EBG structure modeling in CST

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shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

10 Jul 2007 10:43 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

Joined: 06 Feb 2007
Posts: 182
Helped: 4
Location: WhiteHouse

06 Nov 2008 17:15 EBG structure modeling in CST

anyone try to simulate this ones?

piboo

Joined: 06 Feb 2008
Posts: 84
Helped: 2

07 Nov 2008 12:33 EBG structure modeling in CST

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

Joined: 29 Jul 2006
Posts: 328
Helped: 28

11 Nov 2008 15:16 Re: EBG structure modeling in CST

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

Joined: 12 Nov 2007
Posts: 23

26 Nov 2008 16:08 Re: EBG structure modeling in CST

shahid78 wrote:

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

Joined: 29 Jul 2006
Posts: 328
Helped: 28

26 Nov 2008 18:04 Re: EBG structure modeling in CST

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

Joined: 06 Oct 2006
Posts: 18

01 Dec 2008 9:05 Re: EBG structure modeling in CST

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

piboo

Joined: 06 Feb 2008
Posts: 84
Helped: 2

01 Dec 2008 10:48 EBG structure modeling in CST

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

Last edited by piboo on 01 Dec 2008 19:34; edited 1 time in total

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

01 Dec 2008 14:40 Re: EBG structure modeling in CST

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

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01 Dec 2008 14:40 Ads

piboo

Joined: 06 Feb 2008
Posts: 84
Helped: 2

01 Dec 2008 19:38 EBG structure modeling in CST

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 :p Wink

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

01 Dec 2008 20:28 Re: EBG structure modeling in CST

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

Joined: 06 Feb 2008
Posts: 84
Helped: 2

03 Dec 2008 12:15 EBG structure modeling in CST

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

Joined: 29 Jul 2006
Posts: 328
Helped: 28

04 Dec 2008 0:45 Re: EBG structure modeling in CST

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

Joined: 06 Feb 2007
Posts: 182
Helped: 4
Location: WhiteHouse

19 Jan 2009 15:40 EBG structure modeling in CST

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

Joined: 06 Feb 2008
Posts: 84
Helped: 2

20 Jan 2009 20:44 EBG structure modeling in CST

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 Smile

regards

piboo

si14

Joined: 27 Sep 2006
Posts: 1061
Helped: 664
Location: North America

15 Feb 2009 12:48 EBG structure modeling in CST

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

Joined: 26 Mar 2008
Posts: 153
Helped: 10
Location: UK

22 Feb 2009 8:49 EBG structure modeling in CST

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

piboo

Joined: 06 Feb 2008
Posts: 84
Helped: 2

23 Feb 2009 11:18 EBG structure modeling in CST

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

Joined: 26 Mar 2008
Posts: 153
Helped: 10
Location: UK

24 Feb 2009 0:56 EBG structure modeling in CST

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

Joined: 06 Feb 2008
Posts: 84
Helped: 2

24 Feb 2009 10:16 EBG structure modeling in CST

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

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

24 Feb 2009 13:48 Re: EBG structure modeling in CST

hi all

yes i agree with piboo. i have seen some articles which model microstrip line over EBG structure to characterize the surface wave bandgap of EBGs,

Prafuldeo can you post your model land s21 result so we can use whether you are making any mistake in modeling or suggest something else to resolve your problem

regards
shahid

prafuldeo

Joined: 26 Mar 2008
Posts: 153
Helped: 10
Location: UK

25 Feb 2009 20:07 Re: EBG structure modeling in CST

Hello piboo and shahid.
Thank you for replying my query. I've attached my cst model which is the same as Samii's Microstrip antenna with EBG paper. I've modelled 8x5 EBG with 50 ohm microstrip line over it. But with this method I can't match the results with paper results. Atleast I should be getting the same band-gap as in paper. I've also attached the result page from paper. Also in the same paper samii did his simulations using infinitesimal dipole source with ebg in between. Can we do same in CST?? Please let me know how to obtain the correct results using CST. Thanks and Regards.

Praful

Sorry, but you need login in to view this attachment

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

26 Feb 2009 14:18 Re: EBG structure modeling in CST

hi prafuldeo

i am not able to open your model. which version of CST you are using?

can you try to send the model again

regads

piboo

Joined: 06 Feb 2008
Posts: 84
Helped: 2

27 Feb 2009 9:57 EBG structure modeling in CST

hi shahid

to open the prafuldeo's project:
1/ open the project --> bugg
2/ insert variable p, g and h
3/ Open and update the history list

Then it will work

regards

Piboo

prafuldeo

Joined: 26 Mar 2008
Posts: 153
Helped: 10
Location: UK

27 Feb 2009 12:29 EBG structure modeling in CST

Hello Shahid.
I've used CST 2009 for this project. Please let me know if you can't open the project.

