Questions about converting structure to finite ground, and appropriate return loss

Respected Sir,

1. i have attached you my file to your personal mail id. plz tell me how to convert it into finite gnd plane? because in fabrication we wcan use only finite gnd plane only right? how much difference will be there in the output?

2. again i am having the same doubt. see instead of giving 40 cells at six GHz, u gave 20 cells at 12 Ghz.my question is return loss is ok if u give 20 cells with6 Ghz at the same time 40 cells at 12 ghz is very good. if i change highest frequency to 10 GHz again result is different. see suppose if the resonant frequency is 5.2 GHz, can i give highest frequency as 5.3/5.4/6/7/8....? how to determine?


with thanks,

kbmani.

Re: to jian

Hi, Kbmanick:

1. To convert your structure to finite ground, you just need to define the No.0 substrate to air and draw the shape of the finite ground plane there. I will e-mail you an example by assuming a finite ground plane size.

2. Your antenna is resonanting at about 5.5 GHz. You set the mesing frequency Fmax = 12. It is quite fine meshing. You can reduce the meshing frequency down to some where slightly above your highest frequency. For example, you are intersted in the frequency response from 5 to 6 GHz. You can define Fmax = 6 GHz and Cells per Wavelength Ncells = 15 to 20. You are supposed to get very similar results if the AEC parameters are set properly.

For your structure, I set Fmax = 12 and Fmax = 7, the frequency responses are very close. The dB(S11) is below - 30 dB for the Fmax = 12 and -22 dB for the Fmax = 7 GHz. As they are, the results are good. If you overlay the 2 curves together, you will see very small difference between the 2 curves.

For antenna applicaitions, if your antenna is resonanting at f0 and you are interested in the frequency range (f0-fb/2, f0+fb/2), you can set the Fmax = f0 + fb/2 with Cells per Wavelength Ncells = 15. Set the AEC Ratio from about 0.05 to 0.1. Normally, it should yield very reliable results. For GaAs IC and RFIC, we may want to increase the meshing density significantly. For IC applications, designers are more interested in the L, C and Q, those values converge much slower. Using regular meshing parameters and much refined meshing, the s-parameters may look the same while there might be siginicant difference in the L, C and Q values. There are guidelines in the manuals and the training materials, please check them. Thanks!

Best regards,

Re: to jian

Respected Sir,

thanks for your reply. please try to clear the following doubts.

1. if i fabricate the antenna my results will vary with the infinte ground plane reults obtained through the simulations. is it so?


2. if the finite gnd plane size is varied then reults also will vary right?

3. after defining the no.0 =air, then how to proceed to make it to finite ground? plz give me step by step procedure. because i could not get any difference except the no.0 layer.

but seeing the layout in mgrid i am able to differentiate.

with thanks,

kbmani

Re: to jian

Hi, Kbmanick:

For patch antennas, the s-parameters should be almost the same for finite or infinite ground. For PIFA, it will be different.

1. You should use finite ground of real size for your model.
2. Please try to find how we do finite ground plane on the Zeland Virtual Training on the web. There are examples there. I am travelling and I don't have time to explain to you right now. Sorry for it.

Best regards,

Jian

Re: to jian

Respected Sir,

i have checked the results for grounded cpw antenna only. but results for the infinte case and finite case results are different. if you find time plz check the file i sent your amil id.


with thanks,

KBMani.

Re: to jian

I will check and get back to you.

Added after 4 hours 17 minutes:

Hi, Kbmanick:

I did not see any file from you. Did you send me an e-mail? Regards.

Re: to jian

Hi, Kbmanick:

Following are the answers:
1. Yes. results will be different for finite ground and infinite ground since the finite ground plane size is not significantly larger than its distance to the cpw fed slot antenna.

2. If the finite ground size is varied, the results will also vary. Basically, the change of ground plane size may change the near field pattern near the antenna obviously. Then, the antenna input impedance will change.

3. After defining the No.0 =air, you just build the finite ground as polygons.

Did I answer your question?

Re: to jian

respected sir,

thanks a lot. i have got enough information. all my doubts are cleared.

with thanks,

kbmani