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Wave plane or waveguide port in CST

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abuantenna

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wave plane

Hi,

I have read recently about wave plane in CST and its benefit to drive linear or circular polarization signal. I would like to know when to use wave plane and when to use waveguide port? I'm fully confusing about this. My goal to know what I have to use with waveguide and Microstrip antennas to get s11, far field and behaviour of linear and circular polarization.
Thanks in advance.
 

dch316

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site:edaboard.com cst waveguide port

hi,
plane wave excitation is useful for simulating radar cross sections (RCS). If your intention is to simulate a far field radiation pattern in a microstrip antenna then you can use either a discret port or a wavegide port but be aware that with discrete ports you´ll get unaccurate solution for S11. With waveguide port (I use it always if possible) you'll have a good solution for both farfield (with polarization) and S11.
For the polarization, choose ludwig3 coordinates for linear polarization (vertical or horizontal) and spherical for Circularly polarised antennas.
good luck
 

abuantenna

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waveguide ports

Hello Mr. Dch316,

Thankks a lot for your reply. It seems you have good experience with CST.
Actually, I'm using waveguide ports and it seems no problem so far. In fact, I'd like to to check polarization effect of antennas by driving my antennas by circular or elliptical polarization signal and see the reaction.
I tried plane wave but results are much worse than waveguide port for simple horn antenna. I think should be some special setting for plane wave. isn't it ?
I'm using 1 V/m and the propagation in z direction.
Let me summerize it in my words:
1- It is better always to use waveguide ports.
2- Discrete ports give some errors in s11. Is it something from your experience or it is written somewhere? what about switching to HFSS? is it better for high frequencies design like 300 GHz patches or horns?
3- Is it ok to check antenna polarization act by driving it with different polarization port, or just to check far field left hand and right hand results with simple port?
4- You said: For the polarization, choose ludwig3 coordinates for linear polarization (vertical or horizontal) and spherical for Circularly polarised antennas.
Do you mean during port definition? Sorry I'm new in CST world.
5- Do you have any idea of the meaning of left polarization and right polarization in the far field results in CST? They are almost the same for different antenna structures. I don't know why?



Hope the idea is clearer now.

Regards
 

dch316

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waveguide cst help

abuantenna,
remember that, due to the recipocal theorem, an antenna perfoms exactly in the same way as a transmitter or a receiver. That means you dont need to generate a plane wave excitation to see the performance of your receiving antenna, just run a far field simulation.
For example, if you have a dipole along the x axis it will mostly radiate in the X direction. However it will also radiate with lower level in the Y direction; the difference between them is known as crosspolar discrimination (XPD).
Discrete ports should be used only when waveguide ports cant. Its in the help or in some tutorial. Anyway its true because ive tested it.
I havent worked with FHSS but people I know is changing to CST (?) because its faster.
you choose ludwig3 or spherical in plot properties/axes, after far field simulation in the farfield plots.
The definition of right polarisation and left polarisation is the standard definition, see for example the book of Constantine A. Balanis (or another one).
Finally, you cant choose the polarisation of an antenna port. The antenna itself forces its own polarisation. For example, in the case of the dipole, with ludwig3 coordinates you will see a high level of radiation in the horizontal polarisation but a low level in the vertical; this means the antenna radiates in a linear horizontal polarization. If you want vertical polarization then rotate the dipole by 90 degrees.
I hope these will be useful for you
sorry for my english hehe
 
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abuantenna

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waveguide ports on cst

Hello Mr. Dch316,

Your answer is absolutely fine but excite me for more questions.
I totally understand the linear and circular polarization.
What I can't understand that how to show that in CST and what's the pattern will be for each of polarization or when we have dual polarization.

Let me take the same example you mentioned about dipole. If you open the example in CST, it is dipole in z-direction. Then, if you go to far field and switch to ludwig 3 (which is something I'm not sure that I understood from CST help).
You will see same level of signal in both horizontal and vertical. Of course, in opposite direction. So, is this means that this dipole is horizontal and vertical polarized, means circular polarized?!!

