Harmonic interference suppression within a multiple‐antenna system using integrated slender magnetic metamaterials

In a multiple‐antenna system, harmonics of lower‐frequency antennas will interfere with higher‐frequency antennas, especially when the latter operates around the harmonic frequencies of the former. In this communication, we propose to suppress harmonic interferences in multiple‐antenna systems using integrated magnetic metamaterials (MM). To this end, we firstly designed a slender MM suitable for integration. Interdigital capacitor is adopted to make the MM slender enough to accommodate itself within the narrow gap between antennas. When magnetic field lines thread through the MM, negative permeability can be achieved due to strong magnetic resonance, which will block harmonic magnetic fields of an antenna penetrating into its neighbors. As an example, we investigated a dual patch‐antenna system, where the smaller one operates at the second‐harmonic frequency of the larger one and the MM is integrated in the gap between them. By adjusting structural parameters, the second‐harmonic magnetic fields of the larger antenna are blocked from penetrating into the smaller antenna. In this way, harmonic interferences within the antenna system can be suppressed. A prototype, together with a reference sample, was fabricated and measured. Both the measured and simulated results verify that with the MM, the harmonic coupling is reduced down to below −20 dB even when the gap between the two antennas is only about 0.06λ. Compared with the reference sample, the harmonic coupling is reduced by more than 7 dB. This work provides an alternative method of reducing harmonic interferences within multiple‐antenna systems to enhance the electromagnetic compatibility.