Low-frequency radar
Encyclopedia
Low-frequency radar
uses frequencies lower than 1 GHz, as opposed to the usual radar bands, which range from 2 Ghz and up,and the maximum is 40 Ghz.The radar cross section
of any target depends on the radar transmitted frequency. Below 900 MHz the target radar cross section increases exponentially, however the increased radar cross section means that there is much more radar return from undesirable sources, such as cloud cover
and rain
(cf. weather radar
). It is because of this that radars are traditionally at much higher frequency, 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
.
This technology was uncovered by the serbs in kosovo during the Kosovo War in the 1990s. This technology was used to shoot down an F-117 nighthawk via a specially modified anti-aircraft missile to use this radar to guide it towards the target. The serbs say that this radar's drawback is that of the huge amount of clutter it creates because of the sensitivity of this radar. They also say that if you can reduce the clutter, this radar is highly effective against stealth aircraft, stealth ships, etc.
Recently, there has been interest in developing radars which operate in these low frequencies to help counter the advancement in stealth technology
, by applying advanced digital signal processing
to these bands in order to remove much of the "clutter" we talked about earlier. 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 lack of available frequencies which are heavily used by other systems, 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
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
uses frequencies lower than 1 GHz, as opposed to the usual radar bands, which range from 2 Ghz and up,and the maximum is 40 Ghz.The radar cross section
Radar cross section
Radar cross section is a measure of how detectable an object is with a radar. A larger RCS indicates that an object is more easily detected.An object reflects a limited amount of radar energy...
of any target depends on the radar transmitted frequency. Below 900 MHz the target radar cross section increases exponentially, however the increased radar cross section means that there is much more radar return from undesirable sources, such as cloud cover
Cloud cover
Cloud cover refers to the fraction of the sky obscured by clouds when observed from a particular location...
and rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
(cf. weather radar
Weather radar
Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...
). It is because of this that radars are traditionally at much higher frequency, with an exception being the radars operated in the 3-30 MHz band which are used as over-the-horizon radar
Over-the-horizon radar
Over-the-horizon radar, or OTH , is a design concept for radar systems to allow them to detect targets at very long ranges, typically up to thousands of kilometers...
stations because signals in that range are able to reflect
Ionospheric reflection
Ionospheric reflection is a bending, through a complex process involving reflection and refraction, of electromagnetic waves propagating in the ionosphere back toward the Earth....
off the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
.
This technology was uncovered by the serbs in kosovo during the Kosovo War in the 1990s. This technology was used to shoot down an F-117 nighthawk via a specially modified anti-aircraft missile to use this radar to guide it towards the target. The serbs say that this radar's drawback is that of the huge amount of clutter it creates because of the sensitivity of this radar. They also say that if you can reduce the clutter, this radar is highly effective against stealth aircraft, stealth ships, etc.
Recently, there has been interest in developing radars which operate in these low frequencies to help counter the advancement in stealth technology
Stealth technology
Stealth technology also termed LO technology is a sub-discipline of military tactics and passive electronic countermeasures, which cover a range of techniques used with personnel, aircraft, ships, submarines, and missiles, to make them less visible to radar, infrared, sonar and other detection...
, by applying advanced digital signal processing
Digital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
to these bands in order to remove much of the "clutter" we talked about earlier. 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 lack of available frequencies which are heavily used by other systems, 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