Fig. 2 shows the design evolution of UWB antenna elements
with different feeding structures. Compared with the center-fed
printed antenna with a rhombic slot (denoted as Ant. 1), good
impedance matching over a wider frequency range can be
achieved by adopting an offset microstrip-fed line (denoted
as Ant. 2). This is due to the fact that the electromagnetic
coupling between the feed line and the ground improves as the