EBG structure modeling in CST

[shahid78]

shahid

i am interested in finding the bandgap of ebg surface using CST.
i am confused how to find the reflection phase diagram or dispersion diagram for the EBG surface.
which solver should i use frequency domain . time domain or eigen mode solver?
also whether to use waveguide port or plane wave guide excitation?

can anyone post the example model of calculating the bandgap of PBG/EBG surface using CST. this will make things very easy to follow.


looking for any sort of help.

thanks
shahid

 

[cuongtran]

anyone try to simulate this ones?

 

[piboo]

hi

for phase reflexion you can use either time or frequency domain solver:

Two methods for each solver:
-time domain solver:
1/ using the macro with a plane wave
2/ using magnetic and electric boundaries conditions in order to have a TEM wave.

-frequency domain solver:
1/using unit cell and do a de-embedding
3/using magnetic and electric boundaries conditions in order to have a TEM wave.

For dispersion diagram you need to choose the eigenmode solver.

regards

piboo

 

[shahid78]

h piboo

how you were able to do de-embeding in unit cell template of frequency domain solver?
i will appreciate if you comment on this


regards

 

[dentai]

h piboo

how you were able to do de-embeding in unit cell template of frequency domain solver?
i will appreciate if you comment on this


regards

De-embedding means that you have to shift the waveport on the EBG plane to measure the reflection phase.

 

[shahid78]

hi dentai

yes are right about the definition of de embeding

we are discussing how we can do this using FD solver of CST MWS

i hope now you understand what we r looking for

regards

 

[qqqooo]

de embeding ,
If you have obtained S parameters, go to CST: Results>>S-parameter Calculations>> Deembed S parameter.

 

[piboo]

Hi all,

with Unit Cell you can't use the macro:
Results>>S-parameter Calculations>> Deembed S parameter

you have to do it by yourself with the template post processing:

The steps are these:
1/ Load the file corresponding to your simulate phase: normally it's pZmax(1)Zmax(1).sig
((Load 1D Result))

2/ You need to have a file which contains all the frequency points. For that Copy a *.sig file in your CST folder and rename it as Fband.sig (for example). Then In CST copy one of your result, for example, your phase result.
Open Fband.sig with excel, delete all and paste it.

EDIT: Then delete all data except the first colum (which contains frequency points).
Copy this colum and paste it in the second colum
--> So you will have two colums which the same frequency points

Save it and load it as an external file in the template post processing (Load 1D Result)

3/ Calculate the deembeding:
In the Mix 1D Results window, enther the equation:
-2*(2*180*A/0.3)*Deemb/1000

with A=Fband.sig
and Deemb is the distance between your port and the surface.
I tune the Deemb distance in the background properties: Upper Z Distance = Deemb =20mm (at least).

4/ Calculate the phase reflexion to the surface:
Open again a Mix 1D Results Window and type:
A-B
with A=pZmax(1)Zmax(1).sig
B=The name of the Mix 1D Results of (3/)

5/ You can wrap it with the Unwrap/Wrap of 1D phase...

I hope you will understand (sorry for my english)
I'm currently writing an application note for CST which recalls all methods to caracterize EBG structures.

Regards

piboo

 

[shahid78]

hi piboo

first of all thanks for your good post on deembeding process using unit cell template.
i hope people at CST can realize this and introduce a built in technique for deembeding just like for time domain solver

its good to hear that you are writing an application note on different methods to characterized EBG in CST as currently not enough information is available and whateever is there is scattered all over the place.

jut for my information are you going to discuss both reflection phase and surface wave suppression characterization of EBGs in your application note?

also when are you going to finish it and share it with people so that many people like me can benefit from your worthy work

regards

 

[piboo]

Thanks shahid78,

I forget something, but I correct it in the previous post (see the EDIT).

In the application, I will show how to calculate the reflection phase for several methos in TD and FD.
I correct also the macro for phase reflection (calculate for vaccuum structure, then pec structure and the real structure).

