Reflector-Based Power Output Maximization and Near-Field Detuning-Mitigation in Miniaturized Tightly-Coupled Flexible Rectenna Arrays

Abstract

While rectenna arrays can improve the net DC output from low incident power densities, the effects of tight coupling and detuning are not typically explored. Here, the scalability of 915 MHz wire-type compact rectennas is investigated in terms of mutual coupling, DC output, and its immunity to near-field detuning. First, the mutual coupling between tightly-coupled dipole rectennas is investigated using s-parameters, showing a maximum coupling of 6 dB. The rectennas, achieving a 36% Power Conversion Efficiency (PCE) at −20 dBm, have been closely spaced forming a six-element array integrated with a radius of 7 cm. The effect of placing the omnidirectional rectennas on different dielectrics including lossy objects is investigated and a lightweight reflector-backing is proposed, demonstrating a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.3\times$</tex> higher power output at a low profile of 2 cm <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(0.06\lambda)$</tex> . The array is connected to a BQ25504 power management integrated circuits (PMIC), charging a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$100\mu \mathrm{F}$</tex> electrolytic capacitor in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$382\mathbf{s}$</tex> before powering a Bluetooth WSN for one successful advertisement at 0 dBm transmitted power, from a power density of O. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$22\ \mu \mathbf{W}/\mathbf{cm}^{2}$</tex> , with the potential for a three-fold improvement using an optimally-placed reflector.