Figure 11 3D radiation pattern of the proposed fractal MPA array at (a) 5.35 GHz (b) 7.78 GHz (c) 9.47 GHz
SURFACE CURRENT DISTRIBUTION
To determine the influence of mutual coupling between the two array elements, Figure 12 (a-f) shows the current distribution at three resonant frequencies of 5.35 GHz, 7.78 GHz and 9.47 GHz. As shown in Figure 12 (a-f), the funnel-shaped stub and slotted ground plane decouples the energy from the fractal radiators and are mainly responsible for improving the isolation level between the two ports. This is also validated by the parametric analysis of the ground plane presented in Section 2. For port-1 excited by simulated 1W of power at the feed point (port-2 deactivated by 50 Ω load), the decoupling structure (inserted in the ground plane) allows a very small amount of current to flow through the non-activated port-2 for all three resonances. For activated port-2 and port-1 terminated, a similar reduction of coupling current is observed. Hence, the proposed fractal MPA array exhibits good isolation performance throughout the UWB of operation.