Typically, that resonance effect 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. That means that stealthy tactical fighters will show up on radars operating at a lower frequency bands—such as parts of the S or L band or even lower frequencies. Larger stealth aircraft such as the Northrop Grumman B-2 Spirit or forthcoming B-21 don’t have many of the airframe features that cause a resonance effect—and are, as such, much more effective against low-frequency radars.
While it is true that a layered and integrated air defense may effectively render large swaths of airspace too costly—in terms of men and materiel—to attack using conventional fourth generation warplanes such as the Boeing F/A-18E/F Super Hornet or Lockheed Martin F-16 Fighting Falcon, these systems have an Achilles’ Heel. Russian air defenses will still struggle to effectively engage fifth-generation stealth aircraft such as the Lockheed Martin F-22 Raptor or F-35 Joint Strike Fighter.
“In terms of establishing viable air defenses against opponents with fifth generation aircraft, it’s quite clear how Russia is trying to tackle the problem of stealth,” said Mike Kofman, a research scientist specializing in Russian military affairs at CNA Corporation during an interview with The National Interest. “Russia’s advanced radar, variety of capable missiles and systems that try to integrate large amounts of data for a more potent air defense will increasingly segregate Western air forces into two benches. In a future where these systems have proliferated to China, Iran and other regional powers there will be those that can penetrate and survive against advanced air defenses in a high end fight, and those whose job it is to bomb ISIL or its successor.”
(Note: This first appeared in 2016.)
Kofman notes that advanced Russian-built air defenses like the S-300, S-400 and forthcoming S-500 family come with systems designed to detect and track the presence of low observable (LO) aircraft such as the F-22 and F-35. That’s just a function of physics, as I have noted before. The problem for Moscow is that while Russian early warning and acquisitions radars operating in the VHF, UHF, L and S bands can detect and even track a tactical fighter-sized stealth aircraft, those systems don’t deliver a weapons quality track. “Russia has invested in low-band early warning radars, with some great variants out there, but can it use these to put a good picture together, and process it to develop a track against low-observation aircraft?” Kofman asked rhetorically.