Does S11 parameter matters from receiver point of view? (Here we are talking about GSM signals. For output reflections I am totally sure, but what about imputs). From my point of view bad impedance matching of antenna should degrade receivers sensitivity. I have offered for my client to do impedance matching. As he was talking with receiver manufacturer, manufacturer declared that S11 is not important and they received only 1dB improvement.
S11 does matter. It makes the same difference to power budget whether it is in the transmitter or the receiver. In the transmitter it is more obvious because the reflected power makes things hot, but if it is in the receiver, then for the same performance a bigger transmitter is needed which also means it still gets hotter!
1 dB improvement is about 25% more power - or 12% increase in range, or improved data rate, or cheaper transmitter.
If they can get a 1 dB improvement then they probably started with a VSWR of 3 which is a return loss of 6 dB. I would consider 10 dB not particularly good but accepted by many people nowadays, but 14 dB (VSWR 1.5) or 15 dB to be reasonable. Going from VSWR 6 to VSWR 1.5 would get about 1 dB improvement.
The unmatched circuit S11 was about -2dB, the manufacturer matched it about -12dB. My as well consider -10dB not very good match, but still reasonable. They said that sensitivity increase by only 1dB. From my point of view it suppose to show even better improvement of sensitivity, unless it is limited by IC.
-2dB S11 means more power is reflected (63%) than gets in (37% or -4.33 dB S21)
-12 dB S11 should receive 93% or -0.28 dB S21, which is a 4 dB improvement.
Thank you Malcolm. I was thinking about around 4 dB improvement. I am trying to figure it out where those 3 dB is missing. Might that be that antenna geometry is not done properly and it will not able to receive properly?
One theoretical question. If I have lets say two different monopole antennas and I have matched them both to -15dB S11. One is lambda/4 and another is shorther. Which will perform better or performance will be the same (if we will not take into consideration antenna aperture).
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