Calculator Inputs
Formula Used
This calculator uses a practical weighted-environment model. First, it estimates a beam-weighted scene temperature from sky, atmosphere, ground, and target contributions:
T_scene = Σ(wᵢ × Tᵢ)
It then applies radiation efficiency and antenna physical temperature:
T_A = η_r × T_scene + (1 - η_r) × T_phys
Feed or line loss ahead of the receiver is modeled as:
L = 10^(Loss_dB / 10) T_loss = (L - 1) × T_line T_sys = T_A + T_loss + L × T_rx
Thermal noise power is then computed from:
P_n = k × T_sys × B
G/T is reported as:
G/T = G_dBi - 10 × log10(T_sys)
How to Use This Calculator
- Enter representative temperatures for sky, atmosphere, ground, and your observed target.
- Set beam fractions that describe how much of the antenna pattern sees each source.
- Keep auto-normalize enabled unless your percentages already total exactly 100.
- Enter radiation efficiency, antenna physical temperature, receiver temperature, and feed loss.
- Add bandwidth and antenna gain to estimate noise power and G/T.
- Press calculate to show the result above the form, inspect the Plotly graph, and export CSV or PDF files.
Example Data Table
| Scenario | Scene Temp (K) | Antenna Temp (K) | System Temp (K) | Noise Power (dBm) | G/T (dB/K) |
|---|---|---|---|---|---|
| Deep-Space Dish | 61.60 | 72.77 | 144.61 | -117.00 | 14.40 |
| Microwave Radiometer | 145.00 | 160.00 | 362.11 | -103.01 | -1.59 |
| Low-Elevation Link | 134.00 | 152.72 | 350.47 | -106.16 | -6.45 |
Frequently Asked Questions
1) What is antenna temperature?
Antenna temperature is the equivalent noise temperature seen by the antenna from its surroundings and target. It is a radiometric noise metric, not a thermometer reading for the structure itself.
2) Is antenna temperature the same as physical temperature?
No. Physical temperature describes how hot the antenna hardware is. Antenna temperature describes received thermal noise from sky, atmosphere, ground, target emission, and passive losses.
3) Why do beam fractions matter?
Beam fractions describe how much of the antenna pattern views each thermal source. More spillover toward warm ground usually raises antenna temperature faster than extra view toward cold sky.
4) When should I enable auto-normalize?
Enable it when your beam fractions are relative weights rather than exact percentages. It rescales them to 100%, which keeps the weighted scene temperature physically meaningful.
5) Why does feed loss increase system temperature?
Any passive loss before the receiver attenuates desired signal and adds its own thermal noise. Even modest line loss can noticeably increase input-referred system temperature.
6) What is the difference between receiver and system temperature?
Receiver temperature models internal receiver noise. System temperature combines antenna temperature, passive loss noise, and receiver noise into one overall sensitivity figure.
7) Why is bandwidth included in the calculation?
Thermal noise power grows with bandwidth because P = kTB. Wider bandwidth generally increases detected noise power, even when system temperature stays unchanged.
8) What does G/T tell me?
G/T is antenna gain divided by system temperature, usually expressed in dB/K. Higher G/T usually means a more sensitive receiving system with better link performance.