Abstract model of any measurable size changing over time, generated by natural phenomena or systems, considered as an information carrier.

Slant polarisation

Type of linear polarisation, at which electric vector vibrations take place diagonally to the reference plane (usually Earth’s surface).

Slow fading

1) Signal fading due to the heterogeneity of the troposphere and the irregular morphology of the terrain along the radio path. 2) Fading arising when the coherence time of the channel is large relative to the delay constraint of the channel.

Smooth earth

The area of such irregularities heights at which the radio wave reflected from the surface of the earth loses its character of a mirror and becoming a dispersion.

Software defined radio

A radio transmitter and / or receiver employing a technology that allows free setting of the RF operating parameters including, but not limited to, frequency range, modulation type, or output power to be set or altered by software.

Space wave

The wave propagating between the transmitting and receiving antenna. Its propagation is not affected by electrical parameters of terrain. It consists of the direct wave and the reflected wave. It is one of the components of the ground wave.


The part of the electromagnetic spectrum corresponding to radio frequencies – that is, frequencies lower than around 3 000 GHz.

Spectrum mask

A mathematically-defined set of lines applied to the levels of radio transmissions. The spectral mask is generally intended to reduce adjacent-channel interference by limiting excessive radiation at frequencies beyond the necessary bandwidth.

Spectrum refarming

The process making for periodic review and redeploying of spectral resources.

Spectrum sensing

Acquisition of information about actual occupancy of radio spectrum, without making influence with the spectrum environment (by measurements).

Spurious emission

Emission on a frequency or frequencies which are outside the necessary bandwidth and the level of which may be reduced without affecting the corresponding transmission of information. Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products, but exclude out-of-band emissions.


1) Guideline documentation that reflects agreements on the requirements to be met by the products, practices, or operations, to be able are considered as functional. 2) Documents formally describing the standards and established in accordance with the applicable procedures.


W języku angielskim termin "standard" dotyczy zarówno polskich: "normy" i "standardu".

Standard atmosphere

An atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes. It has been established to provide a common reference for temperature and pressure and consists of tables of values at various altitudes, plus some formulae by which those values were derived.

Standing wave ratio

Standing wave ratio is a measure of impedance mismatch transmission line (eg coaxial cable) to the load (eg antenna). It is defined by the ratio of the amplitude maximum to minimum amplitude of the voltage standing wave in the antenna feed line.

Surface wave

The wave propagating near the surface of an object or structure (e.g. the Earth's surface). Propagation of this wave strongly depends on the electrical parameters of terrain. In the case of propagation at the surface of the Earth is a component of ground wave.