Maybe I will include dispersion diagram.
This application is nearly ready but in french, I have to translate it.
I think in January it will be finished.

regards

piboo

PS: If I helped someone... +1 for help will be nice

 

[shahid78]

dear piboo

first of all thanks for updating me on the application note you are working on.
other than dispersion diagram you can also add suspended microstrip line method to analyse surface wave suppression characteristics of EBG structures

also you mention u r writinng in french but its not a problem anyone can convert it to english. so you can post it once its complete and not worry about language

also some points which were not clear to me from your last post on de embeding method

3/ Calculate the deembeding:
In the Mix 1D Results window, enther the equation:
-2*(2*180*A/0.3)*Deemb/1000

with A=Fband.sig
and Deemb is the distance between your port and the surface.
I tune the Deemb distance in the background properties: Upper Z Distance = Deemb =20mm (at least).


can you let me know from where you get this equation (-2*(2*180*A/0.3)*Deemb/1000) or what is the theory behind this equation. also is there minus sign as well infront of this equation ?
also what do u mean by tune the deembed distance?

in my opinion this distance between port and surface is set in the beginning of simulation after that you cant change it after you simulation is finished .

looking forward to your comments

regards

 

[piboo]

Hi shahid

You'r welcome.

I don't use the microstrip line method because I don't know how does it works. If you have some references whose explains it, I would be enjoyed to take them.

For the equation of the deembeding:
The plane wave propagation can be write like (in vaccuum):

exp(-j*Beta*z)

where z is the direction of the wave's propagation

Beta=2*pi/lambda
--> (2*180*A/0.3)

So the phase can be write:
Phi=-Beta*Ddeemb

where Ddeemb (Ddeemb/1000 to have it in meter) is the distance between the source and the SHI surface.



The wave travel two times the distance Ddeemb (incident and reflected).
--> that's why there is a factor 2

When you use unit cell, you don't know the distance between source and the surface of the SHI.
By set a value in the upper Z distance you fix the box dimensions and also the origin of the source.

Hope everybody will understand,

regards

Piboo

 

[shahid78]

hi piboo

well thanks for your explanation of your deembeding equation but still some confusion.

why you need 2 columns of frequency points ?

regarding microstrip line method ,there is one paper on this topic but i am not able to find its full text .
but the idea is to model a 50 ohm microstrip line on the top of EBG structure. assign two ports at then end of this line and then analyse S21 to find the surface wave suppression bandgap

if you need any help on this you are most welcome . you can send me personal message

regards

 

[cuongtran]

Hi piboo,
Nice to hear that you will write out a help in CST + EBG, if it is possible please send me though in french,
Thanks you verymuch.

 

[piboo]

the report is soon finished ... be patient or if you need help ask don't hesitate to ask your questions I will try to answer to it


regards

piboo

 

[si14]

Good topic here. Thanks to friends.

BTW piboo,
any news from the report on EBG?
I am also interested in EBG and CST.

Thanks a lot.

 

[prafuldeo]

Hello friends ..
Any idea how to find S21 of EBG for both the TE and TM modes separetely??
Thanks & Regards
Praful

 

[piboo]

Hi all,

To masud: give me one more week, i'm a little bit busy in this moment, but if you have any questions we can try to resolve them.

To prafuldeo: I don't know what you'r looking for exactly ?

Do you want to see the S21 between an antenna and an EBG structure ?
Because the S21 corresponding to the port 1 is excited and you observe the transmission in the second port.
That's why I don't understand your questions because I don't see where are your ports.
Try to explain a little bit more your problem plz

regards

piboo

 

[prafuldeo]

Hi Piboo,
I've designed an EBG structure and now I want the S21 diagram for finding its surfacewave bandgap. There is no antenna, only two ports at corner of EBG. The S21 diagram I am getting is not correct. Any idea how to find surface wave band-gap for EBG??

Regards
Praful

 

[piboo]

Hi Prafuldeo,

Some papers used 2 microstrip line, one on each side of the ebg and they measure the transmission between them.

Other used a 50 Ohm microstrip line over the ebg and measure too the tansmission.

We have made some tests here and it's work.

What is exactly your problem ?

Can you post your result of your S21 diagram ?


regards

piboo