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# reflection phase diagram of ebg/pbg surface using CST

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#### shahid78

##### Full Member level 5
ebg pbg

i am trying to find the bandgap of ebg structure using reflection phase diagram method. i am using CST MWS 2006B.

i model the unit cell of the ebg strucuture and then illuminate it with the plane wave and set up the probe to record the phase of the reflecing singal.

but i cant get the expected result. can any body tell me whether this method is correct and if correct what mistake i am making and if someboday know what other method i can use to find the bandgap of PBG/EBG structure using CST.

#### iaia

##### Member level 2
pbg phase diagram

shahid78 said:
i am trying to find the bandgap of ebg structure using reflection phase diagram method. i am using CST MWS 2006B.

i model the unit cell of the ebg strucuture and then illuminate it with the plane wave and set up the probe to record the phase of the reflecing singal.

but i cant get the expected result. can any body tell me whether this method is correct and if correct what mistake i am making and if someboday know what other method i can use to find the bandgap of PBG/EBG structure using CST.

Hi, have you solved your problem? I'm trying to simulate the phase of the reflection coefficient but I have some problems with the boundary conditions. Can you help me?
[/quote]

Manju Abraham

### Manju Abraham

Points: 2

#### shahid78

##### Full Member level 5
cst pbg unit cell

hi

well you have to model 3 structures .

1 PEC model
2 vaccum model
3 actual model

and then use macro to find the reflection phase diagram.
can you explain a bit what boundary problem you are talking about,

regards

#### iaia

##### Member level 2
Hi,
I have posted my CST file yesterday. I have a unit cell (a square mushroom-type geometry) and I have selected periodic boundary for xmin, xmax, ymin, ymax, open boundary for zmax and Et=0 for zmin. I have used the plane wave excitation, but in this way the phase of the reflection coefficient does not appear in the results. So I used a waveguide port , but the resulting phase has a strange behavior (with a discontinuity roughly corresponding to the resonance frequency instead of crossing for 0°). This is the first time I use CST, but I did not have any problems with doing the same simulation in Designer.
Thanks a lot.

#### shahid78

##### Full Member level 5
well i dont think u can use waveguide port with periodic boundary conditions.
so i think you should use plane wave exciation for periodic boundary condition in x and y direction and Et=0 at Zmin and open at Zmax.

and then you can use macro to find the reflection phase diagram

regards

#### abdoeng

hi iaia,i already simulate mushroom using cst
what is ur request
send email to me,ok
regards

Points: 2

### ahmedgh

Points: 2

#### sassyboy

##### Full Member level 1
Make sure that you use the "Unit Cell" boundary condition instead of the "Periodic" boundary condition.

In the pre-2006 version, yes, we used macros, but this is no longer necessary in 2006B, it is also straightforward too. What you have to do is to have an additional model of just the PEC groundplane with a thickness equal to that of the overall thickness of the EBG structure. In the end you are left with two phase plots, one corresponds to EBG and the other corresponds to a referece PEC slab. Use excel and carry out a phase comparison and the result is the reflection phase.

#### shahid78

##### Full Member level 5
hi sassyboy

the method which you are talking seems to be interesting.
can you please tell which port you are using with unit cell boundary condition
or you are just using plane wave excitation

thanks

#### iaia

##### Member level 2
Hi all,

this is my cst file. I have set the boundary conditions as above and used a plane wave excitation, but when i tried to use the macro for the S parameters I got an error: "array lower bound is larger than upper bound".

Ps: I am using CST 5.0.1, but I'll get CST 2006b within few days.

thanks

#### abdoeng

hi all,i try to simulate ebg model using ansoft designer and cst with the above technique of sassayboy
the results so ggod in both cases
i use cst 2006b,avoiding using periodic walls,plane wave and macro files
regards

#### iaia

##### Member level 2
Hi abdoeng,
I'm still having problems with my simulations in cst, can you tell me the details of your model?
Thanks a lot

#### abdoeng

hi iaia,sorry for my lating reply aas u email me
1-i build my model normaly,ok,
2-then use electric walls in -x,+x
3-biulding magnetic walls in -y,+y
use waveguide port in top of structure
(use embedded port from waveguide port to the upper point in mu structure)ok
then see argument of s paprameters
that all
u ask why e walls in -x,+x as to guide the electric filed that is polarized in x direction as u know

i hope it help

here my model

mehr65

### mehr65

Points: 2

#### iaia

##### Member level 2
Hi abdoeng,
it works!!! Just an other question (so far ): with this setup can I simulate a oblique incident plane wave?
Regards

#### shahid78

##### Full Member level 5
thanks abdoeng for your explanation of the problem.

however your method is a little different then sassyboy.

you are constructing only the actual model and then observing the argument of s parameters whereas sassyboy is constructing 2 models one the actual model and another PEC model with the same overall thickness. and then sassyboy is exporting the data of the 2 models and compare in excel to find reflection phase.

so i am confused which method is accurate yours or sassyboy.

any comments on this would clarify my doubts

thanks

#### abdoeng

akhy shahid,the method i test is correct that i compare that result with ansoft designer
so u can test them if u not sure my result is correct
regards
iaia,that method,i don't test it for any oblique angle,i so sorry,could u try it,i easy can do that but in ansoft designer,not in cst
regards

#### iaia

##### Member level 2
Hi abdoeng,
Ok, I will try.
I have seen some other posts where you talk of dispersion diagram. Have you already tried to get it for the mushroom-type structures? Can you please send me some examples? It would be of great help for me.
Thanks a lot

#### vulehuy93

##### Newbie level 2
Hi all,
I'm using CST2006. Which macro do I have to use to calculate the phase of reflection
coefficent?
This is the first time I use CST.
Regards

#### prafuldeo

##### Full Member level 3
Hi vulehuy93,
Go to the link below and you will get the ppt name PBG_Reflection_method. Download it and run the macros. Everything is explained in that macro.

Hope it helps.
Regards
Praful

#### vulehuy93

##### Newbie level 2
After unzip file reflection_macro, I have file reflection-method.bas
I copy it to make a macro in CST.
But when I use it for 3_hexa_structure_pec_01, the result is strange
My screen when I use macro

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