20.
Far-Field Tag Antenna Design Methodology 81
FIGURE 4.17
A bow-tie antenna with the height hB and ?¬‚are angle a.
Vs
+
_ hB
Top plate
Flare angle a
Bottom plate
FIGURE 4.18
A three-parameter equivalent circuit model for a bow-tie antenna.
+
_
Vs
RBr
LB CB
FIGURE 4.19
Field con?¬?guration around a bow-tie antenna used for the calculation
of its self-capacitance.
82 RFID Handbook: Applications, Technology, Security, and Privacy
The model parameters outlined in Figure 4.18 will vary for different ?¬‚are angles and
heights of the bow-tie antenna, as is the case for a wedge above a ground plane antenna.
However, within the range of validity of the equivalent circuit, which depends on the
dimensions of the structure in relation to a wavelength, the radiation resistance, the
capacitance, and the inductance can be expected to scale up with increasing height for a
speci?¬?c ?¬‚are angle. The radiation resistance, the capacitance, and the inductance variation
for a bow-tie antenna can be summarized by the general expressions provided in Table 4.5,
where the height hB refers to the height of the bow-tie antennas as depicted in Figure 4.17.
In Table 4.5 the constants KBC and KBL are dimensionless quantities, whereas KBR is
measured in ohm. Table 4.5 is a summary of the parameters obtained for a bow-tie antenna
using the relationship between a bow-tie antenna and a wedge above a ground plane
antenna, using image theory based on the results from Brown and Woodward (1952), and
using our own experiments.
Pages:
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181