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. 2021 May 4;21(9):3193.
doi: 10.3390/s21093193.

Compact Antenna in 3D Configuration for Rectenna Wireless Power Transmission Applications

Alassane Sidibe  1   2 , Alexandru Takacs  1 , Gaël Loubet  1 , Daniela Dragomirescu  1
Affiliations

Compact Antenna in 3D Configuration for Rectenna Wireless Power Transmission Applications

Alassane Sidibe et al. Sensors (Basel). .

Abstract

This work presents methods for miniaturizing and characterizing a modified dipole antenna dedicated to the implementation of wireless power transmission systems. The antenna size should respect the planar dimensions of 60 mm × 30 mm to be integrated with small IoT devices such as a Bluetooth Lower Energy Sensing Node. The provided design is based on a folded short-circuited dipole antenna, also named a T-match antenna. Faced with the difficulty of reducing the physical dimensions of the antenna, we propose a 3D configuration by adding vertical metallic arms on the edges of the antenna. The adopted 3D design has an overall size of 56 mm × 32 mm × 10 mm at 868 MHz. Three antenna-feeding techniques were evaluated to characterize this antenna. They consist of soldering a U.FL connector on the input port; vertically connecting a tapered balun to the antenna; and integrating a microstrip transition to the layer of the antenna. The experimental results of the selected feeding techniques show good agreements and the antenna has a maximum gain of +1.54 dBi in the elevation plane (E-plane). In addition, a final modification was operated to the designed antenna to have a more compact structure with a size of 40 mm × 30 mm × 10 mm at 868 MHz. Such modification reduces the radiation surface of the antenna and so the antenna gain and bandwidth. This antenna can achieve a maximum gain of +1.1 dBi in the E-plane. The two antennas proposed in this paper were then associated with a rectifier to perform energy harvesting for powering Bluetooth Low Energy wireless sensors. The measured RF-DC (radiofrequency to direct current) conversion efficiency is 73.88% (first design) and 60.21% (second design) with an illuminating power density of 3.1 µW/cm2 at 868 MHz with a 10 kΩ load resistor.

Keywords: compact antenna; energy harvesting; rectenna; wireless power transmission (WPT); wireless sensors.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Conventional dipole antenna simulated on the required size dimensions. (a) The input impedance representation on Smith chart; (b) Half-wavelength antenna dimensions; (c) Simulated 3D radiation pattern at 2 GHz.
Figure 2
Figure 2
Detailed geometry of the compact, T-match dipole antenna on an FR4 substrate (Lsub = 56 mm, Wsub = 32 mm, L1 = 20.65 mm, W1 = 5.95 mm, L2 = 16.8 mm, W2 = 10.5 mm, L3 = 14 mm, W3 = 9.625 mm, E1 = 0.35 mm, E2 = 1.05 mm, g = 2.03 mm).
Figure 3
Figure 3
Evolution of the input impedance (Real and Imaginary parts) as function of the frequency with various shorting line width (W) values.
Figure 4
Figure 4
Simulated S11 (return loss) of the antenna for different configurations; L = 10 mm (black), L = 30 mm (blue) and L = 51.4 mm (red).
Figure 5
Figure 5
(a) Geometry of the 3D configuration antenna with the connected metallic arms; (b) Simulated 3D gain polar plot at 868 MHz.
Figure 6
Figure 6
Designed antennas on HFSS: (a) The first miniaturized antenna and the second miniaturized antenna named A2: 3D FDA; (b) 3D polar plot of the radiation pattern of A2 antenna at the resonant frequency (HFSS results).
Figure 7
Figure 7
Radiation pattern on the E-plane and H-plane at 868 MHz. (a) The antenna first 3D dipole antenna in Section 2.1; (b) The modified 3D dipole antenna (A2).
Figure 8
Figure 8
(a) Antenna with a U.FL connector named AC; (b) Antenna with connected tapered balun named ATB; (c) Antenna with integrated microstrip transition named AIT.
Figure 9
Figure 9
Comparison of the measured return loss (S11) of the D1 antenna with different feeding methods.
Figure 10
Figure 10
Measured and simulated reflection coefficient of the A1 and A2 antennas.
Figure 11
Figure 11
Simulated (dashed line) and measured (continuous line) radiation pattern (gain plot in the E-plane): (a) AC antenna; (b) A2 antenna at the resonant frequency (868 MHz).
Figure 12
Figure 12
Manufactured rectenna with the rectifier schematic.
Figure 13
Figure 13
RF-DC conversion efficiency for the rectennas at 868 MHz for various decade power densities.
Figure 14
Figure 14
Photograph of the experimental setup for the sensing node embedded and powered by using WPT system in the concrete structure.
Figure 15
Figure 15
Developed sensing node for BLE communication.
See this image and copyright information in PMC

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