# help simulate EBG structure with periodic boundary in CST

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#### meerek

##### Newbie level 5
Hello !!

I work with CST not long, and I need simulate one cell of EBG mushroom structure with periodic boundary conditions...Trouble is, that a donˇt know, whicht feed or port I must use ( I think PLANE WAVE) and how I must setting solve for results S11 and phase.

Meerek

#### maxkun

##### Newbie level 3
Re: help simulate EBG structure with periodic boundary in CS

meerek said:
Hello !!

I work with CST not long, and I need simulate one cell of EBG mushroom structure with periodic boundary conditions...Trouble is, that a donˇt know, whicht feed or port I must use ( I think PLANE WAVE) and how I must setting solve for results S11 and phase.

Meerek

I think this may help
Good luck

#### prafuldeo

##### Full Member level 3
hi meerek,
make a one unit cell of your EBG and make boundary conditions for X as electric and Y as magnetic. Define port at some distance from top of unit cell and deembed it to the top of the unit cell. Then make both Z min and Z max as electric. simulate for your frequency range in transient solver. In arg of s-parameters u should get the phase diagram.

Regards

#### maxkun

##### Newbie level 3
Re: help simulate EBG structure with periodic boundary in CS

prafuldeo said:
hi meerek,
make a one unit cell of your EBG and make boundary conditions for X as electric and Y as magnetic. Define port at some distance from top of unit cell and deembed it to the top of the unit cell. Then make both Z min and Z max as electric. simulate for your frequency range in transient solver. In arg of s-parameters u should get the phase diagram.

Regards

I have some questions.
1 does this method really work? have you compared it with measurement?
2 why do you choose electric and magnetic boundaried for the side wall of the unit cell ? cause i see somewhere else periodic boundaries are used.

#### abdoeng

##### Advanced Member level 2
hi,if u confuse with that method that i already test it with (CST and HFSS) give good comparison
that method has limited to only normal incident,so if u like check any oblique angle,sorry u that method not work well
so i suggest u use floquet mode that allow ur changing the angle of incident ,in CST in frequency solver
in HFSS ,it already supported,i upload artical in HFSS,just look for it here in that site
i check the two method(CST and HFSS) with floquet method,very good result happened
regards

### meerek

Points: 2

#### meerek

##### Newbie level 5
Re: help simulate EBG structure with periodic boundary in CS

Thanks all for answer.

I have new problem. I have finite ebg model of structure and I need simulate this structure without dipele antenna. I tried solve this model with open boundary conditions and two ports on top and bottom of boundary condition. But results in transient solver are not good.

#### shahid78

##### Full Member level 5
Re: help simulate EBG structure with periodic boundary in CS

hi

if you post your model than people will be able to give you more helpful advice on what you want to achieve and what you are getting.

thanks

#### prafuldeo

##### Full Member level 3
Hi Meerek,
I suppose you want to determine the band-gap of the finite EBG structure. That can be done by microstrip method. But I am also not able to get 100% consistent results. Other method is to simulate semi-infinite EBG and measure the s21 between two ports. I am still looking for perfect solution and will share if get any new information.

Regards

#### shahid78

##### Full Member level 5
Re: help simulate EBG structure with periodic boundary in CS

hi prafuldeo

you mention to use Electric boundary condition for Zmin and Zmax for unit cell modeling?

i think we should be using open boundary conditions,

can you explain a bit?

also i remember once u mentioned you are working on tutorial for characterizing EBG structures using CST.
have u managed to complete it?

regards
shahid

#### meerek

##### Newbie level 5
Re: help simulate EBG structure with periodic boundary in CS

Hello

here is screen of my model, EBG structure without printed dipole. Structure is consist of 8 x 6 unit cell. Supposed resonant frekvency is on cca 2,5 GHz. Which method of solve is better to use?

thanks

#### abdoeng

##### Advanced Member level 2
friend.we need ur CST model,not foto as we could help

Added after 2 minutes:

but from the foto,there are some errors
1-u just use one EBG cell
using E walls that bounded the polarized electric field of waveguide port
3-use the opposite walls of h walls
upper wall free space
lower as infite ground
see s11 argument
hintort must be embedded to the ground plane

#### meerek

##### Newbie level 5
Re: help simulate EBG structure with periodic boundary in CS

Hi abdoeng

I would like to send you my model, but I don´t know which file is enough for start this. Thanks for answer, I tried simulate one unit cell but with periodic boundary conditions(results too no good). I will try to use your settings of boundary, but I am not sure, if it´s case for periodic structure....

#### prafuldeo

##### Full Member level 3
Hello Shahid,
I was mentioning about the waveguide method as its much quicker than macro method for evaluating reflection phase. And yes Zmax will be open. But I am still not able to find the satisfactory results for surface wave band-gap for finite EBG's. I am working on it and I've posted the model used by Fan Yang and samii in new thread but I need to find out how to provide small dipole source for it...

#### anil_21p

##### Member level 1
If you are taking FDTD solver ...use Plan wave as source . You can control direction by theta and phi values

#### abdoeng

##### Advanced Member level 2
to share anil_21p,try to use floquet mode in CST with more easy for determination (theta and phi)

#### meerek

##### Newbie level 5
Re: help simulate EBG structure with periodic boundary in CS

Hi,

what macro method for transient periodic boundary do you mean?, I didn´t found anything (I have CST MW 2006), hm I ·am not at wits' end, I tried unit cell walls method, periodic walls method with wavegate port, but I don´t know, results are bad...!

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