All current stealth aircraft were designed to counter X-Band radars, but those shapes are getting ineffective if a radar operates in S-band and even more ineffective when the radar operates in L-band. The reason for the stealth aircraft to be detected is the wavelength of the radar, a radar operating in L-band produces wavelengths with comparable size to the aircraft itself and should exhibit scattering in the resonance region rather than the optical region, so that most of the existing stealth aircraft will turn from invisible, to visible.
Disadvantages of long wavelength radars
Actually a low frequency radar, comparable in size to a normal X-Band radar has very poor resolution, to fix this problem the low frequency radar must be built as large as possible to allow an engagement, however this only works on ground based radar stations and is problematic on aircraft, the accuracy of those radars is also inferior to normal radars, the frequency must be higher to get a lock with a missile, so that precision targeting cannot be done like on X-Band radars.
In Air to Air combat L-band using radar can be easily detected using passive detection, long before it will be able to track the enemy.
The US Department of Defence made the following statement: “The Northrop-Grumman B-2A 'Batwing' is sufficiently large that its shaping remains effective against lower band radars. The same is not true for fighters with LO shaping“, in fact this means that large stealth planes are still stealthy against low band radars, but Fighters with LO (Low Observable) shaping (alias F-35 Lightning II) are not stealthy enough to remain invisible against those radar systems.
The same does not go for Very Low Observable (VLO) aircraft, as seen in the Ausairpower statement made by Dr. Carlo Kopp: “Low band radars are not a panacea for the defeat of VLO (Very Low Observable) aircraft. Their angular accuracy has been until recently poor, and the required antenna size results in ungainly systems which are usually slow to deploy and stow, even if designed from the outset for mobility. The size and high power emissions of these radars, in types with limited mobility, makes them much easier to detect and destroy than typical mobile systems operating in the decimetric and centimetric bands, which can relocate rapidly after a missile shot.”
This statement means that low band radars are not an Ideal solution against VLO aircraft, because to detect them the radar stations must be very, very large and much to large to be mounted on an aircraft, so that the L-Band radars on the Sukhoi PAK-FA are actually useless, everything they would do at the end is letting a listening F-22 (or F-35) knowing that there´s a PAK-FA somewhere. They are also unable to provide target guidance for the weapons without being ungainly large, that’s the reason for those massive antennas on the ground based radar stations, to get at least a bit of accuracy.
To conclude, here are the general disadvantages of low band radars in shortened form:
- They are unable to provide weapon guidance because of bad resolution and accuracy
- They need to be ungainly large to track an aircraft accurately
- When mounted on aircraft, they are too small to track something or to get a lock on, everything that would happen at the end is letting the enemy know that there´s something out there
But in reality, the L-Band radars of PAK-FA are primarily used for friend-or-foe identification and electronic warfare, not target acquisition directly. Although the data will be used in the final data processing/analysis, whenever available.
The general advantages of low band radars in shortened form:
- Large UHF, S and L-band radars usually serve as early warning for other higher band radars.
- If linked to other radar stations (both ground based and airborne), this can provide very effective means for early target acquisition. Using an array of different radar bands for triangulation and scanning "suspect regions".
- Small L-Band radars can be useful for electronic warfare, friend-or-foe identification, decoy and illumination.