Train antennas are the physical interface between rolling stock and the radio networks that carry safety-critical communications, train control, operational telemetry, and passenger connectivity.
A modern train carries antennas for multiple independent radio systems spanning a broad frequency range. The rooftop is where the railway’s connectivity and communications layer becomes physical hardware.
Functions and frequency allocations
GSM-R uses the 876–880 MHz and 921–925 MHz bands; FRMCS adds the 1900–1910 MHz Time Division Duplex (TDD) band. Passenger Wi-Fi aggregates Long-Term Evolution (LTE) and 5G signals from commercial mobile networks across 700 MHz, 800 MHz, 1800 MHz, 2100 MHz, 2600 MHz, and higher bands.
GPS/Global Navigation Satellite System (GNSS) receivers for positioning and odometry supplementation use the L1 band at 1575.42 MHz. ETCS position calibration instead relies on Eurobalise transponders mounted in the track, read by a dedicated antenna under the vehicle rather than by rooftop equipment.
Each system has its own antenna geometry, polarisation, and mounting requirements. On a modern high-speed train the result is a rooftop populated with multiple radomes at defined positions along the car body.
Their placement is managed to avoid mutual interference while preserving each system’s coverage geometry.
Multiband integration for the FRMCS transition
During the transition from GSM-R to FRMCS, rolling stock must support the 900 MHz and 1900 MHz bands simultaneously. Dual-band antennas combining both ranges in a single housing allow operators to retrofit existing rooftop positions rather than add mounting points — a resource constrained by wind load, roof space, and interference budgets.
FRMCS onboard antenna systems are designed for MIMO (Multiple Input Multiple Output) operation, delivering 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 configurations covering both the 900 MHz and 1900 MHz bands.
The OBRAD (On-Board Radio Interface) concept, described in European Telecommunications Standards Institute (ETSI) technical report TR 104 006 V1.1.1 (January 2025), defines how onboard antenna and radio modules connect to the train gateway; formal standardisation for vendor-independent interoperability is proceeding through ETSI TS 104 127.
Standards and certification
Antennas installed on rolling stock must comply with EN 50155 for environmental requirements — vibration, temperature, humidity, electromagnetic interference (EMI) — and with EN 50121-3-2 for electromagnetic compatibility of equipment on rail vehicles. For the radio frequencies themselves, the ETSI standards governing each band apply.
Trackside antennas for GSM-R and FRMCS are designed with narrow half-power beamwidths to concentrate signal along the track alignment and limit interference into adjacent spectrum and residential areas — one manufacturer’s portfolio lists 33° as a typical figure, alongside wider-beam variants for other coverage needs.
According to the company’s own product materials, Huber+Suhner has introduced dual-band GSM-R/FRMCS trackside antennas operating simultaneously at 900 MHz and 1900 MHz, positioned to let infrastructure managers install FRMCS-capable hardware during current GSM-R maintenance cycles.