Figures 10 and 11 show simulated current distributions at 2.4 and 5.8 GHz. Current is concentrated on the microstrip line and around the slot. Also, a strong distribution at 2.4 GHz is concentrated near the right edge of the patch. Performance is strongly affected by the number and radii of slots and by microstrip feedline dimensions.

Figure 10

Figure 10 Antenna simulated surface current distribution at 2.4 GHz.

 

Figure 11

Figure 11 Antenna simulated surface current distribution at 5.8 GHz.

ANTENNA FABRICATION AND MEASUREMENTS

The dual-band RFID reader antenna is fabricated on a 1.5 mm FR4 substrate with a relative permittivity of 4.3 and a 0.025 loss tangent (see Figure 12). A network analyzer (see Figure 13) is used to measure |S11|. Measured and simulated results (see Figure 14) agree reasonably well across the operating band.

Figure 12

Figure 12 Fabricated antenna: front view (a) and back view (b).

 

Figure 13

Figure 13 Network analyzer measurement of antenna |S11|.

 

Figure 14

Figure 14 Comparison of antenna measured and simulated |S11|.

Figure 15 shows measured radiation patterns at 2.4 GHz. Note that the measured patterns are rotated by 90 degrees with respect to the simulated patterns in Figure 7. Similarly, measured radiation patterns at 5.8 GHz are shown in Figure 16, rotated by 90 degrees with respect to the simulated pattern in Figure 8.

Figure 15

Figure 15 Measured 2.4 GHz E- and H-Plane radiation patterns (blue solid line is H-Plane, red dotted line is E-Plane).

 

F16

Figure 16 Measured 5.8 GHz E- and H-Plane radiation pattern (black solid line is H-Plane, blue dotted line is E-Plane).

CONCLUSIONS

Table III compares these results with similar recently published work. This antenna has comparable dimensions, impedance bandwidth and gain values. Good characteristics are achieved using the slots technique. The slots are introduced along the length of the radiating element to reduce antenna dimensions, to achieve dual-band performance and to improve return loss and gain. This antenna is easy to physically realize as a one port dual-band RFID reader antenna.

Table 3

Table 3 Comparison with other work

References

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