Antennas on mobile platforms: stabilisation, pointing and design trade-offs
Maintaining the satellite link on mobile platforms constitutes one of the most demanding engineering problems in embarked SATCOM systems. Unlike fixed installations, an antenna mounted on a ground vehicle, an aircraft or a vessel must continuously compensate for pitch, roll and yaw movements, maintaining pointing towards the satellite with angular errors below fractions of a degree in the majority of operational scenarios. This requirement necessitates the integration of inertial stabilisation systems operating in a closed loop with the pointing mechanism, increasing the mechanical complexity, energy consumption and total mass of the assembly. Solutions based on motorised parabolic antennas offer high gain with relatively compact apertures, but present inherent limitations in high-dynamics environments. Mechanical actuators have a limited frequency response, which introduces latency in the correction of abrupt movements. Furthermore, moving parts exposed to vibration, temperature and humidity represent degradation vectors for reliability throughout the system life cycle. On platforms where the mission profile involves high accelerations or adverse environments, these factors directly condition link availability. Electronic phased-array antennas eliminate the moving parts of the pointing mechanism by electronically controlling the phase of each radiating element. This allows beam scanning speeds several orders of magnitude higher than mechanical solutions, with repointing times on the order of microseconds. However, this architecture introduces significant trade-offs: radiation efficiency decreases with the scan angle relative to broadside, the thermal dissipation of the active transmit and receive modules requires specific thermal management solutions, and the cost per unit of aperture remains higher than that of equivalent mechanical solutions in terms of absolute gain. The balance between size, weight and power, commonly referred to as SWaP in the embarked systems literature, is the integrating parameter that determines the viability of a solution for each class of platform. In tactical ground vehicles or fixed-wing aircraft, mass and power budgets are strict, which favours low-profile phased-array architectures with moderate gain. On naval platforms or larger aircraft, it is possible to consider hybrid solutions combining coarse mechanical stabilisation with fine electronic pointing. The regulatory framework for spectrum access, together with the electromagnetic compatibility requirements imposed by bodies such as the ITU or ETSI, adds an additional layer of constraints that conditions the design from the early stages of the project.
NASSAT - Network Satellite Systems