Simulations of |S11| and AR with key parameters of different dimensions are plotted in Figures 6 through 8. Many references have pointed out that the elongated feed is an important factor affecting impedance matching. As seen in Figure 6, the optimum dimension produces the widest impedance bandwidth and ARBW. Figure 7 shows the effect of the meander line location on |S11| and AR. |S11| changes slightly, but with an optimum location, the widest ARBW is achieved. Finally, Figure 8 shows the effect of the L0 dimension. The results clearly indicate that it has a great effect on the impedance bandwidth and ARBW. As the size of L0 becomes larger, the impedance and AR bandwidths become wider. However, due to the limitation of the distance between the meander line and the asymmetrical ground, its length is set as 8 mm.

Figure 8

Figure 8 Simulated |S11| and AR with different L0.

Figure 9

Figure 9 Simulated versus measured results.

EXPERIMENTAL RESULTS

Table 2

Simulated and measured results are shown in Figure 9. The simulated –10 dB impedance bandwidth is 4.52 GHz (2.12 to 6.64 GHz) and the ARBW is 3.17 GHz (2.82 to 5.99 GHz). For comparison, the measured impedance bandwidth is 4.65 GHz (2.10 to 6.75 GHz) and the ARBW is 3.40 GHz (2.65 to 6.05 GHz). The results are consistent with the simulation. Slight discrepancies are mainly due to material, measurement uncertainties and fabrication tolerances. These results show that the antenna has advantages in structure and bandwidth compared with those represented in the referenced work of Table 2.

Figure 10 shows that the antenna’s gain is higher than 3.8 dBic within the CP bandwidth with a maximum gain of 7.8 dBic. The radiation efficiency is a maximum of 96 percent occurring at 4.1 GHz.

Simulated versus measured radiation patterns in the xoz- and yoz-planes at 5 GHz (see Figure 11) are bi-directional and in close agreement. Simulated results in ADS agree closely with those in HFSS as well.

Figure 10

Figure 10 Antenna gain and radiation efficiency.

Figure 11

Figure 11 Radiation patterns at 5 GHz: xoz (a) and yoz (b).

CONCLUSION

A novel asymmetrical CPW-fed antenna with broadband circular polarization uses an asymmetrical ground and meander line to achieve circular polarization and improved bandwidth. After parameter optimization, the measured -10 dB impedance bandwidth is 103.2 percent (from 2.12 to 6.64 GHz) and the ARBW is 72.0 percent (from 2.82 to 5.99 GHz), which agrees well with the simulations. With a simple structure, wide ARBW and low profile, this antenna is suitable for many applications in modern communication systems.

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