Coupling minimisation between RH and LH/RH curl antennas positioned over a ground plane

Two printed curl antennas operating above a ground plane and each of opposite polarisations are deployed for transceiver use. It is found that, in most instances, the mutual coupling between the curl antennas of the opposite hand of circular polarisation is greater in comparison than the coupling between curl antennas of the same hand of circular polarisation. The effect which when measured, generally results, in inferior performance for a RHCP/LHCP arrangement than for a RHCP/RHCP arrangement. The purpose of this paper is to provide an examination of the current distributions along each of the curl antennas in order to provide a rationale as to why this is occurring. A recommendation is also given on the relative angular orientations between antennas of opposite polarisation hands in order to reduce the mutual coupling between them from -15 dB to -25 dB or for same hand polarisation to -35 dB at lambda/2 spacing.