01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0
5
10
15
20
25
30
35
40
45
hB
Resistance ()
a = 5
a = 10
a = 30
a = 40
a = 50
a = 60
a = 90
FIGURE 4.21
RBr of bow-tie antennas of various ?¬‚are angles evaluated using the expressions in Table 4.5.
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
4000
3500
3000
2500
2000
1500
1000
500
0
500
hB
Reactance ()
a = 5
a = 10
a = 30
a = 40
a = 50
a = 60
a = 90
FIGURE 4.22
Reactance of bow-tie antennas of various ?¬‚are angles (from the expressions in Table 4.6).
84 RFID Handbook: Applications, Technology, Security, and Privacy
be designed starting with a more easily analyzed and understood antenna such as the
bow-tie antenna.
4.5.4 Bow-Tie Antenna with a Series Tuning Inductor
Considering an approximately credit card size, bow-tie antenna shows that the input
impedance is capacitive. This is true for any bow-tie antenna of <90 mm in height. We
must therefore seek a suitable matching circuit that can be built into the antenna to match
to an RFID chip??™s input impedance. The simplest possible matching circuit design, which is
simple to physically incorporate into the antenna, will generally provide the most suitable
antenna design.
Considering the equivalent circuit of the bow-tie antenna, it is possible to contemplate a
matching element as illustrated in Figure 4.
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