Regards
Praful

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

28 Feb 2009 14:01 Re: EBG structure modeling in CST

hi prafuldeo

well i am still not able to open the project

i tried defining the variables p,g and h and then tried to update the history list

but it says variable values are too small.

so what values should i use for p, g and h?

regards

note: also i cant see this model of micro strip line over EBG structure in the Samii paper which you mentioned in your post?
so can you tell me to which paper results you are comparing to ur results?
also how u decided about the microstrip line width ? it should be 50 ohm line for matching with wave port. so which thickness and Er u used for calculating the microstrip line width for 50 ohm characteristic impedance?

prafuldeo

Joined: 26 Mar 2008
Posts: 153
Helped: 10
Location: UK

28 Feb 2009 20:56 EBG structure modeling in CST

Hello Shahid..
Thanks for reply. The paper i m trying to simulate is Fan Yang and Yahya Rahmat-Samii, “Microstrip Antennas Integrated with Electromagnetic Band-Gap (EBG) Structures: A Low Mutual Coupling Design for Array" . The model I've uploaded is the simple EBG design based on paper. I want the band-gap for that but using finite EBG structure say 6x6 cells . The periodic boundary conditions method simulates the infinite EGB but its no good for real conditions. The microstrip I used is 50 ohm matched. But results I got is not matching the published results. So if you have simulated this paper please let me know. Also I'll upload CST 2008 model for the same so that you can open it.

Regards
Praful

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

01 Mar 2009 19:00 Re: EBG structure modeling in CST

hi prafuldeo

well thats why i asked you in my last post. i can t see any model in your refered paper which is simulating microstrip line over EBG structure.

the figure which you mentioned is for infinitisimal diple surrounded by finite EBG cells.

so how can you get the comparable result for your model and this paper model?

can you explain?

also i asked you how u model 50 ohm microstrip line?
i can't get 50 ohm for your modeled line. thats why i asked you which thickness and permitivity value u choose for calculating the width of the line

i hope now u understand whay i am asking

regards

prafuldeo

Joined: 26 Mar 2008
Posts: 153
Helped: 10
Location: UK

08 Apr 2009 8:45 EBG structure modeling in CST

Hello Shahid,
I'll try to explain my query here. I've posted new thread " EBG surface wave characterisation using Samii setup in CST " please have a look at that also .

Now for complete EBG characterization we need two results (1) Reflection phase (2) Surface wave band-gap. methods of finding reflection phase ( macro method & wave guide method) is discussed in many places in this forum and there is no confusion associated with that . Now I am looking for the best possible method (in terms of accuracy) for obtaining surface wave band-gap. There are many setups to do that. One is as you said Full or terminated 50ohm microstrip line. But it gives the filter characteristics of the EBG and I am interested in the surface wave attenuation of EBG.
Second method is to model one column of EBG and put waveguide ports on both ends and make boundaries periodic to mimic a semi-infinite EBG and measure the S21 to get the band-gap. Now this method is close but it doesn't give band-gap information for finite EBG, say 6x6. The tird alternative is using samii set up which uses the infinitesimal dipole source and reference plane on the edges. For antenna purposes I think this one gives most accurate results as it gives the band-gap results depending on number of EBG rows. So I was wondering is it possible to simulate same setup in CST?? Because if we can generate the same results in CST then we'll know that other EBG's which we'll design is giving correct results and it saves the time and effort of fabrication and measurement. I've uploaded samii model in my new thread.
Have a look and give some thought about it.

Thanks & Regards

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

08 Apr 2009 12:33 Re: EBG structure modeling in CST

Hello prafuldeo

well i appreciate your detailed explanation on EBG characterization. i try to answer some of ur queries.

well i think surface wave characterization using 50 ohm microstrip line is the best for finding surface wave bandgap of finite EBG structures . i dont know why you are saying its giving filter characteristics of EBG and not surface wave bandgap.

in my view there is not much difference between the two. after all bandgap means filtering of waves and by looking at S21 u find the waves that have been filtered by EBG.

regarding the Samii setup , yes i am also interested to model the same setup in CST.
i was looking at your model. i dont understand why you have used wave guide port at the edge?

becoz in this way you are exciting two ports , the discrete port and waveguide port which i think u dont want. correct me if i am wrong.

i will also try to think and model the same setup in CST. and let you know if i get convincing results and i hope u will do at ur end and share your observation.
however , i think u need to use probes to capture the electric field at the edges for the all the frequency range. but in Samii paper they have plotted E². so u need to do some processing in excel to get the same results.
i hope u will succed in getting good results.
hope to be in contact with u on this topic

cheers
shahid