What is cross-band interference and how is it mitigated in satellite systems?

• A. Interference from weather; mitigated by larger antennas.
• B. Interference from adjacent bands; mitigated by filtering, shielding, receiver filtering, and careful frequency planning.
• C. Interference from ground noise; mitigated by boosting transmitter power.
• D. Interference from solar flares; mitigated by scheduling.

Answer: (B)

Cross-band interference happens when energy from one frequency band leaks into a neighboring band, causing signals in that adjacent band to degrade. In satellite systems, channels are packed close together, and real-world equipment isn’t perfectly selective. Energy from a strong channel can spill over due to imperfect filtering, out-of-band emissions, intermodulation products, LO leakage, or coupling between components. The result is added noise or distortion in the nearby channel, which can raise the error rate and reduce link performance.

Mitigation focuses on keeping unwanted energy out of the target band. This is done by enforcing strict transmitter emission masks so the transmitted signal stays within its own band, and by placing robust filters at the receiver front-end to reject any out-of-band energy that arrives. Shielding helps prevent RF leakage from cables, connectors, and enclosures, while high-isolation components like duplexers and careful RF layout further reduce leakage paths. Thoughtful frequency planning, including appropriate channel spacing and guard bands, minimizes the chance that adjacent-band energy will interfere with a neighboring channel. Keeping the system within linear operating ranges also reduces intermodulation that could spill into nearby bands.

Weather-related interference, ground noise, or solar activity involve different phenomena and mitigation methods, so they aren’t addressing cross-band leakage in the same way.