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Multiple Far Field Request

Altair Forum User

Hi.

Can i request more than 1 far field in the same session?

And if i can, how?

I have multiple antennas with different location and i want to plot gain of these antennas seperately.

When i request a far field, it always plots the gain pattern at (0,0,0). If i shift it, it only shifts the pattern, not the calculation point of the far field.

So what i do is always calculate and plot the far field of the antenna located at (0,0,0).

I currently have FEKO 2017 with Student Licence.

Thanks.

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JIF

Hello mustaphos,

Can i request more than 1 far field in the same session?

Yes, definitely. You can add as many far field requests as you want. They can be in the same configuration, different configurations and also have different origins (and orientations).

And if i can, how?

That depends on what you mean and what you want. I'll explain below.

I have multiple antennas with different location and i want to plot gain of these antennas seperately.

When i request a far field, it always plots the gain pattern at (0,0,0). If i shift it, it only shifts the pattern, not the calculation point of the far field.

So what i do is always calculate and plot the far field of the antenna located at (0,0,0).

If you have a model with multiple antennas and you want to calculate the gain of each antenna, taking the other antennas (structures) into account, the best is to use multiple configurations. Each configuration then has a single source (for that particular antenna) and all other antennas are loaded correctly (if they need to be loaded - FEKO models an ideal voltage source and thus any system impedance would have to be added).

Regarding the location of the far filed, the origin of the far field can be changed in CADFEKO on the 'Workplane' tab of the far field request. This will display the far field at that origin and the far field request will also be at that point and not at the origin. If you move the far field in POSTFEKO, as you noted, it simply changes where it is displayed and not the far field request itself.

It is also possible to calculate the far field taking only a subset of your model into account - have a look at the 'Scope' tab to limit the elements to a subset. Just note that the far field will still take all the sources into account, it is just the radiation that considers only a subset of the model.

I hope this helps. It is a bit difficult to give more 'to the point' answers without an example.

Altair Forum User

Hello mustaphos,

Yes, definitely. You can add as many far field requests as you want. They can be in the same configuration, different configurations and also have different origins (and orientations).

That depends on what you mean and what you want. I'll explain below.

If you have a model with multiple antennas and you want to calculate the gain of each antenna, taking the other antennas (structures) into account, the best is to use multiple configurations. Each configuration then has a single source (for that particular antenna) and all other antennas are loaded correctly (if they need to be loaded - FEKO models an ideal voltage source and thus any system impedance would have to be added).

Regarding the location of the far filed, the origin of the far field can be changed in CADFEKO on the 'Workplane' tab of the far field request. This will display the far field at that origin and the far field request will also be at that point and not at the origin. If you move the far field in POSTFEKO, as you noted, it simply changes where it is displayed and not the far field request itself.

It is also possible to calculate the far field taking only a subset of your model into account - have a look at the 'Scope' tab to limit the elements to a subset. Just note that the far field will still take all the sources into account, it is just the radiation that considers only a subset of the model.

I hope this helps. It is a bit difficult to give more 'to the point' answers without an example.

Thanks for your answer sir.

I attached my example construction below.

If you have enough time, please show me how it works.

Regards...

Edit:

I tried to create 2 far field in a different config area with different antenna, but it show the same pattern.

I set the origin of the far field request as which the ports of the antenna 1 and antenna 2 located but it shows me the exactly same pattern with different start point. Which is i think is wrong since the pattern of the gain of the first antenna is true which has higher gain towards out of the 3 align antenna the second antenna which is between antenna 3 and antenna 4 should have different gain pattern. And also antenna 3 and antenna 4 should have different gain from antenna 1 and 2, too.

Unable to find an attachment - read this blog

JIF

The problem is that your model consists of 4 antennas and all of them are excited at the same time (one configuration) and you are requesting the far field at different positions. The phase of the far electric field will change as you move the origin around, but the magnitude will remain constant. Do you agree that this is expected. It should then be clear that if you calculate the gain or directivity (scalar values), that they will remain constant, no matter the origin.

