:

- i dont know the stage where i must calculate the the parameters a and b and how to calculate them, and how to use them to find beta ? and i dont know how to calculate the amplitude and phase of the wave ? and i must have a good approximation of what ?

That is the last (quite easy) step. Try to get the other ones correct first

Quote:

- and if you want, i can send you my template program in your mail.

I don't mind, but currently I have to write quite a bit of C and python code so I don't really
want to read any other languages right now. So we should leave it as a last resort

Quote:

- i have a probleme with documentation, and my professor not have an idea in this method

I think wikipedia is ok as a starting point

red5000

Joined: 06 Nov 2006
Posts: 120
Helped: 32

02 Jul 2009 17:37 electric field and propagation constant

thank you verry much my friend, if i progress, i contact you.

ksugahar

Joined: 08 Jun 2006
Posts: 14
Helped: 2

15 Jul 2009 21:33 propagation number beta electromagnetic

i am againt to computing a propagation constant with 3d solver. Most of the commertial solvers have a port solver which is a 2d em solver.

soufianisme

Joined: 13 May 2009
Posts: 9

31 Aug 2009 3:35 calculate constant beta

hello
may be i have the same problem; but my waveguide works between 8 and 12 GHz

the problems I found was due to

1-bad formulation of the ferrite modeling
2-the excitation form
3-the bad boundaries condition;at first the program work without ferrite; but when you introduce the ferrite code the fields go the infiny
4- ...

can you send me your code to revise it?
soufianisme at gmail dot com