Flexible Antennas for 6G Communication and Harsh Environments: Design, Materials, Fabrication, Testing, and AI/ML Integration

Sixth-generation (6G) wireless communication systems impose stringent requirements on antenna performance, including ultra-high data rates, ultra-lowlatency, massive connectivity, high-frequency operation, advanced beamforming, and long-term reliability. Achieving these goals at mm-wave and sub-terahertz frequencies introduces major challenges such as severe path loss, hardware complexity, thermal stress, limited flexibility, and performance degradation under mechanical and environmental variations. This review presents a comprehensive overview of 6G antenna requirements, key antenna technologies, material platforms, fabrication techniques, AI/ML integration, and reliability assessment. Advanced antenna solutions, including hybrid antenna arrays, antenna collocation, metasurfaces and reconfigurable intelligent surfaces, and mm-wave and terahertz antennas are discussed alongside their limitations in flexibility and robustness. Flexible antennas are highlighted as a promising solution, enabled by emerging materials and additive fabrication methods such as inkjet printing, aerosol jet printing, screen printing, and additive manufacturing. In addition, standardized testing and reliability evaluation under harsh environments, such as bending, thermal cycling, humidity, and aging are reviewed. Finally, the integration of artificial intelligence and machine learning for antenna design optimization, fabrication control, and performance enhancement is discussed, outlining future directions for reliable and scalable 6G antenna systems.