Some problems in IE3D simulation

[hsean]

Hi all,

I tried to duplicate the simulation results of an antenna mentioned in a paper.
The antenna is a CPW-fed slot antenna.
I was unable to get even a similar simulation result to the one shown in the paper.
Could anyone help me to check if there is anything wrong with my simulation setup? I tried both magnetic current and electric current simulation, but none of both gave me satisfied results. Pleas help me out. Thank you very much.

The files are attached.

 

[ADS_RFMW]

Why can't u use ADS-momentum.give exact results.

 

[khouly]

i have used ADS momentum , it is great . the acuracy is very good and give a very close results to simulation , and have a very good features like model composer and EM circuit co simulation

khouly

 

[jian]

Hi, hsean:

I checked the structure. I see some incorrect parameters "t=1.6 and l=1.3". I assume they are "t=1.3 and l=1.6". Otherwise, I don't see other mis-match in the parameters between your built of geometry and the one discussed in the paper.

However, for your finite GND model, you define -1 port over a very wide edge. This normally should be avoided. Please see my suggested improved model attached.

The results for the m-current model for infinite ground and e-current model for finite ground are close. They predict the resonance at about 6.1 to 6.15 GHz with minium |S(1,1)| at around -14 dB. Changes in meshing do not affect the results. They should be reliable. They do not match what is presented on the paper. Such thing happens and it is quite possible some dimensions are incorrectly documented.

From what I see, given the dimensions and the parameters defined, the IE3D results should be quite reliable.

Regards,

 

[hsean]

Thanks a lot for all your helpful response.

Dr. Jian, I'd like to ask one more question :
Recently, I design several CPW-fed slot antenna and simulate with IE3D.
The measured bandwidths for most of them match to the simulated results.
However, the center resonant frequencies are all shifted (e.g. from 5.75 GHz to 5.5 G). I can't figure out what would be the cause of that phenomenon.
Is it possible that the infinite ground plane assumption in the simulation might cause the discrepancy?

Thank you.

 

[jian]

Hi, Hsean:

It really depends upon many factors.

For many slot antennas, ground plane size can be quite critical. The finite GND may be part of the radiators. If you don't model it as a finite GND, it may (or may not) yield some shift. For the CPW fed slot antenna with the dimensions given on the paper you enclosed in this thread, using the m-current model of infinite GND, the calculated resonant frequency is about 6.1 GHz. The e-current model of finite GND (30 by 30 mm defined in the paper), the resonant frequency is 6.15 GHz. Also, the S11 curve is slightly different. I have done some convergence study on both models and they are converged. The difference between them should be due to the GND. Interestingly, the authors use IE3D for the paper and the resonance frequency is 5.8 GHz. I believe they are correct data. However, it is possible some dimensions are not documented correctly on the paper so that we could not duplicate the resutls here.

I have mentioned it before in some other threads. Field created by a slot antenna may spread quite a big region. Significant field or wave may hit the boundary of the GND and it may reflect back and the reflection is strong enough to change the antenna's impedance. For microstrip antennas, most of the field is confined inside the cavity formed by the patch antenna and GND, and the field leaks out is much weaker. The reflected back field from the edge of the GND is even weaker and it will not affect the Zin of the antenna much. That is why you don't see much effects on Zin for microstrip antennas from GND.

For slot antennas, I do suggest designers to check both the infinite GND and finite GND model. The finite GND model should yield more realistic results in case there are differences.

There are also other factors may affect the resonant frequency. The most important one is the permittivity. The permittivity value from spec may not be very accurate. I think it may differ from different batches or the same batch of the same product. You may need to make sure the permittiivty is right in order to get consistent results with high accuracy.

Best regards,

 

[nazanin]

hello Dr jian
please helped to me
i want use from cavity backed ground plane in software ie3d
also i want creat slot in ground plane .

 

[jian]

You can send e-mails to me at: jian@zeland.com

 

[maxwellian]

Why can't u use ADS-momentum.give exact results.

ADS_RFMW: You need to stop sending the list all these "Use ADS" and "Use Momentum" messages. I am guessing that you sell the software or that you work for Agilent.

No EM analysis software gives "exact" results. They all give error. The question the engineer has to ask is:
"For my application, which EM tool consistently yields the lowest error, in what I consider a reasonably length of simulation time?"

I would consider Momentum to be no more accurate than IE3D; they are both based on the same basic approach to solving problems using the planar Method of Moments.