Projects:2020s2-7111 3D printed recycled plastic antennas

Nowadays, the demand for reliable WiFi networks is very apparent and is in a constant growth. Thus, in order to provide high-quality and low-cost WiFi networks to consumers, the need for inexpensive and high performance antennas is critical to meet the high demand. In this project, 3D printed antennas which are made of recycable plastic will be investigated. Tests will be conducted to verify that these antenna meet the required performance criteria.

Introduction

This project aims to make use of recyclable plastic as a filament to 3D print antennas for WiFi networks. This will not just make use of the common household waste and reduce pollution, but also lead to a mass production of budget-friendly antennas through the usage of 3D printing technology. These high performance antennas will be designed through CST Studio Suite 2019 which will then be 3D printed and tested in the anechoic chamber and real outdoor WiFi setting to make sure that they meet the specifications set for WiFi networks.

Project team

Project students

• Sultan Ahmed Saleh Al-Hammadi

Supervisors

• Prof. Christophe Fumeaux
• Dr. Shengjian Jammy Chen
• Mr. David de Haaij (Black Art Technologies)

Objectives

• 3D printable antenna structure
• Made of recyclable plastic and least amount of metal
• Operates at 2.4-2.5 GHz and 5-5.8 GHz with gain higher than 10 dBi
• Maximum dimension of 30 cm
• Sidelobe levels need to be below -10 dB

Motivation

WiFi is considered to be one of the greatest inventions in the last 25 years due to its countless applications. To enable such a technology, antennas are need to transmit and receive electromagnetic waves. There are many WiFi antennas which already exist in the literature and on the market. However, as customer demands are increasing while noting that global warming is a massive problem, antennas with the following characteristics are required: • Highly directive and environmentally friendly. • Inexpensive and easy to manufacture. • High performance.

Launcher Design

The proposed device consists of two main components: the launcher, and the radiator. In this project, three distinct launchers were investigated. The first one is a rectangular waveguide which is widely used in the industry. The cut-off frequency can be controlled by changing the dimensions of its cross section [1]. However, since it is required to have a dual-band antenna, there would be higher modes of propagation at the higher frequency band (i.e. the 5.4 GHz band). This would lead to a problem known as modal dispersion which results in a spread of “the temporal duration of the pulse, which limits the bandwidth.” This is due to the fact that each mode “travels with a different group velocity”, causing propagation modes to be delayed with respect to each other [2]. The other issue is that it is a relatively expensive and complex structure to manufacture.

The second kind of launchers were flat metal plate antennas. They are basically single sheets of metal with slots to create the desired resonance frequencies. Although they sound easy to understand, they have some serious issues. Creating the slots precisely is an extremely difficult task and hence it would be difficult to match the results obtained from simulations. The other problem is as a result of soldering the coaxial cable directly to the metal plate. It causes a return current on the outer surface of the outside conductor leading to unpredictable effects on the reflection coefficient for instance.

Lastly but not least, printed circuit boards or planar antennas were examined. They essentially have two metal sheets on both sides of a substrate. One side has a ground plane which is used to reflect the waves travelling in the opposite direction of the desired direction. The one used in the proposed device is similar to the one discussed in [4] and is called a double-sided dipole antenna. The substrate chosen is FR4 because it is one of the cheapest and widely used in the industry. In principle, it is similar to a Yagi-Uda antenna but is on a PCB. The longer leg is used to excite electromagnetic waves with the higher wavelengths (i.e. 2.4-2.5 GHz). The middle and shorter leg are combined to obtain a wider impedance bandwidth between 5 GHz to 7 GHz. This planar antenna was fabricated by PCBway which is a reliable Chinese company based in the US.

Radiator Design

The radiator can be thought of as an auxiliary which is used to boost the gain of the antenna. The higher the gain, the more directive the antenna. Figure 4 shows the dielectric rod antenna which is the radiator of the proposed device [5]. It can be noted that the first section grows in size and this is to capture as much radiation as possible from the launcher while minimising the reflections along the -z-axis. However, if this section was not tapered, then the wavefronts at the different frequencies will spread too much to the point where directivity and gain are lost. Section 3 is a long and tapered section which focuses the radiation along the axis of the rod and hence bosting the gain. Section 4 introduces an additional tapering to minimise the reflections and allowing the electromagnetic waves to propagate smoothly to free space.

The rod is fabricated using the 3D printers available at the University of Adelaide with a recycled HIPS (High Impact Polystyrene) from a Canadian supplier called Nefilatek. Initially, three cubes with an infill percentage of 100% were printed to determine the relative permittivity of the material along with its loss tangent. As shown in Figure 5, its relative permittivity is close to 1 (i.e. free space) which explains why the device is relatively big and heavy compared with the commercial antennas.

Results

To test the reflection coefficients, a network analyser was used. As illustrated in Figure 6, the simulated and measured S11 parameters indicated that the launcher can be used for 2.2-2.8 GHz and 5-7 GHz. Once this radiator is coupled with the launcher, almost no variations where observed in terms of the frequency coverage (refer to Figure 7). Two holders were designed to hold the proposed device in the two orthogonal orientations. The whole device was then tested in the anechoic chamber at the University of Adelaide. This was to obtain the radiation patterns as demonstrated in Figures 8 and 9. From these figures along with Figure 10, it can be said that the proposed device overall resulted in a gain higher than 10 dBi. The small variations are mainly due to the fabrication errors from the 3D printers.

Conclusion

• Highly directive and environmentally friendly antenna (gain ≥ 10 dBi).
• Operates at 2.23-2.89 GHz and 5.11-7.01 GHz.
• Excellent match between measured and simulated results.
• Potential to improve sidelobe levels and weight of dielectric rod antenna.

References

[1] C. A. Balanis, Antenna Theory: Analysis and Design, 4th ed. New York, NY, USA: Wiley, 2016.

[2] C. Pollock and M. Lipson, Integrated photonics, 1st ed. Boston, MA, USA: Springer Link, 2003.

[3] S. W. Su and J. H. Chou, “Low-cost flat metal-plate dipole antenna for 2.4/5-GHz WLAN operation,” Microw. Opt. Technol. Lett., vol. 50, no. 6, pp. 1686–1687, Jun. 2008.

[4] Z. X. Yuan, Y. Z. Yin, Y. Ding, B. Li and J. J. Xie, “Multiband printed and double-sided dipole antenna for WLAN/WiMax applications,” Microw. and Optical Technol. Lett., vol. 54, no. 4, pp. 1019-1022, Apr. 2012.

[5] I. C. Göknar and L. Sevgi, Complex Computing-Networks: Brain-like and Wave-oriented Electrodynamic Algorithms, 1st ed. Berlin, HD: Springer Link, 2006.