A compact fractal-based reconfigurable antenna for millimeter-wave radio frequency energy harvesting in low-power internet of things devices

This paper presents the design and performance evaluation of a compact hybrid fractal-based reconfigurable microstrip antenna optimized for millimeter-wave (mmWave) RF energy harvesting in low-power Internet of Things (IoT) applications. The proposed antenna employs a Minkowski–Sierpinski hybrid fractal geometry implemented on a Rogers RT/duroid 5880 substrate to achieve miniaturization, wideband operation, and enhanced radiation performance within the 25–35 GHz frequency range. Frequency reconfigurability is introduced using strategically positioned PIN diodes, enabling dynamic tuning across multiple mmWave sub-bands to adapt to varying ambient RF conditions. The proposed design demonstrates the potential for RF energy harvesting in IoT applications based on simulation and analytical evaluation.. The antenna design was developed and analyzed using ANSYS HFSS full-wave electromagnetic simulations. Performance metrics including reflection coefficient (S _{1 1} ), voltage standing wave ratio (VSWR), gain, and radiation characteristics were evaluated for multiple switching configurations. The proposed design achieves a reflection coefficient below −14 dB, VSWR less than 2 across the operational band, and a peak gain of 5.1 dBi, demonstrating strong impedance matching and stable radiation behavior. The hybrid fractal configuration improves current distribution, enhances effective electrical length, and supports multiband resonance without increasing physical dimensions. Furthermore, the antenna's reconfigurable capability enhances RF energy capture efficiency in dynamically varying 5G environments, making it suitable for self-powered IoT sensor nodes. The proposed design establishes a scalable framework for compact, energy-aware, and frequency-agile antenna systems supporting next-generation sustainable wireless networks.