From other hand, let me put it is organized way by another one question.
What shall we see in ludwig 3 horizontal and vertical for each case:
1-Vertical linear polarization
2-Horizontal linear polarization
3-Right hand circular polarized
4-Left hand circular polarized
5-Dual circular polarized antenna

Sorry for all these questions.
Regards
 

dch316

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ludwig3 cst

abuantenna said:
Hello Mr. Dch316,

Your answer is absolutely fine but excite me for more questions.
I totally understand the linear and circular polarization.
What I can't understand that how to show that in CST and what's the pattern will be for each of polarization or when we have dual polarization.

Let me take the same example you mentioned about dipole. If you open the example in CST, it is dipole in z-direction. Then, if you go to far field and switch to ludwig 3 (which is something I'm not sure that I understood from CST help).
You will see same level of signal in both horizontal and vertical. Of course, in opposite direction. So, is this means that this dipole is horizontal and vertical polarized, means circular polarized?!!

From other hand, let me put it is organized way by another one question.
What shall we see in ludwig 3 horizontal and vertical for each case:
1-Vertical linear polarization
2-Horizontal linear polarization
3-Right hand circular polarized
4-Left hand circular polarized
5-Dual circular polarized antenna

Sorry for all these questions.
Regards

Dear Abuantenna,
The example of the dipole in CST is a little tricky; let me explain: if you choose ludwig3 coordinates you MUST have the direction of maximum radiation on the Z axes, and the direction of the E field in this direction MUST be either X (ludwig horizontal) or Y (Ludwig vertical); These implies that a dipole must be placed along the X axes (X or ludwig horizontal will be Copolar polarisation and Y or ludwig vertical will be Crosspolar) or along the Y axes (Y or vertical will be Copolar polarisation and X or horizontal will be Crosspolar). In the example do this: rotate the driven element (the dipole) 90º (the dipole will be along the X or the Y axes)and redefine the discrete port. Then run the transient solver and that's it!!
In the example by default on CST, the polarisation is linear but in the Z direction, then ludwig 3 doesnt work because both X and Y directions are crosspolar E field (thats why they're equal). There is no circular polarization, that means that both left and Right polarisation are equal.
I hope this will help you a lot.

Finally here you have the answers to you questions, ALWAYS supposing the dipole is oriented along the Y axes:

1. Vertical linear polarisation (Ludwig3) is the Copolar component.Then its maximum in all directions
2. Horizontal linear polarisation(Ludwig3) is the Xpolar component. Then its is minimum.
3 It has no sense
4 It has no sense but it should be equal to point 3.
5 It has no sense.

Regards
 

abuantenna

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where ludwig3 cst

Hello Dch316,

I hope my questions not give you any kind of weariness.
Let me say it in my words and correct me if it is wrong:
1-Ludwig 3 make sense when the maximum radiation going in z-direction.
2-With Ludwig 3 we are able to see only linear polarization, and to check if it is vertical or horizontal.
3-If #1 is ok, then we will have two components in Ludwig 3. If the maximum is the vertical component, then it is vertical polarized antenna and vise-cersa.

If the above points are ok, then let me back to the first question:
Q- How I can be sure from far field results in CST for some kind of antennas like (corrugated or dual mode) that these antennas are really deliver dual polarization signal (circular LHS and RHS)

Is there any possibility for that in CST or not?

Regards
 

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wave plane or waveguide, edaboard

abuantenna said:
Hello Dch316,

I hope my questions not give you any kind of weariness.
Let me say it in my words and correct me if it is wrong:
1-Ludwig 3 make sense when the maximum radiation going in z-direction.
2-With Ludwig 3 we are able to see only linear polarization, and to check if it is vertical or horizontal.
3-If #1 is ok, then we will have two components in Ludwig 3. If the maximum is the vertical component, then it is vertical polarized antenna and vise-cersa.

If the above points are ok, then let me back to the first question:
Q- How I can be sure from far field results in CST for some kind of antennas like (corrugated or dual mode) that these antennas are really deliver dual polarization signal (circular LHS and RHS)

Is there any possibility for that in CST or not?

