s11 parameter

Hi,

I have a question regarding S11 parameter.
Usually it is sad that antenna should not have S11 above -6dB (or even -10dB).
I have an antenna with acceptable gain (about 3dBi) but with S11 = -4dB. Is this a problem? Why? I know that S11 represents how much power is reflected from the antenna, but if gain is OK, why this should be a problem? Maybe with the power reflected back to the transmitter?

Thanks for the answer.

IMHO, the bigger magnitude of S11 you have the more it is bad coz it means that all you transmitted most will be lost because the reflected is almost equal to the incident. you still need to tune your antenna, it is maybe mismatch with your transmission line, i guess.

vfurlan - in general your statement about reflected power is the answer. in receive antennas the impedance can be quite bad even worse then you've described and still function acceptably. while in the tx side its possible to imagine large reflected power being an issue.

however if you have the opportunity to improve impedance than typically this is done, because now you have a more efficient system.

also if you think of mobile phone antennas, the impedance can exist around - 4 to -6 dB at the band edges easily and still function.

it really depends on the system design, your customers expectations and your expectations.

high s11 is generally due to the mismatch in the transmission line as
jongjong said. By studying impedance matching networks, u can decrease
ur s11.
Study stub matching and quarterwave transformer