Design considerations for low antenna correlation and mutual coupling reduction in multi antenna terminals

The influence of mutual coupling on the envelope correlation between two identical planar inverted F-antennas (PIFA) are investigated. The capacity of a multiple-input multiple-output (MIMO) antenna system strongly depends on the correlation between the antennas. By placing two antennas in a fixed area, it is found that the envelope correlation could be halved simply by proper mutual orientation.

The set-ups that maximise the distances between the open ends of the PIFAs yield the lowest mutual coupling as well as the lowest envelope correlations. It is found that the envelope correlation is 0.8 when the PIFAs are oriented in parallel. The envelope correlation can be decreased to 0.4 by rotating one of the PIFAs by 180 degrees.