A Simple Approach for Reducing Mutual Coupling in Two Closely Spaced Metamaterial-Inspired Monopole Antennas

A simple approach for reducing the mutual coupling in two closely spaced electrically small antennas (ESAs) is proposed based on the general idea of field cancellation. The antenna array consists of two metamaterial-inspired small printed monopole antennas. The mutual coupling is reduced by self-cancellation of the induced common ground and near-field currents, without introducing additional structures. A fabricated prototype of a two-element array with an edge-to-edge separation of ??₀/30.6 (or center-to-center separation of ??₀/13.6) yields a measured mutual coupling of |S₁₁| better than -18 dB across the impedance band of |S₁₁| < -10 dB, which is significantly better than the -9 dB level of the original array.