Structure of the EMS
The electromagnetic spectrum is the complete range of EM radiation, ordered from low to high frequency (and therefore from long to short wavelength). The boundaries between the regions are conventions, not hard physical transitions:
| Region | Frequency | Wavelength | Military relevance |
|---|---|---|---|
| Radio waves | 3 Hz – 300 GHz | 100,000 km – 1 mm | communication, radar, navigation, EW |
| Infrared (IR) | 300 GHz – 394 THz | 1 mm – 760 nm | thermal imaging, heat-seeking missiles |
| Visible light | 394 – 789 THz | 760 – 380 nm | optical sensors, cameras, laser |
| Ultraviolet (UV) | 789 THz – 30 PHz | 380 – 10 nm | missile plume detection (missile warning) |
| X-rays | 30 PHz – 30 EHz | 10 nm – 10 pm | medical/industrial, not used for sensors |
| Gamma rays | > 30 EHz | < 10 pm | nuclear detection |
Two trends run through the entire spectrum and explain many sensor choices:
- The higher the frequency, the more precisely you can measure and the smaller the antenna or optics can be — but also the more you suffer from attenuation by the atmosphere, rain and fog.
- The lower the frequency, the further the signal reaches and the better it gets through obstacles and weather — but at the expense of accuracy and with larger antennas.
Key point
There is no "best" frequency. Every sensor type is a compromise between range, accuracy, size and weather sensitivity. Military applications within the EMS works this out per frequency region.