What is the antenna temperature and how does it relate to the noise performance of a receiving system?
Antenna Noise Temperature
Every object at a physical temperature above absolute zero radiates electromagnetic noise. When the antenna's radiation pattern illuminates these objects, their thermal radiation enters the antenna and appears as noise power at the receiver input. The antenna temperature Ta quantifies this received noise as an equivalent temperature at the antenna output terminals.
| Parameter | Low Gain | Medium Gain | High Gain |
|---|---|---|---|
| Gain Range | 2-6 dBi | 6-15 dBi | 15-45 dBi |
| Beamwidth | 60-360° | 15-60° | 1-15° |
| Typical Types | Dipole, monopole, patch | Yagi, helical, horn | Parabolic, array, Cassegrain |
| Bandwidth | Narrow to wide | Moderate | Narrow to moderate |
| Complexity | Low | Medium | High |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
Frequently Asked Questions
What is a typical antenna temperature?
Zenith-pointing Earth station at C-band: Ta = 15-25 K. At Ka-band (clear sky): Ta = 30-80 K. Low-elevation angle (antenna sees trees/buildings through sidelobes): Ta = 50-100 K. Horizonal antenna seeing the ground: Ta = 200-290 K.
How does rain affect antenna temperature?
Rain absorbs and re-radiates at its physical temperature (≈ 280 K). In heavy rain: the antenna temperature can increase by 100-200 K at Ka-band, significantly degrading G/T and receiver sensitivity. The rain attenuation and noise increase combine to create a double penalty.
How do I measure antenna temperature?
Use a Y-factor measurement: compare the receiver output power when the antenna alternately views a hot calibration source (known temperature, e.g., ambient absorber at 290 K) and the cold sky (known temperature, e.g., 10 K at zenith). The ratio gives the system noise temperature, from which Ta is extracted.