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Vehicle antennas
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bigSteve
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Joined: 14 Mar 2009
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PostPosted: Mon Nov 09, 2009 7:35 am    Post subject: Reply with quote

So you are looking at a fractional bandwidth of 0.4%? That is insanely small. Basically, you should only be running this simulation at 470 MHz. If the results are significantly different 1 MHz away, something is incorrect.

This problem should not be difficult. Again, make sure you get correct results for a dipole, then look at a monopole on a finite ground plane (meshed metallic surface), and build your way from there. Good engineering is built on small, solid steps forward.
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engineer
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Joined: 21 Sep 2009
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PostPosted: Mon Nov 09, 2009 9:28 am    Post subject: Reply with quote

Initially I had set these parameters:
star frequency: 460 MHz
end frequency: 480MHz
But the simulation time had become very long, I tried to set a narrower range using the parameters that I reported last message.
I do not understand what the cause of the problem, because when I made the simulation with the same frequency band for the case of the monopole on a finite ground plane; the simulation time were much less long and I got acceptable results.
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bigSteve
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PostPosted: Tue Nov 10, 2009 5:57 am    Post subject: Reply with quote

The time should not increase substantially if you are going from a flat ground plane to modeling a vehicle. I suspect you didn't merge the geometry together before you meshed, or have some other mesh issue.

I can't really say much more without seeing your input files.....
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engineer
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PostPosted: Tue Nov 17, 2009 10:57 am    Post subject: Reply with quote

I managed to reduce the time of the simulation, changing some settings. I removed the calculation of currents and I did a local mesh around the entire structure of the vehicle except on the reference is placed on my antenna. I set a local mesh of lambda / 4, thus making it less dense mesh structure can convey. In your opinion is a good value or advise me to put a better value?

Thanks and good day!
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bigSteve
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PostPosted: Thu Nov 19, 2009 4:06 am    Post subject: Reply with quote

If you want to see if a certain mesh size is valid, then analyze a monopole over a flat ground plane with a good mesh size (lambda/10) and then use your suggested mesh size (lambda/4). This is the type of analysis you should be doing to ensure your work is properly performed.

I would guess lambda/4 is not fine enough.
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engineer
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PostPosted: Sat Nov 21, 2009 1:05 pm    Post subject: Reply with quote

Hello,
I have a problem with a vehicular antenna designs. I'm doing simulations on a frequency band with center frequency of 470 MHz and I have set as the reference impedance of 50 Ohm. I got this from simulation impedance 35.9231-j 0.0592221 for band center frequency of 470 MHz but I'm trying to bring me back to the condition of resonance that is carried over to the case with the real part of impedance of 50 ohms and preferably with reactive part possibly of 0.
What can I do to try to bring me back to this case of resonance? I have to change some settings or do I have to change some value used in the mesh or other?

Thanks and good day!
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bigSteve
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PostPosted: Sat Nov 21, 2009 6:53 pm    Post subject: Reply with quote

The impedance you give sounds about right for a monopole: it should be half of that for what a dipole is.

If you really want the reactance of the dipole to be zero, you can adjust the length very slightly - increasing it by a very small amount will increase the reactance.

Finally, if you wanted the antenna to be matched at 36 Ohms to a 50 Ohm line, in practice you could simply introduce a 14 Ohm resistor in series so no power would be reflected. Another way to do this in practice is to change the length of the monopole such that a series or parallel inductor/capacitor would tune the antenna to be resonant.

In this case, since it is just a simulation, I would alter the load impedance to be 36 Ohms if you are concerned with an exact match.
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engineer
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Joined: 21 Sep 2009
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PostPosted: Sun Nov 22, 2009 8:03 pm    Post subject: Reply with quote

I wanted to use as reference impedance 50 ohm similar to the impedance of a normal coaxial cable. Finally wanted to find a way to get the graph of SVWR (in my case a parable) centered on the band center frequency of 470 MHz. In fact, for the moment the graph of SVWR is centered on a frequency of 468 MHz or less like...
Could you give me some advice or information about how it is to get this result on the graph of SVWR?
Thanks
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bigSteve
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PostPosted: Sun Nov 22, 2009 11:31 pm    Post subject: Reply with quote

It doesn't sound like you are trying very hard.

If the VSWR is centered around 468 MHz, and you want it centered around 470 MHz, what do you think you need to do to the length of the antenna?
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engineer
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PostPosted: Fri Dec 04, 2009 4:53 pm    Post subject: Reply with quote

Is there an option on POSTFEKO to see the trend of current on the wire (vehicular antenna)?
If there is how they work settings and its operation?

Thanks and good day!
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