I don't agree. An antenna, that has low losses by design, e.g. a wire antenna with good conductivity is known to have low losses. Than the relation is obvious.There is no specific relationship between S11 and radiated power
There is no easier way than measure the field strength for both polarizations, rotating the antenna in two axis in an anechoic chamber. Near field effects and limited calibration accuracy of the measurement antenna has to be considered.Also, how would you measure radiated power? Add to it how would you measure gain?
It's called conservation of energy. Of course, no real antenna is exactly lossless, but it can be low loss."If the antenna is lossless, all input power will be either reflected or radiated." Why is that?
It's basically simple. If you assume a lossless antenna, which is just another word for "that all power accepted (after impedance mismatch) by antenna is radiated", then you can derive the equation from elementary network theory (s11²+s21²=1). If the losses are low, the result will be essentially the same.Maybe, if someone could present an equation that links the two.
It is misleading to generalize like that.
I feel tempted to discuss some details, e.g. what it means if s11 only dips by 2 dB. But perhaps we can agree, that my consideration shouldn't be applied to electrical small antennas.At least half of the antennas I work with are electrically small
In the reported case, it means the opposite: a badly matched antenna is reflecting most of the supplied energy rather than radiating it.-2dB it means out of 100% power
Yes. But in addition, it's helpful to understand, what can be concluded from S11.Usually, all you care about is how much power goes from point A to point B. S11 can be a misleading answer to that question.
Measurements of an antenna embedded in an enviroment, e.g. a mobile antenna considering the user is a more complicated problem. It goes beyond clearly specified antenna properties, that are determined in an an-echoic chamber without any disturbing objects. Objects near to the antenna will surely show in the S11, and can change it in both directions, tune as well as de-tune the antenna. But generally, if lossy objects are involved, the s11 variation can't be translated into radiation efficiency change.but in case the antenna is near other lossy objects like human body, the power radiated would be decreased due to losses (due to power absorbed by human body), but S11 should remain the same.
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