Reader antennas, like tag antennas, may also assume form factors appropriate to their application. This includes antennas fitted to dock doors, embedded in store shelves or racks, fitted within a point-of-sale terminal, or integrated into the guide rails of conveyor equipment. Some antennas are especially designed to read tag data of tags on athletes running a marathon, other antennas can be mounted in door frames to read tags worn by people accessing a room or festival.
How do reader antennas work? In basic terms, a reader antenna converts electrical current into electromagnetic waves that are then radiated into space (similar to an FM radio) in a particular pattern at a given level of intensity. These radio waves can be received by a tag’s antenna and converted back to electrical current. The tag uses its own antenna to respond to send back a response (backscatter). When the tag responds, the reader antenna receives the information in a similar manner.
The parameters of greatest interest to the tag are polarization (or the reader antenna wave’s electric field vector, orientation, and direction) and the power level of the transmission. A linearly polarized antenna radiates entirely in one plane in the direction of signal propagation, while with a circularly polarized antenna, the plane of polarization rotates in a circular fashion (effectively a corkscrew when considered in time), making a complete revolution during one period of the wave.
