Reconfigurable Antennas for 5G/6G, IoT, and Medical Applications : A Comprehensive Review of Enabling Technologies, Design Techniques, and Emerging Trends

Reconfigurable antennas have emerged as a key enabling technology for smart and adaptive wireless communication systems, offering dynamic control of radiation characteristics to meet the evolving demands of modern networks such as 4G, 5G, and emerging 6G systems. This paper presents a comprehensive review of reconfigurable antenna technologies with emphasis on switching mechanisms, including PIN diodes, RF MEMS, and varactor diodes, which enable tuning of frequency, radiation pattern, polarization, and impedance characteristics through controlled current distribution on the radiating element. However, the integration of active switching components introduces challenges such as increased design complexity, biasing network requirements, and cost implications. The review highlights that most existing works focus on microstrip patch-based configurations integrated with switching circuits, making them suitable for compact wireless terminals and advanced applications, including IoT, satellite communications, and biomedical systems. In particular, medical and biomedical applications benefit significantly from reconfigurable antennas in body-centric wireless communication systems, wearable health monitoring devices, implantable sensors, and wireless medical telemetry, where compact size, low power operation, polarization diversity, and reduced Specific Absorption Rate (SAR) are critical requirements. In terms of operating bands, S-band (2-4 GHz) dominates reported designs (35.5%), followed by C-band (4-8 GHz) (27.6%), reflecting their suitability for practical wireless systems. Frequency reconfiguration remains the most widely adopted mode (approximately 70%), while electrical reconfiguration using PIN diodes is the predominant technique (about 72.5%) due to its simplicity and effectiveness. Additionally, recent advancements in metasurface-based reconfigurable antennas and their integration with MIMO systems are enabling enhanced performance in terms of gain, isolation, and spectral efficiency for next-generation 5G/6G wireless networks. This paper systematically categorizes reconfiguration techniques, switching technologies, frequency bands, and application domains, including biomedical and medical applications, providing a clear overview of current trends and future research directions in reconfigurable antenna design.