Enhanced Bandwidth of Small Square Monopole Antenna by using Inverted U-shaped Slot and Conductor-Backed Plane

This paper, presents a novel multi-resonance monopole antenna for ultra wideband applications. The proposed antenna consists of a square radiating patch with an inverted U-shaped slot and a ground plane with an inverted U-shaped conductor-backed plane, which leads to a wide usable fractional bandwidth of more than 135% (2.9-15.1 GHz). By cutting a modified inverted U-shaped slot with variable dimensions on the radiating patch and also by inserting an inverted U-shaped conductor-backed plane, additional resonances are excited and hence much wider impedance bandwidth can be produced, especially at the higher band. The designed antenna has a small size of 12x18 mm(2), or about 0.15 lambda x 0.25 lambda at 4.2 GHz (the first resonance frequency). Simulated and experimental results obtained for this antenna show that it exhibits good radiation behavior within the UWB frequency range.