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Vehicle antennas
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engineer
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Joined: 21 Sep 2009
Posts: 14

PostPosted: Mon Sep 21, 2009 4:23 pm    Post subject: Vehicle antennas Reply with quote

Hello everyone, I have to vehicular antenna design for a university thesis.
I have to evaluate the performance of 2 antennas, individually, based on the location that can have on a vehicle. In the first case the antenna is long 1/4 wavelength and in the second case is long 5/8 wavelength.
The parameters I have available are:
1) reference impedance of 50 OHM
2) band center frequency 470 MHz
I want to get results that are: the gain, radiation pattern, bandwidth adaptation.
I should point out that I use the simulator FEKO for this project.
Since it is the first time I use Feko, someone can help me or give advice for this project?
Thanks to everyone for the helpful and good day!

Hello
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bigSteve
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Joined: 14 Mar 2009
Posts: 265

PostPosted: Tue Sep 22, 2009 4:31 am    Post subject: FEKO Reply with quote

Here's what you want to do. First follow the FEKO antenna tutorials given here:

http://www.antenna-theory.com/tutorial/antenna.php

The first thing you need to be able to do is correctly model a half-wave dipole antenna - make sure the radiation pattern, bandwidth, impedance and directivity look right.

Then, place a monopole on top of a metallic box. Make sure you do this right, make sure the results look right, and then you are ready to tackle your problem.

You should model the vehicle using some combination of simple shapes, don't get too fancy here as it won't help the fidelity of your results. Once you have a decent model, place antennas where you want, merge the parts, and you should be good to go.
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engineer
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PostPosted: Tue Sep 22, 2009 9:43 am    Post subject: Reply with quote

Okay I will follow your advice, if I have a problem I'll know you. Thanks for your help and availability.
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engineer
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PostPosted: Sat Oct 17, 2009 12:11 pm    Post subject: Reply with quote

I'm trying to simulate the antenna spin placed on the roof of the car.
But I have doubts about setting up some parameters.
To set up the rays, I have to individually set the radius of the antenna and the radius of the wires that make up the structure of the roof? If you are the radius of the structure is set to the present when the mesh is made of the entire structure (ie antennas + roof)?
When I set the type of material that makes up the roof structure, I specify the default option, or a perfect electrical conductor?
Can recommend other optimal settings to get a correct simulation of my project? In the meantime I'm beginning to study the manual a bit, hoping to find some more information that I could be helpful.

Thanks and Hello!
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bigSteve
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Joined: 14 Mar 2009
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PostPosted: Sat Oct 17, 2009 8:12 pm    Post subject: Reply with quote

I have some questions for you:

Could you clarify what you mean by "antenna spin"?

Why are you using wires to model the roof of the vehicle? Why not use a rectangular box?

And some answers for you:

For your dipole antenna, you should use a mesh size of something like lambda/12. If you make it much finer (like lambda/20), you should not see much difference.

You should use Perfect Electrical Conductor (PEC) for all materials.

You can independently set the radius of different wires in FEKO, by meshing selected elements (geometries), one at a time, instead of using the "mesh all" command. But then you need to select all the meshes at the end and then select "merge coincident vertices" so the meshes are attached.
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engineer
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PostPosted: Sun Oct 18, 2009 12:22 pm    Post subject: Reply with quote

Maybe I have not explained well I am sorry.

1) I meant the wire antenna. I built using the line.
2)For the roof of the car, I built using the polygon and I set face type as default.
Basically I built a rectangle of length 1.508 m (axis x) and 1.624 m (axis y).
Then I made the union between the rectangle and line.
And finally I made the mesh of the entire structure (antenna + roof).

I have another question, but I must also enter the request S-parameters or not?
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bigSteve
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PostPosted: Sun Oct 18, 2009 7:00 pm    Post subject: Reply with quote

You have to request the S-parameters if you want them. Basically you will look at S11 and will be able to see the bandwidth and impedance of the antenna from that.
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engineer
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PostPosted: Sat Oct 24, 2009 11:28 am    Post subject: Reply with quote

When I go on postfeko where I find the option to see the bandwidth?
I realized the metallic box with a monopole, when I run the simulation with a single frequency does everything correctly.
But when I run the simulation using multiple frequencies through continuos range option, I get a strange error and does not end the simulation. What causes this error since I have not found anything about it?
The error reported is this: error 31027

Thanks!
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bigSteve
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PostPosted: Sun Oct 25, 2009 6:12 pm    Post subject: Reply with quote

There is no "bandwidth" result that FEKO will put out for you. This is because bandwidth has no strict definition - for instance, you can define the bandwidth of an antenna to be where S11 < -6 dB, or define the bandwidth to be the frequency range over which VSWR<2.5, or define it to be where the antenna efficiency is greater than 30%. So you have to choose the bandwidth metric and then figure it out on your own.

I'm not sure what your error is for your simulations. If you can run a single frequency, but not multiple frequencies, I would guess that you are running an extremely large bandwidth, so that for fixed mesh/segment size, the FEKO solver does not work well. Try using a smaller frequency range, or just run the solver multiple times at a single frequency.
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engineer
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PostPosted: Mon Nov 02, 2009 11:27 am    Post subject: Reply with quote

When I start the simulation with feko I have not problems, but when I start postfeko I have a problem about displaying far fields.
In fact the radiation field is not displayed in the position where the antenna is located with its voltage source but appears far from the antenna using centered around the origin of the axes x, y, z.
I checked the settings but I seem to be correct, how to solve the problem because I want to see a radiation field centered on the antenna with its voltage source ?
Thanks and good day!
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bigSteve
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PostPosted: Tue Nov 03, 2009 5:31 am    Post subject: Reply with quote

Postfeko always centers the radiation pattern around the origin. One way to remedy this - so that the antenna is also at the origin - is to go into cadfeko, select all of your geometry components, right click on them, and select translate. Them translate your entire geometry such that antenna is now at the origin. Then remesh, and rerun your simulation. Then in postfeko you will have your radiation pattern centered on your antenna.
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engineer
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PostPosted: Tue Nov 03, 2009 10:00 am    Post subject: Reply with quote

Ok I'll try as you suggested, thanks for the help.
But my question is this, I can have a radiation pattern in a different position from origin of the axes?

I traslate the vehicle in order to have the part where the antenna is
positioned at the origin of the axes.
But the antenna is at a certain height from the origin of the axes. So how do I get a radiation pattern positioned on the height of the antenna and not the origin of the axes?
Thanks
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engineer
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Joined: 21 Sep 2009
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PostPosted: Sun Nov 08, 2009 2:09 pm    Post subject: Reply with quote

Hello
I'm doing a simulation on a certain frequency band, I've set this thing on continuos (interpolated) range. I set the start frequency and end frequency but I left everything else default. The problem is that the simulation time is very long, and to obtain a final result takes long time.
I should point out that my license supports a maximum number of 1 CPUs and and data that I see on the simulation are as follows:
4 metallic wire segments in free space
8156 metallic triangles in free space

Is there a way to decrease the simulation time because I'm simulating a certain band of frequencies?
Also in the settings there is an option to set maximum number of samples. What number should I set to have an acceptable simulation result that does not create problems of inaccurate if not fully converged?

Thanks and good day!
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bigSteve
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PostPosted: Sun Nov 08, 2009 9:04 pm    Post subject: Reply with quote

What frequency range are you using?
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engineer
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PostPosted: Sun Nov 08, 2009 10:11 pm    Post subject: Reply with quote

star frequency: 469 MHz
end frequency: 471MHz
The frequency band center is the frequency that I used the top that was 470 MHz.
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