Antennas : About RFID Radio Frequency Identification

What's the difference between a linearly polarized antenna and a circular polarized antenna? Here's the detailed explanation.

Unlike water waves, electromagnetic waves are not influenced by gravity, and the electric field can point in any direction in the plane perpendicular to the direction of propagation. Because human beings are gravitationally challenged, it is most common to orient linearly polarized antennas either vertically or horizontally. It is also possible for the direction of polarization to be time dependent. For example, the electric field can rotate around the axis of propagation as a function of time, without changing its magnitude, producing circularly polarized radiation

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