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Low-frequency radar is radar which 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 it is highly effective against stealth aircraft, stealth ships, etc. pending clutter can be reduced.
Recent interest has accumulated 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 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