Crescent-shaped double-monopole antennas with reduced coupling for WLAN and WIMAX applications

A double planar monopole antennas for WLAN and WiMAX application is proposed. Each antenna is represented in the form of crescent-shaped monopole structure. The lengths of the two arcs are designed to resonate at 2.45GHz, and 3.5GHz to meet the requirements for the WLAN and WiMAX standards respectively. The two monopoles have a small separation distance of 9mm (i.e., 0.0735λ₀ at 2.45GHz). A new technique is proposed for the reduction of the mutual coupling between two closely-spaced antennas by etching a slot in each of the feed lines of two the antennas. The slots are folded to the shape of the letter S to conserve length of the feedlines. In each antenna, the slot is tuned to resonate at the operating frequency of the other antenna so that the other frequency is notched out. The antenna performance was investigated by simulation using CST Microwave Studio software. The results show that the proposed method has reduced the envelope correlation coefficient by 35 folds at the 2.45 GHz, and 21 folds at the 3.5GHz frequency bands. Measured S-parameters verified the simulated results.