EM wave 一問

It is because all objects, as long as it is not at -273.15 C (absolute zero degree), will emit infra-red radiation. So, it radar use infrared to detect aircraft, then the sensor will have problems in distinguishing the infrared radiation from the aircraft or the background radiation.

So, microwave is used instead of infrared.

Also, microwave have low frequency and long wavelength. This makes microwave cannot penerate the atmosphere so easily. So, loss of radiation can be reduced. (Short wavelength radiation such as ultra-violet can penerate atmosphere so easily.)