A new method to increase the port-to-port isolation of a compact two-antenna UMTS system

In this paper, several compact systems with closed PIFAs (planar inverted-F antennas) positioned on the same PCB (printed-circuit board) of a mobile phone and operating in the UMTS band [1.92-2.17]GHz are presented. The proximal placement of the antennas causes an increase of the insertion loss between their feeding ports and therefore degrades the overall diversity performance even with the neutralization technique. Consequently, we propose a novel method to further minimize the port-to-port isolation. Initially separated by only a distance d=4 mm (0.027 lambda₀), we bring closer the antennas (d=2mm) to test the capabilities of the new method. Three prototypes (d=4mm, d=2mm and d=2mm with no neutralization) are fabricated and measured and their S-parameters compared. In addition, we estimate their diversity performance to get an idea of the potential of the new method for diversity and MIMO applications.