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Integrated (Smart) GNSS Antennas and Their Railway Applications
This article first appeared in the Railway-News magazine Issue 3 2023.
In a previous Railway-News article, ‘Precise Positioning for Railway Vehicles’, some of the fundamentals of Global Navigation Satellite System (GNSS) operation were described, including pseudo-random noise (PRN) code-based and carrier phase-based measurement methods for position calculations.
Also discussed was the use of real-time kinematic (RTK) corrections via base/rover GNSS receiver pairing to achieve sub-6cm accuracy. RTK accuracy is required to improve rail safety and productivity, especially in autonomous systems.
Briefly recapping, GNSS antennas require a stable phase centre, predictable phase centre variation, a design that mitigates multi-path and supports deep out-of-band filtering of interfering RF signals (e.g. 5G cellular signals). At the same time, the antenna must be capable of receiving GNSS and augmentation (correction) signals broadcast from medium earth orbits and geostationary satellites, respectively.
Benefits of a Smart GNSS Antenna
Traditional GNSS installations placed the GNSS antenna on the roof or a mast and ran a coaxial RF cable to the receiver. This design is suitable for installation where the antenna and antenna cable are not subject to RF noise. Today’s installations are increasingly complicated, and often, sensors are collocated; therefore, both the antenna and RF cables are subject to interference from these sensors or vehicle communications (RF signals).
In a Smart Antenna, the GNSS antenna and receiver are in the same enclosure, often on the same PCB, and are shielded from these other sensors and RF noise. A smart antenna design provides the cleanest and purest signal to the receiver. With a clean and pure signal, the receiver can estimate the most accurate and precise measurements.
Tallysman’s TW5390 Smart Antenna Features
Tallysman’s TW5390 smart GNSS antenna integrates the TW3972, American Association of Railways (AAR) certified GNSS antenna and the u-blox F9x family of GNSS receivers. The antenna has many key features such as multi-constellation, multi-band correction support (including L-band options), a low axial ratio that provides excellent multi-path mitigation, a precisely calibrated phase centre, Tallysman’s eXtended Filtering (XF), a low-noise amplifier that ensures a low noise figure and strong signal to noise ratio (C/No).
