Low-frequency radar

Low Frequency Radar is the use of radars which use frequencies lower than 1 GHz, as opposed to the usual Radar bands which can range from the X band at 8-12 GHz to the Ka band which tops out at 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.

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'. 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