In the RFID sensor networks (RSN), the orientations of the antennas used in the network nodes have a significant influence on the propagation characteristics. In this article, we investigated the effects of the two antennas' orientation of different radiation and polarization on the multipath propagation characteristics. This study is evaluated in a typical indoor environment by computer simulations based on the three-dimensional (3D) ray-tracing method. This method is based on geometric optics and uniform diffraction theory and also it offers significant advantages in terms of accurate and comprehensive prediction of propagation characterization. The simulations have been performed at frequency 915 MHz and the propagation characteristics are compared in terms of received power level ( ) and Root-Mean-Square (RMS) delay spread for a quasi-isotropic 3D cubic antenna with circular polarization and for an omnidirectional dipole with linear polarization in the LOS, NLOS, and OLOS scenarios.

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Several antenna designs have been made in order to obtain a novel electrically small 3D UHF spherical antenna (ka = 0.1916), which has a resonance frequency close to 915 MHz, produces a quasi-isotropic radiation with an opening angle equal to 360° in the whole space, and is used for RFID, WSN, and RSN applications. These antennas are based on different shapes and are wrapped on the Styrofoam sphere surface of dielectric constant close to air (ɛr=1.06). A T-match configuration is used to adapt the input impedance of antennas to a value of 50 Ω. The antennas form allows for placing the sensor electronics in its interior, to reconfigure it for numerous values of impedances and to operate it in other ISM bands by adjusting their geometric parameters.

In the RFID sensor network (RSN), the devices communicate with each other by RF waves using the antennas through a propagation channel. A poor communication between these devices results in either a significant economic loss or security threats. The communication problems can have several origins depending on the type of antenna used and the nature of the propagation channel. In this work, our objective is to limit the communication problems between the nodes of this network that are linked to the characteristics of an indoor propagation channel. The goal is to predict the channel characteristics using the 3D ray tracing method in order to select the appropriate transmission parameters such as transmission power and duration of a symbol. To achieve this, we have modeled a building that is sectioned as a propagation channel where network devices are deployed for control and monitoring. The communication was made at 915 MHz using the quasi-isotropic 3D cubic antenna that we designed as well as a conventional dipole antenna in order to compare the results. We have found that the use of the 3D cubic antenna gives several advantages to the RFID sensor network compared to the most commonly used conventional dipole antenna, such as a transmission power of 0 dBm which automatically leads to an increase in the lifetime of the devices, as well as a minimum symbol duration of around 219.78 ns which gives a high bit rate.