H., IEEE 2005 International Workshop onAntenna Technology: Small Antennas and Novel Metamaterials, NewYork,
USA, 2006, 2005 by IEEE. With permission.)
Reflection coefficient ??????
w (rad/s)
1
w 1 w 2
w
??????w
FIGURE 4.14
Theoretically possible minimum re?¬‚ection coef?¬?cient for the best
usage of p=RC over a bandwidth fromv1 to v2. (From Ranasinghe,
D.C., Leong, K.S., Ng, M.L., and Cole, P.H., IEEE 2005 International
Workshop on Antenna Technology: Small Antennas and Novel Metamaterials,
New York, USA, 2006, 2005 by IEEE.With permission.)
Far-Field Tag Antenna Design Methodology 73
Using the bandwidths outlined in Table 4.1, calculations of re?¬‚ection coef?¬?cient limit
established in Equation 4.2 are performed for the four regions: the United States, Europe,
Japan, Australia, and all of these regions simultaneously. The results are outlined in
Table 4.2. In the calculations, a chip resistance R of 1.3 kV and a chip capacitance C of
1.1 pF is assumed.
All the values for jGjDv therein are small. This implies that the allocated bandwidths for
RFID usage pose no theoretical limitations toward achieving a good impedance match to
the input impedance of the RFID IC.
However, recent advances in the fabrication of Schottky diodes and low-power CMOS
processes have yielded RFID chips with input chip impedance values where the resistance
R is about 2500 V with a parallel capacitance C of around 500 fF.
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