<CST MWS> A periodic structure+Plane wave problems

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Pushhead

Joined: 19 Jan 2005
Posts: 195
Helped: 8

01 Sep 2005 14:37 cst network parameter extraction antenna

Hello all,

I'm simulating a periodic 2D planar structure. I am using a plane wave excitation to achieve the phase of the reflection coefficient.
As you'll see in the following pictures, I have used only one cell of the structure with periodic bundary conditions (sidewalls), Electric (bottom) and Open (initial wave-plane position). In addition i'm using several field-probes above the cell.

My main problem now is an unexplanable phase result (see picture). I get weird "jumps" of phase values. I understand that the angle is wrapped between -180 and 180 - but I cant explain that!

Why is this happening?
Do you have another idea of retrieving the phase of the ref. coeff. ?

Looking 4ward 2 your ideas and thoughts,
Tnx alot,
P.

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irfan1

Joined: 26 Oct 2003
Posts: 292
Helped: 15

01 Sep 2005 17:01 shahid

I guess you have to subtract the incoming field from the total scattered field. From the phase data, I can tell that what you observe is some sort of interference between the reflected signal and the incoming signal. There is a discussion on the forum about this issue .

sassyboy

Joined: 20 Sep 2003
Posts: 88
Helped: 14
Location: United Kingdom

01 Sep 2005 18:21 Re: <CST MWS> A periodic structure+Plane wave problems

Pushhead, irfan1 is right! The probes are measuring the interference between the incident and reflected signal. Moreover. this topic has been discussed before and was first initiated by irfan1 and the link is below. It should help.

h**p://www.edaboard.com/viewtopic.php?t=99578

Pushhead

Joined: 19 Jan 2005
Posts: 195
Helped: 8

04 Sep 2005 16:15 Re: <CST MWS> A periodic structure+Plane wave problems

Thanks alot!

I think it works (have'nt checked it thoroughly). I have built a (1)
PBG model+probe, (2) a vacuum model+probe and (3) a PEC model+probe.

I've calculated the following with complex field values:

a. E-reflected,pbg=E(1)-E(2);
b. E-reflected,pec=E(3)-E(2);
c. Ref. coeff. angle with respect to PEC=arg(E-reflected,pbg)-arg(E-reflected,pec).

I'm still having those weird "jumps", any idea ?

regards,
P.

eckypting

Joined: 02 Sep 2005
Posts: 44
Helped: 5
Location: Washington, DC

06 Sep 2005 20:20 Re: <CST MWS> A periodic structure+Plane wave problems

If you're only concerned with a normal incident plane wave, I would suggest using a waveguide port excitation instead of the plane wave excitation. Doing so will allow you to separate the incident and reflected fields, as well as deembed the port reference plane all the way to the surface of your structure so that you can observe the reflection phase for the EBG structure.

Cheers,
eckypting

irfan1

Joined: 26 Oct 2003
Posts: 292
Helped: 15

08 Sep 2005 18:24 Re: <CST MWS> A periodic structure+Plane wave problems

What would be the effect of using waveguide port along with the periodic boundary conditions on the plane of the waveguide? This seems a lot confusing and complicated to me. Any comments?

eckypting

Joined: 02 Sep 2005
Posts: 44
Helped: 5
Location: Washington, DC

09 Sep 2005 17:25 Re: <CST MWS> A periodic structure+Plane wave problems

irfan1 wrote:

What would be the effect of using waveguide port along with the periodic boundary conditions on the plane of the waveguide? This seems a lot confusing and complicated to me. Any comments?

Actually, the periodic boundary condition is not required for this type of problem if a waveguide port is used and all that is desired is the reflection phase at normal incidence... For a vertically polarized waveguide mode, the E-plane boundaries (i.e. top & bottom of the "waveguide") should be defined as PEC, and the H-plane boundaries (left & right sidewalls) as PMC. This will create a uniform, plane-polarized incident wave on a unit cell of the surface.

The advantage of the waveguide port is that it will automatically compute S-parameters and deembed to a user-defined reference plane (e.g. the top surface of the unit cell). This cannot be done with the plane wave excitation mode of analysis.

In the end, I would contend that this approach is much simpler and far less of a headache than the plane wave analysis approach. It doesn't require any sort of post processing - unless you consider de-embedding a post processing step...but that is relatively trivial to set up.

