Fighters set apart by AESA radars

 - December 6, 2006, 11:07 AM

Northrop Grumman’s active electronically scanning array (AESA) radars have undoubtedly made a big impact on fighter technology. The AN/APG-77, the AN/APG-80 and the AN/APG-81 are fitted, respectively, to Lockheed Martin’s F-22A Raptor, F-16E/F Block 60 Desert Falcon, and F-35 Joint Strike Fighter (JSF).

The radar all three of these aircraft use in combat employ almost the same state-of-the-art technology. The AESA technology has become the great equalizer in that it provides a capability that can be fitted to multiple platforms.

This, in turn, gives Lockheed Martin the flexibility to offer customers a “same wine/different bottle” option when selecting a fighter aircraft. “What is important to any potential customer is that deciding to procure a less expensive aircraft that is an older design does not mean that they are buying into a less-capable suite of on-board systems,” a Northrop Grumman spokesman told Aviation International News.

“The AESA radar and what it brings to the aircraft’s combat performance has become the common denominator,” said a Northrop Grumman engineer. “The key is how far we have progressed in the design and manufacturing of the AESA’s transmit and receive [T/R] modules,” he added.

The latest, fourth-generation T/R design was based on the APG-80/81 arrays, but it is also being retrofitted into the APG-77. This means every F-22A from Lot 4 production and beyond will have an AESA built with the same T/R components that are in the F-35 and F-16E/F radar arrays.

The improvements of the AESA design over previous generation radars, such as the APG-68-(V)9, which is the standard radar in previous model F-16s, are substantial. The APG-80/81 series has three times the range of any radar fitted to a current F-16. It incorporates frequency hopping and other processing parameters that create what the designers call a “low probability of intercept” operation. In this way, the AESA radar can detect a target without the target’s electronic warnings systems becoming aware that it is being scanned.

The AESA radars are designed to search continuously for and to track multiple targets within the forward hemisphere of the aircraft. Since each sector on the array is its own transmitter and receiver, the AESA is able to perform an entire range of tasks. It no longer is just a radar, but a multifunctional array. This allows pilots to simultaneously search air-to-air, track those air-to-air targets, process air-to-ground targeting, produce high-resolution synthetic aperture radar imagery, transmit electronic countermeasures (ECM) against enemy radars and also guide the aircraft in a terrain-following mode–and all at much greater detection ranges.

An APG-77 fitted onboard an F-22A has demonstrated the transfer of a 72mb synthetic aperture radar image in 3.5 seconds at a data rate of 274 mbps. This process would have taken 48 minutes using the Link-16 protocol, which is the standard data exchange system in U.S. and NATO equipment.

The negative aspect of the AESA technology is that the hundreds of T/R modules produce a tremendous amount of heat, which requires a liquid cooling system that can be a maintenance headache when trying to use the aircraft operationally. This is offset by the fact that the AESA design enjoys a twofold increase in reliability compared to conventional, mechanically scanned radars, according to Northrop Grumman designers.

One question that remains unanswered is when and how Lockheed Martin will integrate an APG-80 derivative into its Block 50 series F-16C/D, which would make it a “Block 50 double plus” derivative. This seems an inevitable step that the Fort Worth, Texas-based manufacturer will have to take as both its existing customer, Pakistan, and prospective customer, India, have indicated that one of the prime requirements in their next fighter buy is that an AESA be on board.

Having this capability on board a fighter has become the prime consideration in the procurement of new fighters and the modernization of older models. Who flies faster and who turns tighter does not mean so much anymore.