Every satellite is, at heart, a radio in space. Whether it's relaying TV channels from GEO, delivering broadband from LEO, or downloading scientific data from a Mars probe, the basic problem is the same: get a useful signal across hundreds or millions of kilometres of vacuum without losing it in noise.
Frequency Bands
Satellite operators use specific slices of the radio spectrum, each with trade-offs:
- L-band (1–2 GHz) — GPS, Inmarsat, mobile satellite — penetrates rain and foliage.
- S-band (2–4 GHz) — telemetry, weather radar, NASA's Tracking and Data Relay Satellite System (TDRSS).
- C-band (4–8 GHz) — legacy TV broadcast, very rain-tolerant.
- Ku-band (12–18 GHz) — modern TV, VSAT, Starlink user links.
- Ka-band (26–40 GHz) — high-throughput broadband, gateway links.
- Optical (laser) — emerging inter-satellite and ground links with massive bandwidth.
Antennas and Footprints
A satellite's antenna determines its footprint — the area on Earth that can see it with adequate signal strength. Wide-beam antennas cover whole continents at low data rates; narrow spot beams concentrate power on small regions for high throughput. Modern high-throughput satellites (HTS) use hundreds of spot beams and reuse frequencies across them, multiplying capacity.
Link Budgets
Engineers calculate a "link budget" that tracks every dB of signal: transmit power, antenna gain, free-space path loss, atmospheric absorption, rain fade, and receiver noise. The difference between expected signal-to-noise and required signal-to-noise is the link margin. Too little margin and the link drops in bad weather; too much and you've wasted satellite capacity.
Modulation and Coding
DVB-S2X, the standard for modern satellite comms, can adapt modulation (QPSK, 8PSK, 16APSK, 32APSK, up to 256APSK) and forward-error-correction in real time based on link conditions. That's why your satellite TV keeps working in light rain — it falls back to a more robust modulation automatically.
From LEO to GEO
- GEO comms — one satellite covers ~⅓ of Earth, but ~250 ms one-way latency.
- MEO comms — fewer satellites than LEO, lower latency than GEO (e.g. SES O3b).
- LEO comms — large constellations, ~25 ms latency, complex handovers.
Watch satellites pass overhead on the live tracker, or see how the Starlink constellation orchestrates handovers in our Starlink guide.