Cheers,
eckypting

irfan1

Joined: 26 Oct 2003
Posts: 292
Helped: 15

09 Sep 2005 19:51 Re: <CST MWS> A periodic structure+Plane wave problems

it is getting much clearer now. Still, I have the following question. Usually the lattice constant would be the half of the wavelength. This will restrict the dimensions of the waveguide port. Then one can not excite below a frequency range. Because one will hit the cutoff of the waveguide.Any solution?

eckypting

Joined: 02 Sep 2005
Posts: 44
Helped: 5
Location: Washington, DC

13 Sep 2005 23:03 Re: <CST MWS> A periodic structure+Plane wave problems

irfan1 wrote:

This is part of the reason for having the PMC (& not PEC) on the sidewalls, so that the waveguide appears as 2 parallel plates with no low-frequency cutoff...not to mention providing a uniform amplitude distrubution across the width of the cell. With PEC sidewalls, the waveguide will have a cutoff frequency, and the amplitude distribution will be sinusoidal.

Cheers,
eckypting

sergag

Joined: 29 Apr 2005
Posts: 35

20 Sep 2005 6:10 Re: <CST MWS> A periodic structure+Plane wave problems

Sorry - I new user in MWS... Where I can find a manual on MWS?

eckypting

Joined: 02 Sep 2005
Posts: 44
Helped: 5
Location: Washington, DC

20 Sep 2005 20:15 CST Microwave Studio Manual - Getting Started

sergag wrote:

Sorry - I new user in MWS... Where I can find a manual on MWS?

I've uploaded the MWS Advanced Topics Manual recently in another topic here:

http://www.edaboard.com/viewtopic.php?p=492423

I will upload the Getting Started and Tutorials manuals shortly.

eckypting

Added after 43 minutes:

This manual is primarily designed to enable a quick start to CST MICROWAVE
STUDIO®. It is not intended to be a complete reference guide to all the available
features but it will give you an overview of the key concepts. Understanding these
concepts will then allow you to learn how to use the software efficiently with the help of
the online documentation.
The main part of the manual is a so-called Quick Tour (Chapter 3) which will guide you
through the most important features of CST MICROWAVE STUDIO®. We strongly
encourage you to study this chapter carefully.

Table of Contents

CHAPTER 1 — INTRODUCTION................................................................................................................ 3
Welcome.................................................................................................................................... 3
How to Get Started Quickly?...................................................................................................3
What is CST MICROWAVE STUDIO®? ..................................................................................3
Who Uses CST MICROWAVE STUDIO®?..............................................................................4
CST MICROWAVE STUDIO® Key Features............................................................................... 5
General ..................................................................................................................................5
Structure Modeling..................................................................................................................5
Transient Simulator.................................................................................................................5
Frequency Domain Simulator..................................................................................................6
Eigenmode Simulator..............................................................................................................7
Modal Analysis Simulator........................................................................................................7
Visualization and Secondary Result Calculation.....................................................................8
Result Export ..........................................................................................................................8
Automation.............................................................................................................................8
About This Manual ...................................................................................................................... 9
Document Conventions...........................................................................................................9
Your Feedback.......................................................................................................................9
Contacting CST – Computer Simulation Technology................................................................ 10
CST Headquarters ................................................................................................................ 10
Worldwide Distribution Agents ..............................................................................................10
Technical Support .................................................................................................................11
CHAPTER 2 — INSTALLATION............................................................................................................... 12
Installation Requirements.......................................................................................................... 12
Software Requirements.........................................................................................................12
Hardware Requirements .......................................................................................................12
Licensing Options ..................................................................................................................... 12
Installation Instructions ............................................................................................................. 13
Providing Password Information ............................................................................................... 14
CHAPTER 3 — QUICK TOUR .................................................................................................................. 15
Starting the software ................................................................................................................. 15
Overview of the User Interface’s Structure................................................................................ 16
Creating and Viewing Some Simple Structures ........................................................................ 17
Create a First “Brick”.............................................................................................................17
An Overview of the Basic Shapes Available .........................................................................20
Selecting Previously Defined Shapes, Grouping Shapes into Components and Assigning
Material Properties................................................................................................................20
Changing the View................................................................................................................24
Applying Geometric Transformations....................................................................................26
Combine Shapes by Using Boolean Operations ...................................................................28
Pick Points, Edges or Faces from Within the Model .............................................................30
Chamfer and Blend Edges....................................................................................................32
Local Coordinate Systems ....................................................................................................39
2 CST MICROWAVE STUDIO® 5 – Getting Started
The History List .....................................................................................................................42
The History Tree ...................................................................................................................44
Curve Creation......................................................................................................................46
Local Modifications ...............................................................................................................50
Trace Creation ......................................................................................................................52
The First Real World Application Example................................................................................ 54
The Structure ........................................................................................................................54
Start CST MICROWAVE STUDIO®.......................................................................................55
Open the Quick Start Guide..................................................................................................55
Define the Units ....................................................................................................................56
Define the Background Material............................................................................................57
Model the Structure...............................................................................................................57
Define Ports ..........................................................................................................................65
Define the Frequency Range ................................................................................................67
Define Boundary and Symmetry Conditions .........................................................................68
Visualize the Mesh................................................................................................................70
Start the Simulation...............................................................................................................72
Analyze the Port Modes........................................................................................................75
Analyze the S-Parameters ....................................................................................................77
Adaptive Mesh Refinement...................................................................................................80
Analyze the Electromagnetic Field at Various Frequencies ..................................................83
Parameterization of the Model and the Automatic Optimization of the Structure ..................88
Summary............................................................................................................................104
Which Solver to Use? ............................................................................................................. 105
Antenna Computations ........................................................................................................... 108
Simplifying Antenna Farfield Calculations...........................................................................111
Digital Calculations ................................................................................................................. 112
Frequency Domain Computations........................................................................................... 115
Eigenmode (Resonator) Computations................................................................................... 117
Modal Analysis Computations................................................................................................. 120
Discrete Ports ......................................................................................................................... 122
SPICE Network Model Extraction ........................................................................................... 123
Model Order Reduction Based Network Parameter Extraction ...........................................123
Transmission Line Based Network Parameter Extraction ...................................................127
CHAPTER 4 — FINDING FURTHER INFORMATION............................................................................. 131
The Quick Start Guide ............................................................................................................ 131
Tutorials ................................................................................................................................. 132
Examples ............................................................................................................................... 133
Online Reference Documentation ........................................................................................... 133
Referring to the Advanced Topics Manual .............................................................................. 133
Access Technical Support....................................................................................................... 133
Macro Language Documentation............................................................................................ 134
History of Changes ................................................................................................................. 134
APPENDIX A— LIST OF SHORTCUT KEYS......................................................................................... 135
General Shortcut Keys Available in Main Structure View........................................................ 135
Shortcut Keys Available in Edit Fields..................................................................................... 136

