Analysis of the Optimum Gain of a High-Pass L-Matching Network for Rectennas

Abstract

Rectennas, which mainly consist of an antenna, matching network, and rectifier, are used to harvest radiofrequency energy in order to power tiny sensor nodes, e.g., the nodes of the Internet of Things. This paper demonstrates for the first time, the existence of an optimum voltage gain for high-pass L-matching networks used in rectennas by deriving an analytical expression. The optimum gain is that which leads to maximum power efficiency of the rectenna. Here, apart from the L-matching network, a Schottky single-diode rectifier was used for the rectenna, which was optimized at 868 MHz for a power range from −30 dBm to −10 dBm. As the theoretical expression depends on parameters not very well-known a priori, an accurate search of the optimum gain for each power level was performed via simulations. Experimental results show remarkable power efficiencies ranging from 16% at −30 dBm to 55% at −10 dBm, which are for almost all the tested power levels the highest published in the literature for similar designs.

A High-Efficiency RF Harvester with Maximum Power Point Tracking

“…The rectenna transforms the RF signal to a dc voltage and the MPPT provides the optimum load to the rectenna in order to transfer maximum power to the sensor node. This paper continues and complements the work presented in [5] in two ways. First, the rectenna is fully characterized and modelled as a Thévenin equivalent circuit.…”

“…In Figure 4a, ηrect,max, VMPP,exp, and Voc,exp are also marked for Pav = −10 dBm. Achieved efficiencies (ηrect,max) are among the highest published in the literature for similar designs [5]. On the other hand, Voc (the Thévenin voltage) nearly matches Voc,exp.…”

“…The rectenna presented in [5] As for the FOCV-MPPT, a BQ25504 chip (Texas Instruments) was used, and in particular an evaluation board from the manufacturer. The chip contains a boost converter with PFM control and the board includes CL = 4.8 μF and Cload = 104.8 μF.…”

A Compact Thévenin Model for a Rectenna and Its Application to an RF Harvester with MPPT

“…Figure 2 shows the schematic circuit of the rectenna under study [33], which includes a high-pass L-matching network (composed of a capacitor C m and an inductor L m ), a half-wave rectifier, and an output filtering capacitor ( C o ). The antenna is modelled by a sinusoidal voltage source v a of amplitude V ap and frequency f o with a series radiation resistance R a .…”

“…The amplitude V ap is given by [12] as follows:Vap=22RaPav, where P av is the available power at the antenna. The matching network, at matching conditions, that is, Z m = R a (where Z m is defined in Figure 2), boosts the voltage at the input of the rectifier by a voltage gain, G t , given by [33] as follows:Gt=VinpVap=12(1+Q2), where V inp is the voltage amplitude of v in and Q is the circuit quality factor given by:Q=1ωoCmRa, where ω o = 2π f o . On the other hand, the value of L m must comply:Lm=1ωo21Cp+CmQ2/(1+Q2), where C p models the parasitic capacitance between node A and ground.…”