RADIO DIRECTION-FINDING

**Definition:** This place covers:

**Glossary:** - Waves: Is the mechanism by which energy is transported without the transfer of matter. Waves may be either electromagnetic waves, which do not require a medium to propagate, or mechanical waves, which require a medium, e.g. acoustic waves. Waves most easily are defined in mathematical terms as obeying a so-called wave equation. - Propagation effects: Are relevant if the outcome of a measurement depends on the actual value of a physical quantity characterising the propagation of the wave, i.e. its wavelength, frequency, velocity, or phase. The mere presence or direction of a wave are not considered a propagation effect or to contribute to a propagation effect. To put it in another way, propagation effects are irrelevant, if the radiation may be looked upon as a beam of radiation whose wave nature can be ignored. Examples of measurements where propagation effects are relevant include e.g. measurements of propagation time, phase difference, phase delay, measurements using the Doppler effect, or interference. - Navigation: Is in this subclass limited to position fixing, or determining the velocity or direction of velocity of vehicles or crafts or their distance from other objects. - Reflection: Means the general physical phenomenon that propagating waves are being scattered by any object, body or target in their path. Scattering can be elastic (i.e. the frequencies of the incoming and outgoing waves are the same) or inelastic (i.e. the respective frequencies are different). Other properties of the wave may change as well. Reflection can be specular or diffuse depending on surface properties of the scattering object. Reradiation further includes the mechanism characteristic of a transponder, i.e. receiving a wave and then transmitting an answering wave. - Transponder: Means an arrangement which reacts to an incoming interrogating or detecting wave by emitting a specific answering or identifying wave. - Active systems: Means systems comprising an artificial source for emitting waves. The propagating waves interact with at least one object and are eventually detected by the system. The interaction may consist in e.g. a reflection. - Passive systems: Means systems detecting waves that are not emitted by the measuring system itself (e.g. by the sun). - Object: An entity that is not part of the measuring device.