The fact is that no ‘stealth plane’ is immune to detection from all wavelengths. The problem becomes one of the resolution of detection. With enough locators with the right areas of coverage and coordination can locate platforms that are supposed to be stealthy.
These low frequency arrays have been around for a long time. Often used for OTH and the odd use. The fact is that stealth planes are optimized for expected RF locator sources. That usually means from head-on incursion angles. Detection from underneath, or overhead (think satellites my friends) and the game gets trickier.
The truth is that stealth is for use against non sophisticated targets. They are not invulnerable from passive systems using ubiquitous sources, nor are they completely radar invisible. To believe ‘stealth’ is the panacea is foolish.
Don’t forget that the lower the return signal from the stealthy target, the higher gain required by the receiver to reliably detect a signal. This also makes such radar more susceptible to jamming, and the jamming signal doesn’t need to be as powerful, making jamming pods smaller.
It would also be fairly easy to deploy decoys that could passively or actively emulate a larger target in the lower frequencies, further complicating any attempted intercept.
“First Secretary, the infrared guidance system is not the most accurate means of aiming. It may be necessary for a Soviet aircraft to act as a target. Will you give that order?”
(Pause)...”Of course.”
“Very well, First Secretary, then the American is bound to fly into our trap.”