Simulation and Measurement of Locomotive Antennas in the Installed State Based on a Scaled Mockup

Accurate characterization of locomotive antennas is key to safe and robust railway signaling and control communication. With the introduction of new technologies and the foreseeable migration from the GSM-R standard towards FRM CS, new wireless applications and specifications arise, and suitable antenna solutions need to be developed and tested. Moreover, the rooftops of modern locomotives present a dense and harsh environment; therefore, potential antenna mounting spaces should be carefully evaluated to avoid undesirable degradations of the antenna radiation patterns. Due to the electrically large and complex structure of locomotives, full-scale testing is challenging to perform, especially under laboratory conditions. Antenna measurements with geometrically scaled models present a powerful alternative to address this issue. In this paper, we present and discuss antenna measurement results of a scaled locomotive mockup. The mockup incorporates two different cabin geometries, one with a step-like rooftop contour, and one with a smooth slightly tilted geometry. First, the optimum scaling factor was identified and validated through numerical simulations. Afterwards, antenna measurements with a scaled locomotive mockup were carried out in our automotive antenna measurement facility VISTA. The measured results were compared with the numerical simulations, where a good correlation above 80 % was found. Secondly, the impact of the rooftop geometries, and superstructures on the roof has been investigated for a range of operational frequencies between 700 and 2600 MHz. The results reveal that the parasitic impact of the antenna environment becomes more pronounced at higher frequencies.

I. Introduction

The global demands for transport are growing rapidly. Given present trends, passenger and freight activities will more than double by 2050 [1]. Among all modes of transport, railway transportation is the most energy-efficient for freight and passengers, and the key element of the Green Deal of the European Commission [2]. The rail industry requirement and desire to achieve an on-board connected environment for both operational purposes and customer applications have resulted in the need to install a wide variety of wireless functionalities and transceiving antennas on the rooftop of locomotives [3]–[5]. Accurate characterization of these locomotive antennas is key to safe and robust railway signaling and control communication. Moreover, with the introduction of new technologies and a foreseeable migration from GSM- standard towards Future Railways Communications Systems (FRMCS), new wireless applications and specifications arise, and suitable antenna solutions need to be developed and tested. It is known from previous studies in the automotive sector that the electromagnetic interaction between the car chassis and the antenna alters its radiation performance compared to a free-space operation [6]–[8]. Similar interaction is also to be expected for locomotive antennas due to the conducting chassis. Moreover, the rooftops of locomotives present a dense and harsh environment; therefore, potential antenna mounting spaces should be carefully evaluated to avoid undesirable degradations of the antenna radiation patterns. Considering the significant influence of the locomotive body on the radiated performance of the installed antenna, the characterization of these locomotive antennas must be performed together with the locomotive before they are put into service. Fig. 1.

Measurement setup in the virtual road simulation and test area (vista) depicting locomotive antenna measurements under free-space conditions through a multi-probe measurement arch [9]. The scaled locomotive mockup is lifted to the chamber center using a pneumatic lift. Antenna measurements are possible from zenith till 20° below horizon. The range from 111 ° … 180° in co-elevation is truncated.