Artificial Magnetic Conductor Frame to Improve Impedance Matching and Radiation Symmetry in 2$ imes$2 Array for 6G Applications

An Artificial Magnetic Conductor (AMC) frame capable of improving the impedance matching of a 2$\times$2 array for 6G applications without degrading isolation performance is presented. The proposed frame is integrated into the array without modifying the single radiating element design. By relying on accurate full-wave simulations, it results that the addition of the frame restores the impedance matching performance, achieving a bandwidth of 1.5 GHz at 28 GHz. The isolation between each port remains under -15 dB within the operating band, thanks to the vias in the rectangular patch metasurface. Moreover, the overall structure exhibits a gain of 11.81 dBi with an aperture efficiency of 69$%$, satisfactorily for broadband communication purposes. The proposed AMC frame represents an effective method for improving array performance without the need to alter the shape or dimensions of the single radiating element.

💡 Research Summary

The paper presents a novel Artificial Magnetic Conductor (AMC) frame designed to enhance the performance of a 2 × 2 dual‑polarized patch antenna array intended for 6G millimeter‑wave applications around 28 GHz. The authors start by highlighting a common problem: while a single dual‑polarized patch can provide wide bandwidth and high gain, assembling such elements into a compact array typically degrades impedance matching and introduces radiation pattern asymmetry due to strong mutual coupling. Traditional remedies—such as increasing substrate size or spacing—either compromise the array’s form factor or further deteriorate matching.

To address these issues without altering the original radiating element, the authors embed a rectangular metasurface (the AMC frame) around each patch. The metasurface is engineered to exhibit a near‑zero phase reflection (≈ 0°), mimicking an ideal magnetic conductor. Crucially, a set of metallic vias is placed at the center of each rectangular patch; these vias suppress surface currents that would otherwise flow between ports, thereby reducing inter‑element coupling. The AMC frame extends the original patch by only about 0.5 mm, preserving the overall footprint.

Full‑wave simulations performed with Simcenter Feko demonstrate that the AMC‑enhanced array restores the single‑element matching performance: S₁₁ and S₂₂ remain below –10 dB over a 1.5 GHz bandwidth centered at 28 GHz, whereas the same array without the frame shows a shifted resonance and poor matching. Isolation between any pair of the eight ports stays better than –15 dB across the operating band, confirming that the vias and AMC surface effectively mitigate mutual coupling.

Radiation characteristics also improve markedly. With the AMC frame, the array’s gain reaches 11.81 dBi, corresponding to an aperture efficiency of 69 %. The half‑power beamwidth (HPBW) is symmetric in both principal planes (≈ 65°), and cross‑polarization levels are suppressed to below –20 dB. In contrast, the array lacking the frame exhibits asymmetric beams (different HPBWs in the two planes) and higher side‑lobe levels.

The authors emphasize that the AMC frame can be applied as a post‑processing step to existing patch designs, avoiding redesign of the antenna geometry and reducing development time and cost. Its minimal size increase and low‑loss implementation make it suitable for dense massive‑MIMO, reconfigurable intelligent surface (RIS), and other 6G infrastructure where compactness, high gain, wide bandwidth, and strict isolation are simultaneously required.

In conclusion, the study validates that an AMC frame with strategically placed vias offers a practical, low‑overhead solution to the long‑standing trade‑off between array compactness and performance. By simultaneously restoring impedance matching, preserving high isolation, and ensuring symmetric high‑gain radiation, the proposed approach paves the way for scalable, high‑performance antenna arrays in forthcoming 6G networks.