An efficient method is proposed to significantly reduce the near field coupling
between elements in a communication antenna array. The idea is based on exiting
a current flow through appropriate conductive path between adjacent antennas.
The conductive paths are designed and optimized in such a way that the feedforward
current (from the conducting path) on the adjacent antenna is
approximately equal in magnitude and out-of phase with the induced current on
the same antenna due to the near field coupling. Effectively when the deriving
antenna element is excited, the total power received at the input matched terminal
of the other antenna is reduced remarkably over the entire bandwidth of operation.
As the coupling level decreases, the radiation pattern of the deriving antenna
element, in the presence of the other antenna tends to be more similar to that of
the antenna in isolation. This way each omnidirectional antenna element in an
array, if all such mutual couplings is effectively reduced, can observe the waves
that are arriving from different directions. Without such provision, the pattern of
an antenna element, due to scattering and coupling from other array elements,
become directional and therefore the performance of the multiple antenna array
degrades. After demonstrating the near-field coupling cancellation approach for
two antennas, the method is extended to a circular array where only feed-forward
path is applied to circumferentially adjacent elements. It is shown that, the
scattering effects of the other antennas on the radiation pattern of each individual
antenna cannot be completely eliminated but can be kept below an acceptable
level by the proposed technique. By virtue of this method for reducing the mutual
coupling, the overall array has the capability to create more directive radiation
pattern with lower side-lobes. This technique is utilized to reduce the coupling
between biconical antennas in a circular array within 40% bandwidth. It is
demonstrated that there is an optimum magnitude and phase weighting for the
array with reduced mutual couplings for which the radiation pattern exhibits
higher gain and less side-lobe levels compared to the one with higher level of
coupling between elements.