Regards

hi abuantenna,
you're right in all 3 points above, ludwig 3 only makes sense with linear polarisation and when the maximum radiation is along the z direction.However, if you have a dipole like the one in the example in CST you can change the axes (plot properties/axes) and put the z' axes in the direction of maximum radiation and the x' or y' aligned with the dipole; ludwig 3 makes sense now with x',y',z' axes :D

next Q:
if you have a dual polarised antenna you will have two ports (let's put as an example a cross diple, one dipole along the y axes and the other along the x axes). Then, on ludwig 3 when you look at the rad pattern of the 'x-dipole' youll have a powerful ludwig horizontal polarisation but a very low vertical and viceversa with the 'y-dipole'.
If you had a horn and you would like to know its polarisation you would do the following:
simulate it and put ludwig and spherical coordinates. The most powerful component (vertical or horizontal or LHCP or RHCP) would be the plarisation of the antenna. The other components would show you the power delivered to space (or received by the antenna, remember the reciprocal theorem) on those other polarisations. For example if the antenna was RHCP you would see a powerful level for right pol but low level or left pol. With ludwig3 you would see the same power in vertical and horizontal (supposing a simmetric horn), both lower than RHCP of course. I encourage you to work on a crossed dipole as the example I told you above.
By the way, how is it done to give a thanks message (I have received 3 from you). I want to thank somebody who helped me and dont know how. Tank you very much

regards.
 

    abuantenna

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abuantenna

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discrete port in cst

Hello,

You can just click "helped me" button to thank any body respond to your post.

I did the simulation for two dipoles. One will expect that this structure will give dual polarization. That what I've got as well. Comparable levels in both vertical and horizontal in ludwig coordinate.

But
I did another simulations for conical, corrugated and dual mode horns.
All of them radiate in the z-direction and symmetrical in xy-plane.
I expect that I'll get comparable components for vertical and horizontal components.
but
I've got the same result in spherical coordinate for left and right power pattern. For ludwig 3, the potential level in vertical only and very small in horizontal.

It is exactly the same result of dipole in y-direction.

So, it is surprise, isn't it?? As these horns should give dual polarization not vertical linear one only.
My question in this case: Am I doing something wrong in settings or still there is some misunderstanding?

Regards
 

dch316

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site:edaboard.com cst tem mode wave

abuantenna said:
Hello,

You can just click "helped me" button to thank any body respond to your post.

I did the simulation for two dipoles. One will expect that this structure will give dual polarization. That what I've got as well. Comparable levels in both vertical and horizontal in ludwig coordinate.

But
I did another simulations for conical, corrugated and dual mode horns.
All of them radiate in the z-direction and symmetrical in xy-plane.
I expect that I'll get comparable components for vertical and horizontal components.
but
I've got the same result in spherical coordinate for left and right power pattern. For ludwig 3, the potential level in vertical only and very small in horizontal.

It is exactly the same result of dipole in y-direction.

So, it is surprise, isn't it?? As these horns should give dual polarization not vertical linear one only.
My question in this case: Am I doing something wrong in settings or still there is some misunderstanding?

Regards

HI,
congratulations for your progress. I dont think you`re doing something wrong in settings. It really surprises me. check the working frequency. Perhaps the dimensions of the horn are not well chosen. In this case I think I will not be able to help you, I'm sorry. I am sure you will find the error though. good luck
kind regards
 

abuantenna

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ludwig 3 horizontal

Hello,

Actually, I designed myself these horns and I calculate all dimensions very careful. I took all points (in my mind) of cutoff frequencies and special dimensions of corrugated horn.

I'll try to study all results again.

Regards
 

dpuentegarcia

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wave plane working

Hi everyone,

I have a problem. I am simulating a FSS cell in CST Studio and I want to calculate the reflection coefficient in a frequency range with a plane wave (TEM mode). I am using a waveguide, but I am not sure which mode I am exciting with a waveguide. Any of you can you tell me how to excite a TEM mode with a waveguide port.

Thanks in advance,

David
 

gachedo

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Hi everybody!

Plz help me define a waveguide port for planar dipole.

I want to design RFID antenna matching IC with impedance = 10-245j ohms at resonant frequency 865.5 MHZ. I can just define discrete port with lumped elements, so I define port with impedance 10 ohms and lumped element 4.716pF. I think it can express IC input. Is it OK?

And I have another question: Can CST calculate characteristic impedance ?

Plz help! I don't have time enough to finish thesis!
HUHU!
 

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