Toward Electromagnetic Near-field Mutual Coupling Suppression with Active Janus Sources

In recent years, the characteristics of radiation sources have been extensively studied. Amongst them, the Huygens source, constructed by the orthogonal electric and magnetic dipoles which radiate in phase, has made significant contributions to the fields of metasurfaces and antennas due to its unidirectional far-field radiation property. The Janus source, constructed by the same dipoles radiating 90◦ out of phase, is shown to have a strong directional preference in near-field power coupling [1]. This makes it, in some sense, a near-field equivalent to the Huygens source, and potentially very useful in engineering the near-fields of metasurfaces and antenna systems. However, the robust generation of the Janus source and an investigation of power coupling with an active realistic Janus source remains heretofore unreported, which limits the potential application scenarios.

In this work, we propose the active Janus and Huygens sources to investigate the directional properties of their EM fields. We use a twin current filament model to construct active Janus and Huygens sources [2]. Simulation of this source in a parallel plate waveguide (PPW) environment shows that the Janus and Huygens sources achieve similar far-field performance as their equivalents in 3D space. Investigations in the near-field show the PPW sources possess directive coupling properties in agreement with earlier works featuring ideal Janus and Huygens sources [3].

Then we show that the near-field directionality of the Janus source can be applied to suppress mutual coupling between two active Janus sources. We show, in simulation, the generation of the active Janus source using a twin current filament within a parallel plate waveguide. Then, by placing two Janus sources with reversed directionality near one another, we demonstrate, in full-wave simulation, that mutual coupling between two such sources can be suppressed around 1000-fold when the center-to-center separation distance changes from 0.12 to 0.24 wavelengths at 800 MHz. Such strong suppression of mutual coupling between deep sub-wavelength spaced, quasi-isotropic sources can find very attractive applications in compact MIMO communication systems.