A Novel Isolation Technique for Closely Spaced PIFAs for UMTS Mobile Phones

In this letter, a novel port-to-port isolation technique suitable for a two-antenna system positioned at the top corner of a mobile phone is presented. The chosen planar inverted-F antennas (PIFAs) are intended to operate in the UMTS band [1.92-2.17] GHz and more precisely in the UMTS Rx band for diversity purpose. First, the distance between the PIFAs is severely reduced to 4 mm (0.027 lambda₀) in order to obtain a very compact system. This proximal placement causes an increase of the insertion loss between the feeding ports of the PIFAs and therefore degrades the overall diversity performance of the two-antenna system. To compensate for this effect, the neutralization technique previously proposed by the same authors is implemented. Then, a novel way to implement this technique is studied to further improve the PIFAs´ port-to-port isolation. It consists in achieving the neutralization of the antennas trough folded lines connected to the printed circuit board (PCB). A new prototype is fabricated and measured. The S-parameters and the total efficiency are presented. Additionally, the most important diversity metrics are computed to evaluate the potential of this novel two-antenna system for diversity applications in the UMTS Rx mode.