Port decoupling of two arbitrary antennas in close proximity through an Eigenmode feed network

This paper presents an alternative approach to decrease the mutual coupling between two arbitrary antennas. In this design, using a ring hybrid of arbitrary power division as the eigenmode feeding network, two arbitrary closely-spaced antennas can be decoupled. The input port matching can then be performed independently. A printed monopole antenna and a planar inverted F-antenna (PIFA) operating at 900MHz are considered, though two antennas of other types can be decoupled in the same manner. Decoupling of better than 25dB isolation is achieved between these two antennas at 900MHz when placed in close proximity.