Design of a Compact Ground-Slotted Dual-Band Microstrip Antenna for Ambient RF Energy Harvesting

Rapid technological advancements and the growing use of electronic devices have increased the demand for electrical energy. In this regard, radio frequency (RF) energy harvesting offers an environmentally friendly and cost-effective solution by capturing ambient electromagnetic waves using specially designed antennas. In this study, a compact dual-band microstrip patch antenna operating at 1.75 GHz (GSM-1800 uplink) and 2.45 GHz (Wi-Fi band) was designed on an FR-4 substrate with dimensions of 40 × 47 × 1.6 mm3 (0.23λ × 0.27λ × 0.0093λ at 1.75 GHz). A rectangular slot etched in the ground plane introduces a lower resonance in addition to the fundamental patch mode, and its geometry was optimized using the parametric sweep feature of CST Microwave Studio. An analytical link-budget model relating the incident electric field and the antenna characteristics to the RF power delivered to the harvester was formulated and used to interpret the measurements. The fabricated antenna exhibits measured −10 dB bands that contain both target channels, while peak realized gains of 1.07 dBi and 2.54 dBi and total efficiencies of 68% and 83% were obtained in simulation; the radiation characteristics of the prototype were not measured. Under controlled short-range illumination, the RF power received by the antenna exceeded the minimum input power of a P21XXCSR-EVB harvester, which was activated in both bands, and DC voltages of 3.60 V and 3.85 V were read at its output at 1.75 GHz and 2.45 GHz, respectively. With the simulated gains and under ideal polarization alignment and matching, the analysis gives lower-bound plane-wave-equivalent fields of about 2.5 V/m and 3.3 V/m for reaching the minimum input power of the harvester; such levels generally occur only close to a transmitter. The proposed antenna is therefore a suitable compact receiving element for low-power IoT harvesting systems that operate in sufficiently strong RF fields or employ a rectifier of adequate sensitivity, whereas wearable use remains a possible application that has not been evaluated here.