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Mindpower

Joined: 23 Feb 2007
Posts: 1

23 Feb 2007 14:57 Re: <CST MWS> A periodic structure+Plane wave problems

Advanced Manual

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shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

09 Jul 2007 21:29 Re: <CST MWS> A periodic structure+Plane wave problems

i am still confused with the waveguide port excitation to find the bandgap of the PBG
surfaces.
normally we select some surface and then assign waveguide port to it.
but where will be our waveguide port located in case of unit cell model of the structure.
i mean for probe fed patch antenna we assign our port to the coaxial cable which is at the back of the ground plane.

can anyone explain in detail how to do it with example posted on this forum.

thanks

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qqqooo

Joined: 06 Oct 2006
Posts: 18

05 Oct 2007 4:53 <CST MWS> A periodic structure+Plane wave problems

can not download!

Added after 22 seconds:

need more points??

Added after 41 seconds:

I am so sorry why it needs so many points?

Added after 24 seconds:

could you give it freely?

echo47

Joined: 07 Apr 2002
Posts: 4206
Helped: 566

05 Oct 2007 6:19 <CST MWS> A periodic structure+Plane wave problems

qqqooo, try clicking the "Free Mirror" links instead of the "Download" links.

Here's more info about the points system:
http://www.edaboard.com/points.php

Pushhead

Joined: 19 Jan 2005
Posts: 195
Helped: 8

05 Oct 2007 8:53 Re: <CST MWS> A periodic structure+Plane wave problems

Quote:

Hi. I am glad to see that this conversation is still alive (started somewhere in 2005...) Very Happy

Regarding your question, try refering to the beginning of this topic, especially to
eckypting's replies - which helped me eventually to implement it in CST.
Where to place the port? Well, I have placed it away from the unit cell in the direction of incidence and de-embedded the reference plane to the surface of the cell.

Good luck
P.

hamid2000

Joined: 07 Aug 2007
Posts: 25
Helped: 1
Location: Tehran

07 Oct 2007 12:28 Re: <CST MWS> A periodic structure+Plane wave problems

Hi
I also want to simulate a 2D Photonic Crystal with CSt MWS 2006, but I can not reach Transmission spectrum and Band Gap region.
Would you please help me with approprite Boundary Condition and Excitation?
I get S12 always ZERO!!! I will be so thankfull to anybody helps me.

please help////////////
Regards

abdoeng

Joined: 22 Feb 2004
Posts: 685
Helped: 14
Location: EGYPT

09 Oct 2007 10:00 <CST MWS> A periodic structure+Plane wave problems

hamid2000,could pls upload ur cst file here

hamid2000

Joined: 07 Aug 2007
Posts: 25
Helped: 1
Location: Tehran

09 Oct 2007 17:20 Re: <CST MWS> A periodic structure+Plane wave problems

I will try to load it..but it is some big(about 6MB !)

I think in another way....such as telling setting and geometry.

