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 demonstrate- 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.
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