Objective To address the challenges of high propagation loss and susceptibility to blockage in 5G millimeter-wave communications, coupled with the constraints of limited space and curved surface installations on ships‒and considering the drawbacks of traditional high-frequency rigid substrates such as high cost and insufficient flexibility‒this paper proposes a 28/38 GHz dual-band four-port MIMO antenna based on a photo paper-based flexible substrate. By integrating low-cost, degradable materials with a high-isolation structural design, the proposed antenna achieves compact dimensions and favorable radiation performance, making it suitable for millimeter-wave communication in complex shipboard environments.

Method The design utilizes a coplanar waveguide (CPW)-fed cross-shaped monopole radiating element. By introducing a narrow slot at the center of the radiating patch and etching symmetrical rectangular slots in the ground plane, dual-band resonance at 28 GHz and 38 GHz is achieved. A four-port 2×2 centrally symmetric MIMO array is then constructed to enhance spatial diversity and mitigate inherent coupling. Additionally, a cross-shaped decoupling stub is introduced at the center of the array, which generates an out-of-phase coupling path to neutralize mutual coupling, thereby suppressing near-field coupling between elements from an electromagnetic mechanism perspective. The overall dimensions of the antenna are 25 mm × 40 mm × 0.27 mm, and a prototype is fabricated using a screen-printed copper paste process. Its performance is validated through surface current distribution analysis, parametric studies, and bending tests.

Results Measurement results indicate that the antenna achieves good impedance matching (S11 < −10 dB) in both the 28 GHz and 38 GHz bands, with operating bandwidths of 26.25～29.26 GHz and 37.2～39 GHz, respectively. Owing to the introduction of the cross-shaped decoupling stub, the isolation between the four ports exceeds −32 dB across the entire operating band, representing an improvement of approximately 4 dB compared to the structure without the stub. MIMO performance metrics show an envelope correlation coefficient (ECC) of less than 0.004 and a diversity gain (DG) exceeding 9.999 dB. The antenna exhibits radiation efficiency above 80% in both frequency bands, with peak gains of 4.3 dBi and 3.8 dBi, respectively. Under bending conditions with radii ranging from 30 mm to 50 mm, the antenna maintains stable dual-band operation.

Conclusion The proposed antenna achieves dual-band, high-isolation MIMO performance within a compact structure while offering flexibility, lightweight construction, and environmental sustainability. It meets the demands for high-capacity and reliable millimeter-wave communication in complex environments such as ships, thereby providing a new technical pathway for the development of green electronics and sustainable communication devices.