Abstract— In this paper, a radio frequency energy harvesting rectenna system operating in the 915 MHz industrial scientific medical (ISM) band is designed and proposed. The proposed design – which consists of a flexible loop antenna, rectifier and matching section – has a small overall footprint area of 50×50 mm² (0.15λ₀ × 0.15λ₀) and achieves a power conversion efficiency of up to 80% for an input power of 5 dBm and load resistance of 20 kΩ. The system also demonstrates efficient performance, obtaining a high-power conversion efficiency of about 58% for a small input power of -15 dBm which represents an actual case of a small power captured from ambient resources. This is considered as the highest reported power conversion efficiency for a flexible energy harvesting system at 915 MHz with such a small size and an input power level of only -15 dBm. The proposed rectenna system has many appealing features, small size, flexibility, and relatively high-power conversion efficiency which make it a good candidate for energy harvesting applications.