Design of Multi-Band Microstrip Rectenna Based on Characteristic Mode Analysis for Ambient RF Energy Harvesting
Srinivasan Vijay,
R. Ashok Bakkiyaraj and
Mohamed Mohamed Ismail
This paper presents a compact (80 × 80 mm2, approximately 0.66λ at 2.48 GHz) tri-band microstrip rectenna design guided by Characteristic Mode Analysis (CMA) for harvesting ambient RF energy. Modal significance characteristics are used to analyse both the fundamental and higher-order modes, and the required characteristic modes are tuned to the target bands by reshaping the surface current path so that the rectenna operates at S-band (2.48 GHz), 5G band (3.5 GHz), and C-band (4.7 GHz). An RF-to-DC rectifier, comprising an impedance matching network, two SMS7630-079LF Schottky diodes, a 100 pF DC-block capacitor, a low-pass filter, and a smoothing capacitor, is integrated on the same substrate as the multiband antenna. The antenna shows satisfactory impedance matching at its 50-Ω port and stable radiation performance, with fractional impedance bandwidths of 3.2%, 4.31%, and 2.57% at the three bands and a peak realized gain of 7.2 dBi over the operating range. At an input power of -30 dBm, harmonic-balance circuit simulation of the rectifier alone, driven by a 50-Ω source, predicts a peak RF-to-DC conversion efficiency of 52% into a 270 Ω load. Under ambient RF exposure, the fabricated rectenna delivers a measured DC output of 237.2 mV (0.208 mW) across the same load, corresponding to an area-normalized DC output power of approximately 32.5 mW/m2 over its 80 × 80 mm2 footprint. The incident RF power density at the aperture was not independently measured, so this result is reported as demonstrated DC output rather than measured conversion efficiency. These simulated and experimental results indicate that the proposed CMA-based rectenna is a promising candidate for self-powered IoT devices, wireless sensor networks, and other low-power autonomous electronics.
