Projects:2018s1-196 Concealed Wearable Antennas

The aim of this project is to design two button antennas as wearable technology that can be attached to the clothes. The button will be designed based on metallic antenna plates and another one based on dielectric plates. The simulation tools of Computer Simulation Technology, CST will be used for simulation and the designs will be fabricated and tested in real life. The antennas also should be designed with 2.4 GHz and 5.8 GHz frequency band and have Omni-directional radiation patterns.

Introduction

The wearable technology become important to our daily lives in this new development era. So, button antenna is chosen as the best candidate for wearable antenna. As we know, buttons are already included in many clothes that we wear every day. They can be located in different areas on textiles as well such as on t-shirt, jeans, jackets and others. Some of them also using multiple buttons on a cloth. So buttons are already heavily used in textiles or clothing. Users already accepted the look of the button so there is no need for users to refine the fashion or accept the new concepts as they already comfortable wearing buttons on their daily life. Many of them also already made from metal so incorporating metallic button in the antenna would not be a new concept to the users. The buttons also have small and circular in shape as well in which they are compact and easy to carry. Hence, there is an opportunity for buttons to serve a double-purpose which is ideal when looking at the wearable technology.

Project team

Project students

Christian Colombo
Siti Nurfatinah Faizal

Supervisors

Prof. Christophe Fumeaux
Dr. Shengjian Chen (Jammy)

Project status

Design, fabrication and testing completed.

Design Process

Design A: Siti Faizal

Design Overview

The first design is formed from a metallic, top-loaded monopole antenna, comprised of two metal discs separated by a low permittivity dielectric material. The antenna is fed by a microstrip line, which minimises the height of the assembly, and allows for it to be more easily incorporated into clothing. There is also a center pin in the middle of the antenna which connect the top plate with the ground plane in order to increase the strength of the button.The antenna then is mounted on a PF-4 Foam substrate with a conductive fabric ground plane.

Fig 1. Simulation Model of Design A

File:Dimension.png

Fig 2. Parameter List of Design A

Simulation Results

Figure 3 shows the performance of the antenna in terms of return loss (dB) vs the frequency (GHz). It has a desirable return loss of -30.65 dB at the low frequency of 2.45 GHz and -12.114 dB at high frequency of 5.8 GHz. As the reflection coefficient is lower at low frequency compared to high frequency band, so it is optimized for lower frequency operation. The major factor of getting the accurate matching frequency at both bands is by varying the diameter of the discs, cylinder and height of the antenna.

Fig 4. S-parameter result

The radiation patterns of the antenna are shown in Figure 4 and 5. At low frequency band (2.4 GHz), the antenna has an Omni-directional pattern with gain 3.44 dBi. It has a doughnut shape pattern where the antenna is highly radiated around the antenna. Meanwhile for high frequency band (5.8 GHz), it has a directive pattern in which the antenna is highly directional and a lot of powers is been pointed towards upper direction. It has 3.88 dBi gain which is higher than the low frequency gain. The radiation patterns for both frequency seem to have a good pattern and being directed correctly as predicted.

Fig 4. Radiation pattern at 2.45 GHz

Fig 5. Radiation pattern at 5.8 GHz

Fabrication

To do the fabrication, the dimensions of design antenna need to match with the materials that are planned to use. As for the top disc, RT/duroid 5880 is chosen. It is a laminate that consist of two copper plates at upper and bottom part and is filled with a dielectric with low permittivity of 2.2. It is a glass microfibre reinforced PTFE composites and is easily to cut which is suitable for the wearable button antenna.The cylinder part is made of a coaxial cable (RG401/U). The cable has three layers of material. The inner conductor which is the centre pin is made of copper rod, the dielectric type is a Teflon and the shield material is a copper tube. This cable can handle the frequency of 10 GHz and with impedance of 50 Ohms. The antenna is the mounted on a substrate with conductive fabric as a ground plane. A PF-4 Foam is used as the substrate as it is flexible to be put on clothes.

Fig 6. Fabricated Metallic Button

Testing

The testing process was done in an anechoic chamber in which the room is made of absorbing materials where it eliminates reflection and external noise caused by the electromagnetic waves. The antenna was tested for its performance of the return loss and radiation pattern. The return loss was measured by the Network Analyzer where it displayed the S-parameter result. The radiation pattern of the antenna was tested in the chamber. The antenna was placed on the positioning systems where it is rotating 360 degrees so the radiation pattern can be measured at all angles. Then, the transmitting antenna will transmit the signal to the receiving antenna and the data was sent to the PC to be recorded. Furthermore, the Standard Gain Horn Antenna also was measured. It is use for gain reference for antenna measurements. The measured gain at 2.4 GHz and 5.8 GHz was compared with the reference gain and find the difference between them.

Fig 7. Anechoic chamber

Fig 8. Network Analyzer

Fig 9. PC

Fig 10. Standard Gain Horn Antenna

Testing Results