How to mitigate frequency interference in radio astronomy

By Gregory Hellbourg, Scientist, Cahill Center for Astronomy and Astrophysics, California Institute of Technology (Caltech), US, and Kaushal Buch, Senior Engineer and Group Coordinator, GMRT Backend Systems, Giant Metrewave Radio Telescope, National Centre for Radio Astrophysics (NCRA-TIFR), India

Radio astronomy detects extremely weak electromagnetic signals, often far below receiver noise. These signals carry essential information about phenomena ranging from distant galaxies to transient cosmic events.

In practice, however, radio telescopes must operate in an increasingly complex radio-frequency spectrum landscape shaped by numerous active and interconnected communication systems.

Radio frequency interference (RFI) has become a central challenge for scientists dealing with outer space – and not least for radio astronomers. Signals from telecommunication systems, broadcasting, and satellites can be many orders of magnitude stronger than cosmic signals.

The key question is: How much astronomical information can still be recovered?

Radio telescopes are passive receivers reliant on a limited range of protected frequency allocations. While some bands are protected under the Radio Regulations, scientific observations often require broader access, creating a coexistence challenge with active services.

RFI affects radio astronomy depending on its strength and characteristics. Astronomical signals are extremely weak, many tens of decibels below typical communication signals. Weak interference may remain within the receiver’s linear response and simply add unwanted power.

Even then, contaminated channels are often excluded, reducing sensitivity. Stronger signals can generate harmonics and intermodulation products, contaminating frequencies beyond the original emission, within the emitter and receiver.

At higher power levels, interference can cause compression or saturation. In extreme cases, it can damage sensitive front-end components, leading to irreversible data loss.