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

11 Oct 2007 12:15 Re: <CST MWS> A periodic structure+Plane wave problems

hi pushhead
i have tried your method i got results which seems to be correct but not in good agreement with published results. ( the resonant frequency that is frequency at which phase passes through 0 is less than what i read in journal papers)

also just to confirm we need to model only one structure which is the actual EBG single cell.

because we need to model 3 structures if we use plane wave excitation technique

looking forward for any comments

thanks

Pushhead

Joined: 19 Jan 2005
Posts: 195
Helped: 8

11 Oct 2007 22:58 Re: <CST MWS> A periodic structure+Plane wave problems

Hi,
I'm glad that it works for you. The diffrences you see can be the result of many things like solver settings, mesh setting etc.

If you'll post your model and the article you are trying to follow i'll be able to give it a dipper inspection.

rgdz,
P.

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

13 Oct 2007 13:56 Re: <CST MWS> A periodic structure+Plane wave problems

hi pushhead

thanks for your helpful comments.
i am attaching my simulated model along with the paper with which i am comparing my results. i am getting the resonance frequency at 11.7ghz while in paper for the same structure resonanct frequency is at 10.8ghz.
have a look at it and let me know if you find some clue .

thanks
shahid78

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Pushhead

Joined: 19 Jan 2005
Posts: 195
Helped: 8

31 Oct 2007 12:37 Re: <CST MWS> A periodic structure+Plane wave problems

Hello,

I have reviewed your model and the paper.
First of all, please make sure that you have modeled the shorting pin in the middle correctly. It seems like its material is er=2.2 instead of PEC.
Also,I think that in the paper the use their own FDTD codes instead of a commercial software package. Considering that, your results are "just" 8% higher in frequency than theirs.

Rgdz,
P.

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

01 Nov 2007 0:52 Re: <CST MWS> A periodic structure+Plane wave problems

hi pushhead

thanks for reviewing my model and helpful comments.yah u were right the material of central pin was not pec however when i changed it to pec i got the same result i.e resonant frequency at 11.7ghz.

also one other question have u tried this method with uc ebg because i got error message when i tried to simulate it using this method
the error message is pec material is touching the boundary

i dont know why i m getting this error message.
looking forward for your helpful comments
thanks

Pushhead

Joined: 19 Jan 2005
Posts: 195
Helped: 8

03 Nov 2007 21:36 Re: <CST MWS> A periodic structure+Plane wave problems

Hello again,

I have tried uc ebg in the past and didn't get any error messages. I'll check it out sometime soon and see if there are any "traps" there.

Regarding your model, I've taken another (deeper) look into it and into the paper noticed several things:

1. In the paper they don't mention anything about the metal layer thickness or the shorting pin radius. I did some sweeps and found that resonance changes along with pin radius and metal thickness. Check out the attached picture for metal thickness sweep:

2. The paper uses Periodic Boundary Conditions, whereas in this case you use E/H boundaries.
3. Just to be on the safe side, set the energy level to -50 dB or more so that your S-parameters converge properly (-30 dB wasn't enough in your case)
4. See if you can get a paper that icludes calculations and actual manufacturing and measurements of EBG structures. This would be the best way to test the accuracy of your model.

Regards,
P.

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

04 Nov 2007 15:21 Re: <CST MWS> A periodic structure+Plane wave problems

hi pushhead

thanks for giving some time to resolve my problem
yes you are right by changing the pin radius the resonant frequency changes and i have found that resonant frequency decrease with decrease in pin radius however when radius approaches 0.1mm after that there is no significant change. and for 0.1mm radius my simulated resonant frequency is 11.2ghz so i was not able to approahe the paper resonant frequency of 10.8ghz
h
regarding ucebg simulation i tried this method but when i use E and H boundary conditions for the model the E boundary touches the PEC of the UC EBG cell and cst gives error message for this.

i will be waiting for your reply regarding ucebg simulation using this method.

thanks a lot

piboo

Joined: 06 Feb 2008
Posts: 84
Helped: 2

16 Apr 2008 14:29 <CST MWS> A periodic structure+Plane wave problems

some people uses the waveguide method but the problem si not the same:
with a plane wave you use periodic conditions in ±x and ±y. So you have an infinite substrate in both directions.

However, with the waveguide method, the diagram simulate is for an infinite row of EBG cell.

So that's not totally the same thing.

Don't you think so ?

SAJ25

Joined: 13 Mar 2007
Posts: 223
Helped: 20

18 Oct 2008 7:04 <CST MWS> A periodic structure+Plane wave problems

salam shahid
are you could simulate the PMC in cst?
if yes please tell me as soon as possible

shahid78

Joined: 29 Jul 2006
Posts: 328
Helped: 28

19 Oct 2008 0:51 Re: <CST MWS> A periodic structure+Plane wave problems

hello

well i tried my best to find a way to model PMC structure in cst but as far as i know its not possible in cst

all you can do is to use magnetic boundary condition to simulate PMC

this is all help i can offer at this time

regards