A lot of folks equate “stealth” with complete invisibility and that is simply not the case. Any aircraft with what we call LO or “Low-Observable” features can be seen by radar. It simply depends on the conditions in which the aircraft is operating, and what systems are attempting to locate it. So while we’re not here to give away our secrets or reveal sensitive capabilities of our 5th-Generation aircraft, it does help to know what the other side is working on to try to negate our nation’s LO capabilities.
State-run Chinese media is claiming that the People’s Liberation Army has been able to track the U.S. Air Force’s Lockheed Martin F-22 Raptor stealth fighters over the East China Sea. While the Chinese report might be easily dismissed as propaganda—it is not beyond the realm of possibility. In fact—it’s very possible that China can track the Raptor. Stealth is not a cloak of invisibility, after all. Stealth technology simply delays detection and tracking.
First off, if a Raptor is carrying external fuel tanks—as it often does during “ferry missions”—it is not in a stealth configuration. Moreover, the aircraft is often fitted with a Luneburg lens device on its ventral side during peacetime operations that enhances its cross section on radar.
That being said, even combat-configured F-22s are not invisible to enemy radar, contrary to popular belief. Neither is any other tactical fighter-sized stealth aircraft with empennage surfaces such as tailfins—the F-35, PAK-FA, J-20 or J-31. That’s just basic physics.
The laws of physics essentially dictate that a tactical fighter-sized stealth aircraft must be optimized to defeat higher-frequency bands such the C, X, Ku and the top part of the S bands. There is a “step change” in a Low Observable (LO) aircraft’s signature once the frequency wavelength exceeds a certain threshold and causes a resonant effect. Typically, that resonance occurs when a feature on an aircraft—such as a tail-fin — is less than eight times the size of a particular frequency wavelength. Effectively, small stealth aircraft that do not have the size or weight allowances for two feet or more of radar absorbent material coatings on every surface are forced to make trades as to which frequency bands they are optimized for.
Therefore, a radar operating at a lower-frequency band such as parts of the S or L band—like civilian air traffic control (ATC) radars—are almost certainly able to detect and track tactical fighter-sized stealth aircraft. However, a larger stealth aircraft like the Northrop Grumman B-2 Spirit, which lacks many of the features that cause a resonance effect, is much more effective against low-frequency radars than, for example, an F-35 or F-22. Typically, however, those lower-frequency radars do not provide what Pentagon officials call a “weapons quality” track needed to guide a missile onto a target. “Even if you can see an LO [low observable] strike aircraft with ATC radar, you can’t kill it without a fire control system,” an Air Force official had told me.
That being said, Russia, China and others are developing advanced UHF and VHF band early warning radars that use even longer wavelengths in an effort to cue their other sensors and give their fighters some idea of where an adversary stealth aircraft might be coming from. But the problem with VHF and UHF band radars is that with long wavelengths come large radar resolution cells. That means that contacts are not tracked with the required level of fidelity to guide a weapon onto a target. As one U.S. Navy officer rhetorically asked, “Does the mission require a cloaking device or is it OK if the threat sees it but can’t do anything about it?”