Yeong-Nan Phua0000-0001-5301-1115Eng-Hock Lim0000-0001-8262-5693Boon Kuan Chung2026-10-202026-10-202025-08-0710.1080/03772063.2025.2542537https://dspace-cris.utar.edu.my/handle/123456789/11806A broadband reflectarray that is designed using two closely coupled inter-layer ring-patches is investigated for the first time. The two patches are tactfully stacked on the top and bottom surfaces of a substrate to achieve an enhanced bandwidth of reflectarray. Due to the tight coupling between the inter-layer patches, the coupling between the neighbouring reflectarray elements can be significantly minimized. Here, the S-curve is generated in a unique way from a geometry-phase relationship equation that is linked to the geometrical parameters of the ring-patches. A linear and broad phase range of 527o with a low reflection loss of < 1 dB is achievable. In addition, a phase optimization scheme involving a cost function has been employed for optimizing the S-curve, making it smooth and linear over a large bandwidth with low reflection loss. A 13 × 13 reflectarray with a square aperture has been designed and demonstrated. Measurement results show that an antenna gain of 23.6 dBi with a wide -1-dB gain bandwidth of 33.2% is achievable. The proposed reflectarray has an aperture efficiency of 43.8% with a low cross-polarization level of < -30 dB. © 2025 IETE.en-USCircular ring-patchInter-layer couplingReflectarrayUnit cellAntennasCost functionsCurve fittingGeometryBroadband reflectarrayCircular ringInter-layersReflectarraysReflection lossS CurveTop surfaceUnit cellsBandwidthjournal-article