Satellite Communication Link Budget

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This Satcom Link Budget implements an engineering-grade bent-pipe satellite communications link budget intended for trade studies, design verification, and sensitivity analysis. It models both uplink and downlink paths using standard RF link-budget methodology, incorporating free-space loss, antenna gains, system noise temperature, and a structured set of atmospheric impairments including gaseous absorption, rain attenuation, cloud loss, scintillation, and polarization effects. The model supports a range of frequency bands and elevation angles and is structured to reflect common GEO and non-GEO satellite architectures. Whilst the tool is quite detailed and accurate, in a real commercial system design, further detail is required - transceivers, modems, additional impairments, power amplifier non-linearity and intermodulation, interference, emission regulations, geographical map rain data, and application specific modulation or multi-carrier and bandwidths, and of course cost and practical AIT support in the design. Building complete engineering models is something I do all the time for clients.

Parameters
Satellite Altitude (km) Annual Availability (%)
Elevation A>Sat (deg) Elevation B>Sat (deg)
Slant Range (km) Slant Range (km)

Link A → B
Uplink (A → Satellite)
Uplink Frequency (MHz)
TX Power (dBm)
TX Antenna Gain (dBi)
TX EIRP (dBW)
Clear Sky? (Uplink)
FSPL (dB)
Atmospheric Loss (dB)
Rain Loss (dB)
Polarisation Loss (dB)
Scintillation Loss (dB)
Cloud Loss (dB)
C/N₀ Uplink (dB-Hz)
C/N Uplink (dB)
Satellite Transponder
RX Power Input (dBm)
RX Antenna Gain (dBi)
Noise Figure (dB)
Sky Temperature (K)
G/T (dB/K)
Gain (AGC) (dB)
Saturated Power (dBm)
Output Back-Off (dB)
TX Antenna Gain (dBi)
TX EIRP (dBW)
Downlink (Satellite → B)
Downlink Frequency (MHz)
Clear Sky? (Downlink)
FSPL (dB)
Atmospheric Loss (dB)
Rain Loss (dB)
Polarisation Loss (dB)
Scintillation Loss (dB)
Cloud Loss (dB)
Sky Temperature (K)
RX Antenna Gain (dBi)
RX Power Input (dBm)
RX Noise Figure (dB)
G/T (dB/K)
C/N₀ Downlink (dB-Hz)
C/N Downlink (dB)
Analog
Noise BW (kHz)
C/N₀ Total (dB-Hz)
C/N Total (dB)
Digital
Roll-Off Factor (α)
Symbol Rate (ksps)
Bandwidth (kHz)
Coded Bit Rate (kbps)
Info Bit Rate (kbps)
Modulation
Coding Rate
Coding Gain (dB)
Implementation Loss (dB)
Required Eb/N0 (dB)
Achieved Eb/N0 (dB)
Fade Margin (dB)
Link B → A
Uplink (B → Satellite)
Uplink Frequency (MHz)
TX Power (dBm)
TX Antenna Gain (dBi)
TX EIRP (dBW)
Clear Sky? (Uplink)
FSPL (dB)
Atmospheric Loss (dB)
Rain Loss (dB)
Polarisation Loss (dB)
Scintillation Loss (dB)
Cloud Loss (dB)
C/N₀ Uplink (dB-Hz)
C/N Uplink (dB)
Satellite Transponder
RX Power Input (dBm)
RX Antenna Gain (dBi)
Noise Figure (dB)
Sky Temperature (K)
G/T (dB/K)
Gain (AGC) (dB)
Saturated Power (dBm)
Output Back-Off (dB)
TX Antenna Gain (dBi)
TX EIRP (dBW)
Downlink (Satellite → A)
Downlink Frequency (MHz)
Clear Sky? (Downlink)
FSPL (dB)
Atmospheric Loss (dB)
Rain Loss (dB)
Polarisation Loss (dB)
Scintillation Loss (dB)
Cloud Loss (dB)
Sky Temperature (K)
RX Antenna Gain (dBi)
RX Power Input (dBm)
RX Noise Figure (dB)
G/T (dB/K)
C/N₀ Downlink (dB-Hz)
C/N Downlink (dB)
Analog
Noise BW (kHz)
C/N₀ Total (dB-Hz)
C/N Total (dB)
Digital
Roll-Off Factor (α)
Symbol Rate (ksps)
Bandwidth (kHz)
Coded Bit Rate (kbps)
Info Bit Rate (kbps)
Modulation
Coding Rate
Coding Gain (dB)
Implementation Loss (dB)
Required Eb/N0 (dB)
Achieved Eb/N0 (dB)
Fade Margin (dB)

Output Parameter Accuracy by Frequency Range and Model Type

Freq Range Dominant Effects Model Class Sensitivity Tsky Acc (dB) Rain Acc (dB) Cloud Acc (dB) Scint Acc (dB) Net G/T, C/N0 Acc (dB) Primary Error Drivers
<300 MHz Galactic noise Power-law sky Low ±2–3 ~0 ~0 ~0 ±2–3 Antenna beam, ground spillover
300 MHz–1 GHz Galactic → transition Empirical blend Low ±2 ~0 ~0 ~0 ±1–2 Local noise, sidelobes
1–3 GHz Minimum sky noise Const / weak elev Low ±1–2 ~0 ~0 <±0.2 ±1 Receiver NF, losses
3–10 GHz Weak atm + rain (high end) Eng. gas + elev Moderate ±1 ±0.5–1.5 ±0.2–0.8 ±0.2–0.5 ±1 Rain onset, elevation
10–18 GHz Atm + rain dominant ITU parametric High ±1 ±1–3 ±0.5–1.5 ±0.3–0.8 ±1–2 CS / ±2–4 fade Rain-rate statistics
18–30 GHz H2O + rain/cloud Full ITU pref. Very high ±1–2 ±2–5 ±1–3 ±0.5–1.0 ±1–2 CS / ±3–6 fade Humidity, rain model
30–60 GHz Strong gas + weather Radiative transfer Extreme ±1 (full) ±3–8 ±2–6 ±0.8–1.5 ±2–3 CS / ±5–10 fade Absorption lines, clouds
>60 GHz O2 absorption Full ITU only Extreme ±1 ±5–10 ±3–8 ±1–2 ±3 CS / ±8–15 fade Weather statistics dominate