On-body Transmission Single-band Diamond Dipole Antenna with Waveguide Jacke

Received Dec 12, 2017 Revised Feb 27, 2018 Accepted Mar 23, 2018 This paper presents the investigation of on-body transmission single-band diamond dipole antenna with three different jackets. The jackets are named as normal jacket, grounding jacket and waveguide jacket. The on-body transmission is measured using two flexible single-band antennas attach to the jackets. A man with the height of 180 cm and 75 kg weight becomes as a model for the real measurement. The measurement is conducted in small space area by using portable network analyzer with flexible network cable. The measurement results show that the best performance for on-body transmission is with waveguide jacket. 10 dB transmission improvement is archived when the antenna is placed above the waveguide jacket compared to the normal jacket. It is found that the transmission of the antenna is also depends on the antenna orientation and further transmission lossess occur when the antennas are placed above the grounding jacket.


INTRODUCTION
Nowadays, human body has become a part of wearable wireless networking devices as the electronic devices become smaller and cheaper. Since human body becomes a part of communication network, the integration of wireless sensor network (WSN) and wireless personal area network (WPN) become body-centric wireless communication.
Due to complexity of the human body, many researchers around the world interested to investigate in this body-centric wireless communication area. Firstly, some fabric antennas have been investigated by [1]- [3] since 1999. They are using felt fabric as substrate and Zelt fabric as conducting element. However, the performance of the antenna deteroriated when the antenna is put above the human body [4]. The bulky size of coaxial port that has been used in [5][6] also is not suitable for wearable application.
Theoritycally, the main characteristic of an artificial magnetic conductor (AMC) to influence the propagation electromacnetic waves is in-phase reflection coeficient [7]. Previous researchers have presented that the AMC may reduce the backward radiation and improve the gain of the antenna [8]- [9]. Then, sheetlike waveguide sheet is proposed by [10]- [13], 16] to reduce the distortion from the human body. The waveguide sheet is consisted of array of AMC. The function of the sheet-like waveguide is to reduce the transmission losses between the antennas.
In this paper, two single-band textile diamond dipole antenna which are operating at 2.4 GHz and 5.8 GHz are used to investigate the S21 transmission above three different jackets; normal jacket, grounding

MEASUREMENT SETUP
Two single-band diamond dipole antennas which are operated at 2.4 GHz and 5.8 GHz respectively have been used to be incorporated with three different jackets as shown in Figure 1. The jackets are made of fleece fabric named as normal jacket, grounding jacket and waveguide jacket. Normal jacket is a plain jacket while grounding jacket has attached with full ground plane fabric. The waveguide jacket is an array of AMC design from my previous work [4]. The orientation of the antenna is investigated above the jackets. The antennas are placed vertically and horizontaly above each jacket as shown in Figure 2. One of the antennas is placed in the middle of the jacket which acts as a transmitter (Tx) while the other antenna (Rx) position is varied at eight different locations. The locations are labelled alphabetically from A to H as shown in Figure 3. The distance between the antenns is fixed at 14 cm. The experiment is conducted in small space area. A man becomes a model to wear the jackets. During the experiment, he stands up and the transmission between the antennas is measured as shown in Figure 4. The gap between both antennas and the jacket is set to 3 mm by using a foam (σ r =1). Portable network analyser is used to measure the transmission performance of the antennas.

RESULTS AND DISCUSSIONS
The results are divided and analyzed into two sub chapter. The first sub chapter explains about 2.4 GHz antenna transmission while the 2nd sub chapter elobrates about 5.8 GHz antenna transmission.

S21 Transmission of 2.4 GHz Textile Diamond Dipole Antenna
The S21 on-body transmissions of the antenna with three jackets were investigated. Graph in Figure  4 presents the S21 transmission of 2.4 GHz antenna with normal jacket in horizontal orientation. Figure 5(a) and Figure 5(b) denote the vertical arrangement respectively. Graphs in Figure 6 depict the measured S21 of antennas with grounding jacket while Graph in Figure 7 represents the measured S21 of antennas with waveguide jacket. Figures 6(a) and 7(a) represent for horizontal antenna orientation and figures 6(b) and 7(b) represent vertical antenna orientation.
When the antenna is placed horizontally, good transmission of the antenna observed at position A and E. For horizontal orientation, the S21 peaks are -32 dB and -33 dB for position A and E. Position C and G represent parallel arrangement in vertical orientation with S21 peaks at -30 dB and -32 dB at resonance. Graphs in Figure 5 show no transmission occurs between the antennas. The S21 peaks at -60 dB for both horizontal and vertical orientation which is at noise level. Finally positions A and E represent parallel arrangement in horizontal orientation with S21 peaks at -24 dB and -20 dB above the waveguide jacket while positions C and G in vertical orientation with S21 peaks at -24 dB and -24 dB.
Graphs in Figure 8 show the comparison of measured S21 results from Figure 5 to 7. The best performance of S21 transmission from graphs in Figure 5 to Figure 7 is compared. It shows that the S21 peaks are improved by 8 dB and 13 dB at resonance for horizontal orientation. For vertical horizontal, 6 dB and 8 dB improvement is achieved when the antenna is placed above the waveguide jacket. When the antennas are placed above the normal jacket, the transmission is disturbed by the presence of human body. The waveguide jacket acts as a path for the wave to propagate between the antennas and improve the transmission.

S21 Transmission of 5.8 GHz Textile Diamond Dipole Antenna
The measured S 21 transmissions are plotted in Figure 9 to Figure 11 for antenna above normal jacket, grounding jacket and waveguide jacket. Figure 9(a), 10(a) and 11(a) show the 5.8 GHz diamond dipole 's transmission results in horizontal orientation while Figure 9(b), 10(b) and 11(b) depict the vertical horizontal.
Among the 8 positions varied, the best transmission is obtained when the antenna placed in parallel arrangement. For horizontal orientation, positions A and E represent the parallel arrangement and position C and G for vertical orientation. When the antennas are placed above the grounding jacket, the transmission occurs at the noise floor level. Transmission improvements at resonance 5.8 GHz are observed at both horizontal and vertical orientations. From the horizontal orientation results, the S 21 peaks are -28 dB and -30 dB with improvement of 10 dB and 8 dB from the transmission above the normal jacket. The comparison S 21 results in vertical orientation are shown in Figure 12(b). The S 21 peaks are -37 dB and -34 dB for position C and G above the normal jacket while -28 dB for both position C and G above the waveguide jacket.
From the presented results, the presence of waveguide jacket improves the antennas' transmission compared to normal jacket. The structures of the waveguide jacket itself which is articifial magnetic conductor (AMC) help the wave to propogate through it.

CONCLUSION
In conclusion, two single-band textile diamond dipole antenna with normal jacket, grounding jacket and waveguide jacket have been measured and investigated. The position of the antenna determined the transmission of the antenna. 10 dB improvement when both antennas in the same. The waveguide jacket provides clear transmission path and reduces transmission loss. The in-phase reflection characteristic in waveguide jacket is predicted to enhance the transmission between the antennas. Meanwhile, the ground jacket is not suitable for antenna propagation as presented in the results.
[16] Adel Y. I. Ashap 1  He is the project leader for all these grants. The total amount of these research grants are more than RM 2.5 million. One of his research product has been commercialized through UTM Spin off company. This is supported by UTM Symbiosis programme which is the collaboration between UTM and MTDC. The total amount of grant obtained from this programme is nearly RM 2 Million. Through research, which he has conducted throughout the years, he has been honoured with recognition nationally as well as internationally for the products invention. The total awards that he has received through national competition is 5 gold,