Path Loss Characterization of Horn-to-Horn and Textile-to-Textile On-Body mmWave Channels at 60 GHz Mouad Ghandi 1 , Emmeric Tanghe 2 , Wout Joseph 2 , Mustapha Benjillali 3 and Zouhair Guennoun 1 1 Laboratory of Electronics and Communications, EMI, Mohammed V University, Rabat, Morocco 2 iMinds - Department of Information Technology, Ghent University, Ghent, Belgium 3 Communications Systems Department, INPT, Rabat, Morocco Emails: mouad.ghandi.92@gmail.com, {emmeric.tanghe, wout.joseph}intec.ugent.be benjillali@ieee.org, zouhair@emi.ac.ma Abstract—Wireless body area networks have raised consider- able attention within the wireless personal area community. To optimize the network architecture and the energy consumption of on-body equipments, a good knowledge and understanding of the radio link and the propagation channel are required. This work addresses the influence of medium presence on the reflection loss of horn and textile antennas. In particular, the path loss in free space and under skin-equivalent phantom of horn-to-horn and textile-to-textile communications is presented. The obtained results show that the path loss differs considerably in the analyzed situations; with horn-to-horn links showing a path loss exponent between 1.13 and 2.35, while it is reaching 4.7 for textile-to- textile links. The obtained results provide additional input for the design of communications links in the context of future 5G and IoT eco-systems. I. I NTRODUCTION Body area networks (BAN) consist of a number of nodes and units placed on the human body or in close proximity such as daily wearable and accessories. BANs rely, theoretically, on Norton’s investigation of radio communication using small antennas [1]. An increasing number of research works deals with the development of mmWave BANs, identified as a highly attractive solution for future wireless BAN (WBANs), with a strong potential in health care environments, entertainment, identification systems, sports, smart homes, space and military applications [2]–[4]. In the last decade, the 60 GHz technology has attracted a huge amount of interest due to its various advantages compared to lower frequencies [5], [6]. In this unlicensed frequency range, a 7 to 9GHz bandwidth is typically available depending on the country. The advantages of the 60GHz band include high-speed links for wireless personal area networks (WPANs) and wireless local area networks (WLANs) and future WBANs, more compact systems compared to lower frequencies, and higher levels of security. Propagation in the 60 GHz band is characterized by a high atmospheric attenuation due to the free space loss and resonant oxygen- induced absorption. On the other hand, the interaction between the human body and the millimeter waves is characterized by a relatively high reflection, due to the contrast between the dielectric permittivity of the skin and the free space. Furthermore, since the penetration depth at 60 GHz is around 0.5 mm, the penetration is mainly limited to the superficial layers of the human skin [7]. In this work, two types of mmWave antennas (namely, horn and textile antennas [8]) are considered. In particular, we investigate the influence of the skin-equivalent phantom on the antenna parameters for different antenna–phantom distances. In addition, the path loss (PL) in free space and along homo- geneous and layered mediums of the horn-to-horn and textile- to-textile communications is analyzed and characterized. Both measurements and simulation results are presented to illustrate the analysis. The paper is organized as follows. Section II presents the characteristics of the considered antennas, and the influence of the medium on the antenna parameters is discussed in Sec- tion III. In Section IV, the path loss characterization of horn- to-horn and textile-to-textile communications is presented in details, based on simulations and measurements, and conclu- sions are drawn in Section V. II. ANTENNAS DESIGN A. Horn Antenna Design The Horn antenna used in measurements and simulations consists of a 22 × 16 mm external aperture and a length of 74 mm (cf. Fig. 1 (a) and (b)). Its gain in free space is 19.5dBi, and the -10dB bandwidth is 10GHz centered around 60 GHz. Fig. 2 highlights the comparison between measured and simulated reflection losses in free space. To model the source, we used the wave-guide source proposed by SEMCADx. We note that this source does not take into consideration the connector effect, which explains the difference that some perturbations/fluctuations can be observed in measurements while they are absent in simulation. In addition, in real laboratory conditions where the free space is not perfect, a slight difference with simulation is normally expected, and it is expected to increase when operating at high frequencies with small antennas.