Characteristic Mode Aided Design of Handset Antennas with High Isolations

The public frequency spectrum of 2.4-2.485 GHz is shared by WLAN, Bluetooth, Micro-oven and etc. When multiple functions are integrated in one device, the isolations between antennas should be as high as possible for mutual interference. In this work, a dual-antenna system in the mobile handset working at 2.4-2.485 GHz is designed with high isolations so that they can work for different communication protocols with less requirement on the filter. The two antennas are designed on the top half of the handset to save more space for other antennas. Given the position of the first antenna, the feeding position of the second antenna is calculated based on characteristic mode theory. According to the full-wave simulation results, an isolation of above 40 dB has been achieved. The correlation coefficient is 0.03 at 2.4 GHz.