This chapter considers RFID label antennas for both near-?¬?eld operation in the HF region
and far-?¬?eld operation in the UHF frequency range. To aid in the development of UHF tag
antennas, the chapter contains material on the formulation of antenna equivalent circuits
and presents an RFID label antenna design methodology, illustrated in the far ?¬?eld with
the design of long-range, bow-tie antennas for tagging cases and pallets.
4.2 RFID Label Antennas
There are numerous label antenna designs, each with their own set of characteristics.
Antenna designs are in?¬‚uenced by a range of issues, such as the region of label operation
(near or far), the coupling ?¬?eld (electric ?¬?eld or magnetic ?¬?eld), the regulatory constraints,
and the environment in which they operate. For example, an environment with many
metal structures can affect time varying electromagnetic ?¬?elds, and thus affect the performance
of an antenna. Designing antennas to suit metallic structures requires special
consideration and is presented in Chapter 13 of this book. A number of examples of
antennas to suit their environment are outlined in Cole (2003), Pope et al. (1997), and
Ranasinghe et al. (2004). A vital aspect of the design process is to allow maximum coupling
between the reader antennas and label antennas for the coupling ?¬?eld used. Before considering
the subject matter of label antenna design, the following sections discuss a number
of different label antenna structures and the merits of their designs.
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