## 4 Parametric Study  
From the design, it is clear that the suggested wideband circularly polarized DRA is finalized in multiple steps. Thus, the final design depends on several parameters which affect the simulated results. These parameters include an air gap in the middle of the DR, a rectangular slot at the ground and a copper strip at the top of the DR. Some of these parameters effect both the reflection coefficient and axial ratio, while others affect either reflection coefficient or axial ratio alone. The first parametric analysis is performed for the air gap. Variations in the radius of the air gap change the reflection coefficients and impedance matching accordingly, while it has no significant effect on the axial ratios. Results of the air gap impact on the return loss is given in Figure 5. As evident in Figure 5, it can be clearly observed that increasing the air gap shifts the operating band to the right (higher range). The impedance matching of the operating band improves with the introduction of the air gap in the center of the DR. Thus, an air gap effects both the operating band and impedance matching. Based on the final simulated values, an air gap of 1.5 mm radius is finally selected. Figure 4: Axial ratios of the proposed design for the different design steps. Figure 3: Reflection coefficients for the different steps of the proposed design. Another important parameter is the ground slot. The effect of the ground slot on the reflection coefficient and axial ratio is illustrated in Figures 6 and 7, respectively. Figure 6 shows that in the absence of the ground slot the operating band is narrow and with relatively poor impedance matching at higher frequencies. Adding a ground slot with 2.3 mm slot width improves both the operating bandwidth and impedance matching. Further increase in the slot width slightly reduces the impedance matching. It is pertinent to mention that the variation in the ground slot width also slightly effects the axial ratio. Figure 7 shows this variation in detail. In the absence of the ground slot, the design is circularly polarized with poor axial ratio performance and axial ratio bandwidth. Adding the ground slot with 2.3 mm width improves both the axial ratio performance and axial ratio bandwidth. Increasing it further, the ground slot width further improves the axial ratio performance and axial ratio bandwidth. However, Figure 6 shows that at 3.5 mm width of the ground slot the impedance matching is decreased, but it is still considered a good value. Thus, at 3.5 mm width of the ground slot, the design has a good axial ratio bandwidth and performance with good operating band and impedance matching. Another important parameter is the stacked strip on the top of the DR. This important parameter mainly effects the axial ratio of the design while it has minimum effect on the reflection coefficient. Figure 8 depicts the effect of the increase or decrease in the copper strip length on the axial ratio. At 0.5 mm length of the strip, the axial ratio performance is better, but the axial ratio bandwidth is narrow. Slightly increasing the copper strip length to 1 mm slightly decreases the axial ratio performance but increases the axial ratio bandwidth. Any more increase in the strip length further reduces the axial ratio bandwidth but enhances the axial ratio performance. Any further increase in the strip width does not enhance the axial ratio bandwidth, while a degradation in axial ratio performance is noticed and therefore 1.5 mm length of the strip is finaliz  
Figure 5: Effect of changing the air gap radius on the Reflection Coefficient. The circular polarization characteristics of the proposed design are explained with the help of the electric field distribution on the top surface of the DR, which is shown in Figure 9. The corner feeding mechanism and the copper strip on the top of the DR collectively generate orthogonal modes in the DR. The electric field distribution of the proposed design is shown at 10.5 GHz.