Need help with antenna (IE3D) [very urgent plz]

[Alberich]

Hi every one,
I designed and simulated a single band PIFA, wich has a resonnat frequnecy =1.88 GHz. and a 18 % band width that make it cover DCS PCS and DECT.
the matter is that for all those caractersitcs I refered to the VSWR and S11. So when my professor sow it he told me that it was false and this antenna is not applicable because he told that we must refer to the impedance graph.
I am sure that what I do is just because it is the technique used in all the articles I saw. Son can any one see the attached files and tell me if this antenna is applicable and if my measure method is just.
Please it is very urgent guys thanks in advance.
Best regards.

 

[jian]

Hi, Alberich:

I checked it. It is a good design. |S11| is quite low over a wide frequency range. As Zin is concerned, it is close to 50-ohms in a wide frequency range. When 50-ohm normalized |S11| is low, the Zin should be close to 50-ohms.

The only thing you may want to improve is to use Automatic Edge Cells. It will make the results more accurate.

Best regards,

 

[Alberich]

Thanks Dr Jian for ur help,
the matter is that how can I explain to my professor that this design is just, he told me that in the resonnance the Re(Zin) must be maximum, and he told that the resonnance I get is what he called an "anti resonnance" and such as antennas are not applicable.
Really I don't know what to do, I told him that as long as the |S11| is minimum it is a resonnance. and as long as I get a VSWR under 2 it is a band width.
So if u have an answer to that, it would be great.

For the simulation I chked the AEC I make it about 10 %. and the results changes a little bit but it is not a matter.

thanks in advance.
Best regards

 

[cuongtran]

I have the same problem, in the f resonance, R is not the max, but near the point of f res, aproxi 5% I have the max of R, so is it acceptable, thanks in advance mr Jian!

 

[jian]

Hi, Alberich:

I don't think it is necessary to get R to maximum at the desired frequency. We just need it to have a good match at the frequency. I am not sure why your professor requires you to get R at maximum at the resonant frequency point. Most good antennas do not have such characteristics. Just take the simplest antenna, a thin dipole antenna as an example. Its R is about 73 ohms and X is about 0 when the dipole length L is about 0.475 lambda. If you plot the frequency response of R, it is monotonically increaseing until the L is approaching one wavelength. However, its resonance at about 0.475 lambda is a good one and it is matched to about 75 ohms. It is a good antenna.

Most antennas' reonances are the so-called loaded resonances. At the resonance point, the maxium R and zero X do not happen at the same frequency. I think the most important thing is that you can achieve the desired R (normally 50-ohms) with X = at the frequency you want. It really does not matter whether the R is at maximum at the frequency point. When you achieve the R = Zc and X = 0 at the frequency point, you will get minimum return loss and your antenna achieve the best efficiency and gain for the given configuration.

Regards.

 

[streamlet]

to Alberich:
I am somewhat confused by your statement.

You see, "anti-resonance" means parallel resonance which delivers a maximum R. Your prof. required you to achieve a maximum R while wanting to dump the parallel resonance, how to achieve that?! There is a self-contradiction in your statement.

In my opinion, parallel resonance is not a good situation for proper antenna operation, generally speaking, because then they mostly have too large a R to be matched with common feeding lines.

Added after 27 minutes:

For illustration, I add a set of simulation curves here. Note that the performance of this example is not optimized, just for illustration.

The working status of your antenna is just like around 2.7GHz in my example, where also a best matching appears. Refer to the impedance curve, you can see the antenna is not purely neither parallel resonance nor series resonance.