Hi All,
I am designing an L band antenna. The S11 of antenna is below -10dB in the operational band of 1.2GHz - 1.4GHz. However, the dip of S11 is not in the operational band. It is at about 1.05GHz.
Are there any repercussions of sending this antenna for fabrication? What problems might occur if the dip of S11 is not at the center frequency (1.3GHz)? The gain of antenna is fine, as expected.
Many Thanks
Anum
Hi, I think you can get this antenna fabricated as far as the s11 is below -10dB and gain performance (or other parameters etc) is acceptable for your application. However, you need to have a margin for fabrication tolerances .i.e the S11 curve for the fabricated prototype usually shifts a bit (around 5 - 10%). I wuld say the S11 less than -14, -15 dB in the band of interest and spanning a little more than the required spectrum would by pretty good.
Thanks a lot for your kind suggestion. I will definitely work on that.
Hi, you have to check your simulation, especially the excitement of your antenna. If you have a big difference, so be sure that you have a problem with either the excitation or the dimensions of this antenna.
but I can assure you something, for the simulation the curve S11 it will be necessary to fall below -10 dB, but for the realization you can find good results for -6dB or -7 dB only !
Good luck.
You may try to shift the resonance of the antenna the center frequency as you intend. But in agreement with the other colleagues it is irrelevant so long as S11 < -10dB as this means that the antenna is more or less matched. Decreasing S11 than -10 dB will not bring much change in the the incident power on the input of the antenna.
So, your antenna will work good as it is so that S11 measured and simulated can never coincide but always they have large differences in the very small values of S11.
Best wishes
Anum Ahmed Pirkani
If you show the graph then better suggestion can be done... kindly attach if possible.
If your results are reliable it means you could make your antenna about 20% smaller and it will work as well or better, while being cheaper, lighter, smaller and more convenient. 20% saving of materials is a lot of profit advantage in a production run.
If you have S11 below -10dB in your desired frequency, don't worry. You can give it to fabrication. Just make sure you don't want to receive out-of-the-scope signals.
Agreed with Malcolm about the reduction in size and improving the performance if you work upon the structure to shift the resonance. Also agreed with other fellows about the shifts in results when fabrication is done, so keep a margin of at least 2-3dB in your results.
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