User's Guide

CHAPTER 2 RFID OVERVIEW

Although an antenna may manifest its energy in a certain pattern, how your

system can use that energy depends on a great many factors including

antenna characteristics, tag and reader characteristics, the nature of the

items tagged, and the changing nature of the reading environment.

Polarization. Polarization of an antenna, expressed simply, means there is a

preferred orientation of the tag to the reader antenna’s energy field, which

may optimize the system’s ability to read tags, particularly under less than

ideal conditions. Under most normal conditions, and within the read range for

the system, all functioning tags should be readable. However, it may be

possible to read tags well beyond the specified read range if they are

oriented in the antenna’s preferred direction. Keep in mind, however, that

some systems may be designed to limit, rather than maximize, the read

range and thus may use polarization to facilitate tag discrimination.

Footprint Size and Read Range. The size of the antenna footprint and the

range at which a given tag may be read are affected, in various degrees, by

such factors as the output power of the transmitter, the receiver sensitivity,

the type of tag (and its own internal antenna) and the tag’s position relative to

the reader antenna. The reading environment also plays an important part in

determining how far out and where, in relation to the antenna, tags can and

cannot be read.

Because an antenna’s pattern is often irregularly shaped, you may get a read

at long range in one spot, then move the tag a few inches to one side and not

be able to get the tag to read again until you have moved it several feet

closer to the antenna.