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the EHF band causes unacceptable radiation hazards to personnel. |
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the attenuation caused by precipitation is greater in the EHF band and reduces the radar's effective range and usefulness. |
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the EHF band is not suitable for the provision of the very narrow beams needed for an ASMI radar. |
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target discrimination using the SHF band is better. |
| Explaination:
The EHF band is not suitable for an ASMI radar as the degree of attenuation in most types of precipitation reduces its effective operational range and capabilities. Radar energy is absorbed and scattered by raindrops; the total effect depends upon the size of the water droplets and the transmitted wavelengths. At wavelengths longer than 10 cm the attenuation is negligible. If the wavelength is between 10 cm and 4 cm the attenuation is significant only in tropical rain. However, with wavelengths less than 4 cm attenuation is significant in rain in the temperate latitudes. One conclusion is that wavelengths less than 3 cm should not be used for long range systems. Airfield Surface Movement Indicator (ASMI) radars operate at 1.75 to 2 cm wavelengths. Airborne Weather Radars (AWR) and Precision Approach Radars (PAR) use 3 cm wavelengths. Surveillance radars (ground) use 10, 23 or 50 cm wavelengths. |
