Design of a square ring shape slot antenna for UWB polarization–diversity applications

In this paper, a dual polarized slot antenna for ultra wideband applications is proposed. The slot has an overall shape of a square ring whose four arms are identical and stepped rectangular. While two adjacent arms of the ring are microstrip fed and are responsible for the orthogonally polarized fields, the other two arms are introduced to make the structure symmetric and reduce the cross polarization. The impedance matching and isolation are controlled by properly shaping the slot arms and the feed section and by insertion of several narrow metallic and slot stubs. The measured impedance bandwidth is 116% (from 3.2 GHz to 12.0 GHz) for both the ports. The isolation is better than 20 dB from 4.4 GHz onwards. With the help of radiation patterns and electric field distribution inside the slot, the dual polarized nature of the antenna is justified. A modified design having measured isolation of 18 dB from 3.5 GHz onwards is also presented. With compact features, huge impedance bandwidth, good isolation and acceptable cross polar levels along the boresight direction, the antenna is expected to be useful for UWB transmission incorporating MIMO, radar and medical imaging applications.