September 13, 2013
Credit: Bill Sweetman/AWST
Even when stealth technology was deadly secret and the F-117A did not officially exist, there was counter-stealth radar.
Textbooks told us radar cross-section (RCS) was frequency dependent, and tended to become increasingly so as the target shape grew more complicated. If the radar wavelength is of the same magnitude as prominent features of the target, the signal is scattered by a resonant mechanism that is unimpressed by cunning shaping or materials magic. In the 1980s, many older Russian systems operated in the VHF band, with wavelengths in the 1-2-meter range, which is about the same as the chord of a fighter’s tail surfaces and wingtips.
But, as I wrote in 1987:
“The price of increasing wavelength . . . is that the antenna has to grow in proportion to the wavelength in order to maintain a narrow beam and adequate resolution. The ‘mobile’ Soviet VHF radars are cumbersome, and early-warning radars such as Tall King (P-14) are large fixed structures and provide coverage of only one sector. Despite the size of their antennae, they are not accurate enough to manage a complete engagement.”
The Pentagon’s then-stealth technology director, Paul Kaminski, commissioned an aggressive Red Team in the very early 1980s that had both recognized the threat from VHF radars and discerned that it could be mitigated by artful mission planning. The Red Team’s work led to the development of the computer-driven route planner that F-117 pilots, fond of a vampish TV horror-movie hostess, nicknamed Elvira.
The same assessments applied when the requirements for the F-35 Joint Strike Fighter (JSF) were written in the mid-1990s. There are no signs that the raw RCS of the F-22 or JSF is much smaller than that of the F-117. The goals were to improve aircraft performance and maintainability, neither of which (to put it very mildly, indeed) was the F-117’s long suit. If you want a very low RCS in VHF, you need to lose the tails, which is why the B-2 is a flying wing.
It wasn’t hard for the Russians to assess the JSF’s stealth performance. By 1995, everyone knew that shape was the major driver of RCS, with materials being used to control local scattering phenomena. As the JSF’s target service entry date arrived, so did the Russian answer, and it was on display at the MAKS air show, held in Moscow in August.
The 55Zh6ME radar complex addresses many of the limitations of the old VHF radars. Although you see three radars—stepping down from VHF (metric) to L-band (decametric) and S-band (centimetric)—the Russians call them modules of an integrated radar system. Each unit is fitted with the Orientir satellite-navigation system, which provides a very accurate location and north reference. That should make it possible to provide sensor fusion—ensuring that when two or more of the radar units detect a target, it will show up as one in the control center.
The VHF part of the system (see photo) has a P-14-sized, 30-meter-wide antenna, but it folds onto an 8 x 8 truck. The antenna has an active, electronically scanned array, so if it gets a hit on a faint target, the array can dwell on it as the antenna rotates (or swings back and forth for a sector search). At the same time, it will cue its L-band and S-band sisters to focus on the target area like searchlight beams.