18). The radiation pattern of the dipole
antenna allows the tag to intercept most of the incident signal regardless of the tag
orientation with respect to the reader??™s antenna, where a dipole antenna typically has a
gain of about 2.2 dBi. In addition, the RFID readers are designed to operate with the patch
(directional) type antennas. Thus, the power of radiated signal is focused toward a passive
tag. The antenna manufacturers normally specify the antenna gain for the circularly
polarized patch antennas to be on the order of 6 dBi.
1.4 Summary
The successful operation of a passive RFID system is dependent on numerous factors most
of which are interrelated and incorporated in the Friis equation of Figure 1.1. The typical
hands on manipulation of tags in the presence of a reader involves various factors
illustrated in this chapter. Such manipulation simultaneously varies multiple factors that
FIGURE 1.19
The isotropic radiation pattern.
14 RFID Handbook: Applications, Technology, Security, and Privacy
can only be separated by an in-depth analysis of the physical factors of the tag and reader
design. In addition, the multiple orientations and distances increase the dimensionality of
the problem.
A successful read or nonread is an amalgamation of these many factors. One means of
separating these factors is a well-documented testing procedure, providing a geometric
positional log in conjunction with a real-time spectrum analyzer that can monitor the air
medium and document the reader to tag energy pro?¬?le and the tag to reader backscatter.
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