What you are trying to calculate is the gain of one of the antennas, in the presence of the other antennas. Thus, you should create 4 configurations and in each configuration, only one of the antennas have a source active (for ideal sources, simply not adding a source for the other three antennas would be correct, but as noted earlier, if the antennas are supposed to 'see' some system impedance, the other three need to be loaded by the system impedance). If you are interested only in the gain (and the far electric field phase is not important to your investigation), a single far field request needs to be added in each configuration (the same far field for all four configurations).

Now that you know what to do, I'll explain how to do it (starting with the model that you attached):

Duplicate your configuration so that you have 4 configurations.
Select the Configuration tab (next to the Construction tab) so that you can see the source in the tree for your selected configuration.
Click on the gear icon (configuration settings) and set the sources to be per configuration. This will allow you to have different sources in different configurations.
Select the first configuration and delete source 2, 3 and 4.
Select the second configuration and delete source 1, 3 and 4.
Continue this process until there is one source in each configuration (each configuration has a different source).
All four configurations should have the same far field request (was copied when you copied the configurations).
Run the model and compare the patterns in POSTFEKO. Note that you will have to add the far field to the 3D view and then change the configuration (top right, in the panel) and it will then show the far field for that configuration.

Altair Forum User

The problem is that your model consists of 4 antennas and all of them are excited at the same time (one configuration) and you are requesting the far field at different positions. The phase of the far electric field will change as you move the origin around, but the magnitude will remain constant. Do you agree that this is expected. It should then be clear that if you calculate the gain or directivity (scalar values), that they will remain constant, no matter the origin.

What you are trying to calculate is the gain of one of the antennas, in the presence of the other antennas. Thus, you should create 4 configurations and in each configuration, only one of the antennas have a source active (for ideal sources, simply not adding a source for the other three antennas would be correct, but as noted earlier, if the antennas are supposed to 'see' some system impedance, the other three need to be loaded by the system impedance). If you are interested only in the gain (and the far electric field phase is not important to your investigation), a single far field request needs to be added in each configuration (the same far field for all four configurations).

Now that you know what to do, I'll explain how to do it (starting with the model that you attached):

Duplicate your configuration so that you have 4 configurations.

Select the Configuration tab (next to the Construction tab) so that you can see the source in the tree for your selected configuration.

Click on the gear icon (configuration settings) and set the sources to be per configuration. This will allow you to have different sources in different configurations.

Select the first configuration and delete source 2, 3 and 4.

Select the second configuration and delete source 1, 3 and 4.

Continue this process until there is one source in each configuration (each configuration has a different source).

All four configurations should have the same far field request (was copied when you copied the configurations).

Run the model and compare the patterns in POSTFEKO. Note that you will have to add the far field to the 3D view and then change the configuration (top right, in the panel) and it will then show the far field for that configuration.

I did what you say and i am able to run the simulation and can be able to all far field request of each antenna seperately.

I am simulating one antenna and get maximum gain value of 1.35 but when i simulate 8 antenna i get 1.50.

Is this true?

I am simulating each antenna with 128MHz and seperate ports.

Shouldnt the gain outcomes as less than the gain i saw in one antenna situation?

I am seeing the disturbances from other antennas clearly, and i think they are correct.

But i did not quite understand why they have more gains in some directions.

I added some screenshots.

Thanks for answers...

<?xml version="1.0" encoding="UTF-8"?>

JIF

I don't know exactly what your models look like, but getting more gain is not unexpected. Your model is lossless (as far as I can see) and has no loads. Thus, we can talk about directivity instead of gain. The directivity is simply a measure of the amount of field radiated in one direction compared to a uniform distribution over a sphere. If you start with an isotropic radiator (something that does not exist) and you somehow reduce the directivity in one direction, the directivety in other direction would have to increase. It is the same in your case. The easiest way to probably think about this is by thinking of a Yagi Uda antenna - it has more gain than a single dipole.

Does that help? Or did I misunderstand the question / problem?