Design and Validation of an Ultra-Wideband Log Spiral Antenna for RF Energy Harvesting

Abstract

This paper presents the design, simulation, fabrication, and validation of an ultra-wideband (UWB) log spiral antenna engineered for radio frequency (RF) energy harvesting over 500 MHz–3 GHz. The antenna addresses traditional limitations of log-spiral designs, including rapid physical expansion and challenges in achieving low cut-off frequencies. Using CST Studio Suite 2025, the antenna was modelled with optimized geometric parameters derived from analytical equations, enabling compactness while preserving wideband characteristics. Performance evaluations—including return loss (S11), voltage standing wave ratio (VSWR), gain, radiation pattern, and far-field behavior—were conducted. Fabrication was completed using FR4 substrate followed by measurement using a FieldFox vector network analyzer and anechoic chamber. Results demonstrate excellent agreement between simulation and physical measurements, achieving −20.9 dB (simulated) and −32 dB (measured) return loss, and VSWR values near unity (1.06–1.19). The antenna exhibits suitable omnidirectional radiation and efficiencies required for broadband RF energy harvesting. This work confirms the feasibility of developing low-cost, planar, wideband spiral antennas for ambient RF energy capture and provides a practical foundation for integration with rectifying circuits in low-power IoT systems.