RF-ID 869Mhz Technology

869MHz RF-ID Technology

The new UHF 869.50MHz RFID frequency range has recently been released by ETSI for use in EUROPE and is significant for passive RFID tag technology because it gives longer read ranges than some other technologies. (Users in other countries outside Europe should check freq use) At Low frequencies - (less than 400MHz) the means of coupling is by Inductive Coupling. The magnetic component of the electromagnetic field is dominant. Power attenuates as the cube of the distance from the antenna and at the fourth and higher powers dependant upon Tag orientation and environmental conditions. Thus 13.56MHz series tags noteably have a short read range. At Higher Frequencies - At frequencies above 400MHz the means of coupling is by Propagation Coupling and the electrical component of the electromagnetic field is the dominant component, this results in a characteristic radio wave. Power attenuation is related to the square of the distance from the antenna, therefore higher frequencies with lower power radiated fields offer the promise of longer communication ranges.

RF Propagation Field

At UHF frequencies the radiated RF primary field and the reflected waves add constructively or destructively depending on path length differences, thereby causing nulls and peaks in the RF energy fields. In this example, at a certain instant in time, when a read command is issued by the fixed reader, the 3 red transponders cannot receive this command. With a fixed reader and a fixed output power stationary tags cannot always be read with 100% accuracy due to this phenomenen, but moving tags will move through troughs and peaks and so be identified. (As will tags with long enough antennae to span the troughs).The stationary tag problem can be overcome by sweeping the output power of the radiated RF field to move the peaks and troughs.This holds true for 2.4GHz range tags as well except that at the higher frequency means smaller troughs and peaks.

Radio Propagation


RF Propagation Field

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