What is anti-jamming in satellite communications?
Anti-jamming (AJ) refers to the technical features incorporated into satellite communication systems that allow them to maintain operation in the presence of intentional RF interference (jamming). As satellite communications have become critical military and national security infrastructure, anti-jamming capability has become a core requirement for government and defence SATCOM programmes — and increasingly a commercial consideration after the Viasat KA-SAT attack in 2022.
Anti-jamming techniques
Spread-spectrum waveforms: Direct sequence spread spectrum (DSSS) distributes signal energy across a wide bandwidth, making the signal appear as noise to a narrowband jammer. To jam a DSSS signal effectively, the jammer must cover the entire spread bandwidth — requiring proportionally more power. Military satellite waveforms (MILSTAR, Advanced EHF) use extreme frequency spreading. Frequency hopping: Rapidly switches carrier frequency in a pseudo-random pattern known only to legitimate transceivers; a jammer must cover all possible frequencies simultaneously to block the link. Null steering / Adaptive antenna processing: Phased array receivers can place an antenna pattern null in the direction of the jammer while maintaining sensitivity toward the satellite — rejecting the jamming signal by 30–50 dB. Higher frequency operation: EHF (millimetre wave) terminals with narrow, highly directional beams are inherently more difficult to jam than lower-frequency, wider-beam L-band systems.
Ground terminal considerations
Anti-jamming features add cost and complexity to terminals. MILSATCOM terminals (used by NATO forces) incorporate AJ waveforms as a baseline. Commercial VSAT terminals used in conflict areas (including Starlink in Ukraine) rely on the satellite operator's monitoring systems to detect and localise uplink jammers, and on the terminal's narrow-beam phased array for some geometric rejection of ground-based jammers. SpaceX has reportedly updated Starlink firmware to improve resilience against jamming attempts observed in Ukraine operations.