The F-22 Raptor and F-35 Seem Almost Invincible. How are they Vulnerable

It is a well-known fact within Pentagon and industry circles that low-frequency radars operating in theVHF and UHF bands can detect and track low-observable aircraft. It has generally been held that such radars can’t guide a missile onto a target—i.e. generate a “weapons quality” track. But that is not exactly correct—there are ways to get around the problem according to some experts.

byDave Majumdar

With a missile warhead large enough, the range resolution does not have to be precise. For example, the now antiquated S-75 Dvina—known in NATO parlance as the SA-2 Guideline—has a 440-pound warhead with a lethal radius of more than 100 feet. Thus, a notional twenty-microsecond compressed pulse with a range resolution of 150 feet should have the range resolution to get the warhead close enough—according to Pietrucha’s theory.

The United States has poured ten of billions of dollars into developing fifth-generation stealth fighters such as the Lockheed Martin F-22 Raptor and F-35 Joint Strike Fighter. However, relatively simple signal processing enhancements, combined with a missile with a large warhead and its own terminal guidance system, could potentially allow low-frequency radars and such weapons systems to target and fire on the latest generation U.S. aircraft.

(This first appeared in 2017.)

It is a well-known fact within Pentagon and industry circles that low-frequency radars operating in theVHF and UHF bands can detect and track low-observable aircraft. It has generally been held that such radars can’t guide a missile onto a target—i.e. generate a “weapons quality” track. But that is not exactly correct—there are ways to get around the problem according to some experts.

Traditionally, guiding weapons with low frequency radars has been limited by two factors. One factor is the width of the radar beam, while the second is the width of the radar pulse—but both limitations can be overcome with signal processing.

The width of the beam is directly related to the design of the antenna—which is necessarily large because of the low frequencies involved. Early low-frequency radars like the Soviet-built P-14 Tall King VHF-band radars was enormous in size and used a semi-parabolic shape to limit the width of the beam. Later radars like the P-18 Spoon Rest used a Yagi-Uda array—which were lighter and somewhat smaller. But these early low frequency radars had some serious limitations in determining the range and the precise direction of a contact. Furthermore, they could not determine altitude because the radar beams produced by these systems are several degrees wide in azimuth and tens of degrees wide in elevation.