Energy harvesting technologies are required for autonomous applications, like sensors, for which a long‐time power sourcing from a battery is infeasible. An energy harvester converts different forms of environmental energy into electricity. It can replace, totally or partially, the batteries of certain micro‐systems that have low‐energy requirements. Therefore, the authors exploit the use of electromagnetic waves from broadcasters to power wireless sensors. The authors propose to realize harvesting operation at typical ambient radio frequency power levels found within urban environments. To explore the potential for ambient RF energy harvesting, an RF spectral survey was undertaken from outside in Paris. The average RF power in the frequency range 0.9–3 GHz is about −12 dBm. The harvester includes an antenna, an impedance‐matching network, and a rectifier; it was designed to cover two frequency bands from the largest RF contributors (GSM1800 and UMTS Band 1). A prototype is designed, fabricated, and measured. The RF‐to‐DC rectifier and the choice of the load to optimize the amount of DC power are presented. An efficiency of ∼45% was observed experimentally for the UMTS Band 1 and 33% for the GSM1800, whenever the incident power is −7 dBm. Numerical and experimental data are reported and discussed.

Abstract-This paper reports a 2.45 GHz, low power dual circularly polarized (DCP) and dual access rectenna. It contains two dc-recombined rectifiers and a cross-slot coupled square patch antenna fed by a microstrip line. A judicious dc recombination scheme allows to minimize the RF power imbalance between accesses caused by multipath effects and consequently arbitrary polarized incident waves. The proposed rectenna is then able to harvest linearly polarized, right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) electromagnetic waves, with nearly stable performances. The rectenna has been optimized at −15 dBm per access and dedicated to remote and contactless supply low consumption sensors. It has been experimentally tested with very low power densities from 0.057 µW/cm 2 (E rms = 0.46 V/m) to 2.3 µW/cm 2 (E rms = 2.95 V/m). At 1.49 µW/cm 2 (−15 dBm on each rectifier), the structure exhibits an output dc voltage and a global efficiency of 189 mV and 37.7%, respectively when the azimuthal angle (Φ) of the incident field is equal to 0 • . Due to the nearly constant total gain of the DCP antenna and an appropriate dc recombination of the two rectifiers, the global efficiency slightly varies between 37.7% and 41.4% when the azimuthal angle (Φ) varies between −90 and 90 • .

An efficient rectenna based on a dual Schottky diodes converter has been designed at 2.45 GHz. The proposed rectifying circuit is well suitable for wireless sensor applications because no input lowpass filter and no via-hole connections are required, resulting in a more simple structure. A simulation mixing an electromagnetic and circuit analysis has been first used to optimise the rectifier. In addition, the performances of the rectenna has been correctly predicted and characterised using an FDTD formulation extended to lumped circuit elements. The realised rectenna exhibits 83% efficiency over a 1050 V resistive load at a power density of 0.31 mW/cm 2 .Introduction: The rectenna is an important component for converting RF or microwave power into DC power. These techniques are of great interest to supply actuators [1] or wireless sensors [2] through free space without wire connections or a battery. A rectenna usually contains a receiving antenna, a combination of one or several Schottky diodes in series [3] or shunt [4], in voltage doubler configurations [5] or in a modified bridge converter [6], an input lowpass filter (LPF), an output DC pass filter and a resistive load. The input (LPF) rejects harmonics created by the diodes and provides matching between the antenna and the rectifier. It can be directly included on the radiating element by using harmonic-rejecting antennas [7].We propose an efficient rectenna design based on a dual diodes converter. In this configuration, the LPF between the antenna and diodes can be eliminated, reducing the insertion losses of the rectifier. The structure has been optimised and characterised using advanced design system (ADS) commercial software and the 3D-FDTD algorithm extended to lumped element circuits. Finally, simulated results are compared with the measured ones and show good agreement.

A compact and efficient rectenna based on a printed shorted annular ring-slot antenna with circular polarisation properties has been designed and evaluated at 2.45 GHz. The rectifier part is localised at the back side and centred inside the radiating element, resulting in a more compact structure in comparison with most conventional devices where rectifying circuit and antenna parts are geometrically clearly separated. In addition, the printed annular ring antenna is mismatched at the 4.9 GHz second and 7.35 GHz third harmonics, thus avoiding the use of an input lowpass filter. The proposed antenna and rectifier circuit have been first simulated and optimised separately using electromagnetic and circuit analyses, and then connected together. A maximum efficiency of 69% and an output DC voltage of 1.1 V have been measured over an optimised 2500 V resistive load at a power density of 20 mW/cm 2 . This rectenna is particularly suitable for powering wireless sensors or sensor networks by recycling ambient RF energy because it exhibits a global efficiency of more than 50% for power densities more than 10 mW/cm 2 .Introduction: Recently, most printed rectenna (rectifying antenna) circuits have been developed to supply wireless low consumption sensors or sensor nodes [1,2]. The rectenna is an essential device to capture ambient or controlled RF sources and convert this into useful electricity. To optimise the global efficiency and decrease the polarisation losses, antennas with circular polarisation (CP) properties are often preferred. Indeed, both efficiency and output DC voltage are relatively insensitive to the rectenna alignment in the azimuthal plane. Among the circularly polarised planar antennas studied earlier, it has been shown that the printed annular ring-slot antennas have good performances in terms of radiation properties [3]. When associated with a dedicated rectifier circuit, these constituted rectennas are particularly suitable for relatively low power densities as previously demonstrated at 2.45 and 5.8 GHz [4,5]. However, in these configurations and more generally, antenna and rectifier parts are separated in space resulting in a large rectenna area. We propose a novel rectenna design based on a circularly polarised annular ring-slot antenna and a zero bias serial Schottky diode converter dedicated for low power density applications (less than 20 mW/cm 2 ) [6]. In this configuration, the rectifier part is directly localised at the back side of the antenna, thus reducing the dimensions of the structure and the insertion losses of the rectifier. This makes the structure more compact and low cost.Antenna and rectifier were, respectively, designed with HFSS and Advanced Design System (ADS) commercial softwares. A coupling between Harmonic Balance and Momentum has been performed and is well suitable to accurately optimise rectenna designs [7]. Finally, measured results in term of axial ratio, global efficiency and output DC voltage are presented and discussed.

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