Millimeter-Wave Antennas: A Comprehensive State-of-the-Art Review of Design Approaches, Operating Bands, Challenges, and Applications in Body-Centric and Emerging Systems

This paper reviews and classifies more than 120 recent contributions on millimeter-wave (mm-wave) antennas, with emphasis on their operating bands, design methods, and application domains. It surveys the main mm-wave frequency ranges and their use in 5G/6G communications, radar and sensing, biomedical and body-centric systems, imaging, and radio-frequency energy harvesting and wireless power transfer. The review compares different antenna design approaches, including array and MIMO architectures, metasurface- and metamaterial-based structures, and integration-oriented solutions such as wearable platforms, outlining their typical trade-offs, implementation challenges, and limitations in terms of bandwidth, efficiency, miniaturization, and robustness. Particular attention is given to antennas operating in proximity to the human body, where performance is strongly influenced by tissue electromagnetic properties and safety constraints. In this context, the paper discusses design criteria based on Specific Absorption Rate (SAR) and Power Density (PD), as well as the role of physical, numerical, and voxel phantoms for accurate performance assessment and regulatory compliance. The review highlights practical use cases across these application areas and identifies open challenges and future research directions, including the exploitation of metasurfaces and Radio over fiber, to enable safe, efficient, and adaptive mm-wave antennas for emerging systems.