The range of high-frequency (HF) electromagnetic waves covers a frequency spectrum of about seven decades and extends up to the limit of the infrared spectral region (Sub-Terahertz range). Important fields of application of the HF and microwave techniques are, for example:
- telecommunication: radio, television, satellite communication, remote control, point-to-point communication;
- mobile communication (broadband communication systems, wireless local area networks);
- navigation and position-finding techniques, road transport informatics (RTI), automotive obstacle detection, collision avoidance radar;
- remote sensing, surveillance of land, sea, and air, connection to mobile stations in trains, ships, aircrafts;
- medical diagnostics and therapy (detection of foci of diseases, radiation therapy);
- exploration of the earth (mineral resources, cartography), oceanography, meteorology, and environmental monitoring (investigation of the atmosphere, detection of clouds, fog, precipitation, air, and water pollution);
- radio-astronomic investigations; investigation of molecular and atomic structures (reception of HF radiation from space, microwave spectroscopy);
- nuclear fusion technology (plasma diagnostics and generation), particle acceleration;
- dielectric heating (microwave ovens, industrial drying, HF induction melters), chemical process technique, solid-state chemistry.
Modern HF and microwave technique today is characterized by the following prominent features:
- Active and passive semiconductor components for very high frequencies have been developed, such as HF transistors up to 100 GHz, Gunn, IMPATT, amd Schottkydiodes up to more than 100 GHz.
- Signal sources, measuring generators, and frequency synthesizers covering frequency bandwidths from 1 Hz to more than 50 GHz are already commercially available.
- With a new generation of microstructure components, a large number of new civilian and military applications of the microwave technique will be possible.
- HF generators of very high level (a few ten MW pulse output power) or of large frequency bandwidth of up to three octaves are available for modern long-range transmission and radar techniques.
HF and microwave measuring instruments required for quality assurance, research and development are today available in the frequency range extending far beyond 100 GHz, for example:
- to determine the output power of HF generators,
- to measure the attenuation of passive HF components, cables, and transmission lines,
- to characterize HF components in coaxial, waveguide, and planar techniques by determining their scattering (S-) parameters,
- to measure the voltage in coaxial line systems (at frequencies up to a few GHz).