Train antennas & multiband systems
Train antennas are the physical interface between rolling stock and the radio networks required for safety-critical communications, train control, operational telemetry, and passenger connectivity.
A modern train carries antennas serving multiple independent radio systems operating across a broad frequency range. GSM-R uses the 876–880 MHz and 921–925 MHz bands. FRMCS adds the 1900–1910 MHz TDD band.
Passenger Wi-Fi aggregates LTE and 5G signals from commercial mobile networks across 700 MHz, 800 MHz, 1,800 MHz, 2,100 MHz, 2,600 MHz, and higher bands. GPS/GNSS receivers for positioning and odometry supplementation use the L1 band (1575.42 MHz). Eurobalise loop readers for ETCS are typically inductive at low frequency and are not mounted on the roof.
Each of these systems has different antenna geometry, polarisation, and mounting requirements. The result on a modern high-speed train is a populated rooftop with multiple antenna radomes at defined positions along the car body, managed to avoid mutual interference while maintaining the coverage geometry each system requires.
Multiband integration for FRMCS transition
During the transition from GSM-R to FRMCS, rolling stock must support both the 900 MHz GSM-R band and the 1900 MHz FRMCS band simultaneously.
Dual-band antenna systems combining both frequency ranges in a single housing allow operators to retrofit existing rooftop positions rather than add new mounting points — which is constrained by wind load, roof space, and interference budgets.
FRMCS onboard antenna systems are designed for MIMO (Multiple Input Multiple Output) operation to achieve the diversity gain and throughput required at train speeds up to 350 km/h and beyond.
The 5GRAIL research project, which produced the first FRMCS prototype validated in real field conditions, specified MIMO antenna configurations covering both the 900 MHz and 1900 MHz bands. The OBRAD interface standard (ETSI TR 104 006 V1.1.1, January 2025) governs how onboard antenna and radio modules connect to the train gateway, providing vendor-independent interoperability.
Standards and certification
Antennas installed on rolling stock must comply with EN 50155 for environmental requirements — vibration, temperature, humidity, EMI — and EN 50121-3-2 for electromagnetic compatibility of equipment installed on rail vehicles.
For the radio frequencies themselves, compliance with ETSI standards governing each band applies. Trackside antennas for GSM-R and FRMCS are designed to provide lineside coverage with narrow half-power beamwidths — typically 33° — to concentrate signal along the track alignment and limit interference into adjacent spectrum and residential areas.
The antenna manufacturer Huber+Suhner has introduced dual-band GSM-R/FRMCS trackside antennas operating simultaneously at 900 MHz and 1900 MHz, designed to allow infrastructure managers to install FRMCS-capable hardware during current GSM-R network maintenance cycles, avoiding a later full replacement.