User:Neutronstar2/Harmonic radar

Harmonic radar is a radar princple, whereby the second of third harmonic of a transmitted radar frequency is detected. It was developed for a range of uses, for e.g., as the radar of the GermanV-2 rocket, for detecting people in avalanches, insect tracking radar, automatic vehicle distance keeping, theft protecting, non-linear junction detector to find electronic bugs and military radar to find hidden metallic objects (METRRA/SAR, Metal Re-radiation Radar/Synthetic Aperture Radar).

The basic principle is that every semiconductor element and therefore every metal-metal oxide compound behaves in a non-linear fashion, converting an incident microwave signal into the second or third harmonic frequency and re-emits it. For example, there are theft tags based on this principle consisting of a small vapor-deposited antenna with a semiconductor diode between the two antenna branches. The antennas can pick up a doubling of the frequency of the transmitted microwave signal is detected and an alarm is triggered. A portable radar can also be used to track ground beetles with a glued-on diode or to find buried avalanche victims who are carrying a special ski pass with a diode.

Since the range of this radar principle is only a few meters, it has only become established for special tasks or is only used for research purposes (e.g. beetle radar). In contrast to other radar principles, harmonic radar only provides direction information and no distance information. The RECCO avalanche victim and missing person location 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, KTH Royal Institute of Technology, 1981.
 * Verräterische Schleppe. Mit einem neuartigen Ortungssystem erforschen Wissenschaftler das Leben eines kanadischen Schmetterlings. Der Spiegel (1997) 8, 186.