Antenna Evaluation for Vehicular Applications in Multipath Environment

Licentiatavhandling, 2017

Antennas are essential components in any wireless communication system. To evaluate them is challenging, especially when new technologies are emerging. Future intelligent transport systems, where vehicular communications play an important role will cover important aspects such as traffic safety and traffic efficiency. These applications will be covered by technologies such as IEEE 802.11p and LTE. For these emerging technologies, traditional methods for measuring the vehicular antennas such as anechoic chamber measurements or expensive and time-consuming field measurements may not be enough or suitable. Thus a new method for evaluating the antennas performance is desirable. A method that includes the multipath environment to give an idea of the antenna performance in the whole system and at the same time be able to be applied at early stages of product development. This thesis aims to provide such method. The thesis is divided in two parts. The first part contains an overview and background of important concepts needed for development of methods for evaluation of vehicular antennas. In the second part, the papers that constitute the core of this work are appended. In Paper A, we evaluate the vehicle’s antenna performance using only simulations. We start by defining the multipath environment for vehicle-to-vehicle and vehicle-to-infrastructure (V2X) communication. Then, the V2X environment is simulated using a multipath simulation tool to evaluate the vehicle’s antennas radiation patterns placed at different positions on the vehicle. This will result in the received power cumulative distribution functions (CDFs) for the voltage samples at the receiving antennas port. In Paper B, we present the design and evaluation of an antenna module for IEEE 802.11p and LTE technologies. The module is designed taking into consideration the available space and suitable placement on the vehicle. The proposed module is in accordance with the requirements for LTE and IEEE 802.11p technologies. This is validated with the analysis of the antenna efficiencies, S-parameters, radiation patterns, and diversity performance for the simulated and measured antenna module. Finally, Paper C presents a method for the evaluation of V2V antennas in a simulated measurement-based multipath environment. Here, a measurement campaign is performed to obtain the parameters (i.e., the angular received power spectrum) that define a realistic V2V multipath environment. These parameters are then introduced in a multipath simulation tool where the antennas radiation patterns are evaluated. Results are expressed in terms of received power CDFs. This method is validated by comparing the simulated and measured received power for two roof-top vehicle antennas.