The two different
structural designs presented have illustrated the antenna design process outlined in this
chapter and produced two successful RFID label antenna designs.
The discussion earlier clari?¬?es that RFID label antenna design limits the designer to
planar structures with inductive input impedance due to cost limitations and the nature of
the load impedance presented by an RFID chip. Consideration of an adequate size for an
antenna involves designing an antenna with an impedance that is a conjugate of the RFID
chip??™s input impedance.
Considering the subject of matching bandwidth, an interpretation of the Bode??“Fano
theorem provided a theoretical limit to the achievable power transfer to the RC load of an
RFID label IC. It has been observed that, in practice, if impedance matching is performed
over a certain bandwidth, there is a limit to the minimum achievable re?¬‚ection coef?¬?cient.
Thus for a given chip impedance (RC load), there is a compromise between the maximum
matching bandwidth and the maximum power transfer to the load.
The RFID label antennas presented in this section have many advantages. One of the
main advantages is the simplicity of the matching network. The bow-tie antenna required
only a simple matching network and both empirical and simulation methods were used in
designing that network. In addition, because of the small size of the antennas considered,
an excessively complex equivalent circuit for the antenna was not required.
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