Harmonic radar
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Harmonic radar is a radar principle in which the second or third harmonic of a transmitted radar frequency is detected and which was developed for different purposes, e.g. B. as radar for the German V2 rocket , avalanche victim radar , beetle and frog tracking radar, car distance radar, theft sensor, mini spy detector (NLJD, non-linear junction detector) and military radar for hidden metallic objects (METRRA, Metal Reradiation Radar).
The basic principle is based on the fact that every semiconductor element and therefore every metal-metal oxide connection (rusty nail) behaves as a non-linear element that converts an incident microwave signal into double or triple frequency and then radiates it again. So exist z. B. the theft tags based on this principle from a small vapor-deposited antenna with a semiconductor diode between the two antenna branches. When passing through a special barrier, the doubling of the frequency of the transmitted microwave signal is detected and an alarm is triggered. Ground beetles with a glued-on diode can also be tracked with a portable radar , or avalanche victims who have been buried and carry a special ski pass with a diode can be found.
Since the range of this radar principle is only a few meters, it has only established itself for special tasks or is only used for research purposes (e.g. beetle radar). In contrast to other radar principles, the harmonic radar only provides directional information and no distance information. The RECCO avalanche search system works according to this principle.
literature
- Peter Fuks: Harmonic Radar, a modern method for location of avalanche victims. Akademisk avhandling, Report Trita-Tet-8101, Royal Stockholm University of Technology , 1981.
- Treacherous train. Scientists are researching the life of a Canadian butterfly with a novel positioning system. Der Spiegel (1997) 8, 186.