MUTUAL COUPLING BETWEEN ANTENNA ELEMENTS
The miniaturization of antenna arrays imposes on the designer to place a large number of elements in a small footprint. This action gives rise to the so-called mutual coupling, which, in turn, causes crosstalk and distortion leading to the deterioration in the antenna performance and potential distortion of the radiation pattern. We won’t exaggerate if we say that such mutual coupling is the biggest obstacle to the miniaturization of antenna arrays. Over the years, antenna designers have found workarounds but with limited success. The workarounds include bandgap and ground defected structures as well as 3-dimensionncal vias.
THE MEANDER-LINE SOLUTION
Recently, a promising new decoupling technique has surfaced in the literature. It is called a micro-machined meander-line slot (ML). We use the popular EMWorks’ antenna software package, HFWorks to test the ML and study its decoupling efficiency.
Top and bottom view of 2×1 patch array antenna with ML slot
The meander line (ML) slots are inserted between the antenna patches on the bottom ground plane in order to suppress the surface currents.
S-parameters (S11 and S12) of the 2 × 1 patch array antenna with and without the ML slot: Port 1 is
excited, and Port 2 is terminated with 50 Ω
Electric field plot on the top plane for the above antennas without ML
Electric field plot on the top plane for the above antennas with ML
The results demonstrate that the ML is very efficient in reducing the coupling between antenna elements. Indeed, the S21 graphs clearly show that adding ML slots greatly improves the isolation between the antenna elements. Namely, S21, at 4.9 GHz is around 7.5 dB and 26 dB without and with the ML slots, respectively. In addition to the S-parameters, the near electric field plots on the top plane, shown above, also show a reduction in the coupling between the elements if a ML is used.
Hence, the ML is recommended to be used for reducing the coupling between elements in antenna arrays used in wireless communication, especially for 5G networks where the miniaturization is crucial.