Data can be encoded by modulating the frequency, amplitude and phase. But I can't find any references for encoding data in the polarization of EM waves (either analog or digital). This is probably for a good reason which I do not understand. Are there any examples of such schemes?
Electronic – Are there any real world examples of encoding data in EM polarization
communicationdigital-communicationsencodingModulationRF
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Best Answer
It certainly can be done, it just isn't very useful, except in certain situations.
For example, ham radio operators sometimes like to do experiments with reflecting signals off the moon (EME, or earth-moon-earth, a.k.a. "moonbounce"). It's useful to transmit with circular polarization, because the reflection comes back with the opposite polarization, which means that the receiving antenna is better at rejecting unwanted terrestrial reflections.
However, in the general case, different polarizations have different propagation characteristics, which makes it difficult to maintain coherency in terms of demodulating a useful payload at the receiving end.