Low-frequency radar is
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
which uses frequencies lower than 1 GHz such as L-band, UHF, VHF, and HF, as opposed to the usual radar bands, which range from 2 GHz to 40 GHz.The
radar cross section
Radar cross-section (RCS), also called radar signature, is a measure of how detectable an object is by radar. A larger RCS indicates that an object is more easily detected.
An object reflects a limited amount of radar energy back to the source. ...
of any target depends on the frequency transmitted by the radar. Below 900 MHz the target radar cross section increases exponentially, however the increased radar cross section means that there is also much more radar return from undesirable sources, such as
cloud cover
Cloud cover (also known as cloudiness, cloudage, or cloud amount) refers to the fraction of the sky obscured by clouds on average when observed from a particular location. Okta is the usual unit for measurement of the cloud cover. The cloud c ...
and
rain
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
(''cf.''
weather radar
Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pulse- ...
). It is because of this that radars traditionally use much higher frequencies, with an exception being the radars operated in the 3-30 MHz band which are used as
over-the-horizon radar stations because signals in that range are able to
reflect off the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...
.
Recent interest has accumulated in developing radars which operate in these low frequencies to help counter the advancement in
stealth technology
Stealth technology, also termed low observable technology (LO technology), is a sub-discipline of military tactics and passive and active electronic countermeasures, which covers a range of methods used to make personnel, aircraft, ships, su ...
by applying advanced
digital signal processing
Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...
to these bands in order to reduce radar clutter. If the radar wavelength is roughly twice the size of the target, a half-wave resonance effect can still generate a significant return. However, low-frequency radar is limited by shortage of unused frequencies, lack of accuracy given the long wavelength, and by the radar's size, making it difficult to transport and making for an easy target. A long-wave radar may detect a target and roughly locate it, but not identify it, and the location information lacks sufficient weapon targeting accuracy
{{DEFAULTSORT:Low-Frequency Radar
Radar