Chapter 3 - UHF RFID Antennas

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Chapter 3 - UHF RFID Antennas
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Figure 3.1 commercially UHF RFID tags
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Figure 3.2 Electric and magnetic fields around a
dipole antenna
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Figure 3.3 Simple circuit model of dipole antenna
near resonance
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Figure 3.4 Radiation pattern around a dipole
antenna
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Figure 3.5 Relationship between cylindrical and
ribbon dipoles
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Figure 3.6 Straight vs. meandering dipole
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Figure 3.7 commercial tip-loaded dipole tags
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Figure 3.8 Spiral-loaded tag
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Figure 3.9
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Figure 3.10
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Figure 3.11 Uda's circuit model of T-match
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Figure 3.12 Smith chart view of impedance
matching using the T-match
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Figure 3.13 Intuitive inductor-based circuit
model for the T-match
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Figure 3.14 New inductor-based circuit model of
the T-match dipole
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Figure 3.15 Transformed circuit model of RFID tag
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Figure 3.16 Meandering dipole used in the first
cut
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Figure 3.17 Circuit model of proposed antenna
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Figure 3.18 Return loss for circuit with f0 897
MHz, ß 0.165
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Figure 3.19 Return loss for circuit with f0 890
MHz, ß 0.17
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Figure 3.20 Circuit predicted impedance looking
into antenna
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Figure 3.21 Geometry of matching circuit
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Figure 3.22 Geometry of the completed antenna
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Figure 3.23 Return loss of circuit and simulated
antenna
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Figure 3.24 Radiation pattern of designed antenna
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Figure 3.25 Tag on semi-infinite dielectric
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Figure 3.26 Tag operating above a ground plane,
shown with image
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Figure 3.27 Impedance of a near-resonant dipole
above a 300 mm2 ground plane
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Figure 3.28 Microstrip antenna fed by a
microstrip transmission line
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Figure 3.29 Transmission line model of a
microstrip antenna
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Figure 3.30 Traditional unbalanced way to feed
the microstrip antenna
top
bottom
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Figure 3.31 Narrowband microstrip antenna
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Figure 3.32 Large, wideband microstrip antenna
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Figure 3.33 Impedance of variable length dipole
in free space (left) and 3.2 mm separation from
an infinite metal ground plane (right)
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Figure 3.34 Permissible region
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Figure 3.35 A prototype microstrip antenna
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Figure 3.36 A combined dipole / microstrip antenna
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Figure 3.37 Circuit model of combined dipole /
microstrip antenna functioning in air
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Figure 3.38 Circuit model of combined dipole /
microstrip antenna functioning on metal
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Figure 3.39 (a) dipole / microstrip antenna in
air
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Figure 3.39 (b) dipole / microstrip antenna on
metal
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Figure 3.40 (a) Power transfer efficiency of
combined dipole / microstrip antenna in air
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Figure 3.40 (b) Power transfer efficiency of
combined dipole / microstrip antenna on metal
(b).