The anechoic chamber at Lockheed Martin in Fort Worth, Texas, has operated in relative anonymity since its beginning in 1987. During that time, a variety of Lockheed Martin aircraft and aircraft systems, from two versions of the F-111 to many versions of the F-16, have been tested in this electromagnetically clean environment. The latest airframe to be tested in the chamber is an F-35A.
Anechoic chambers are rooms designed to stop reflections of either sound or electromagnetic waves and to isolate the aircraft from outside radio signals. The RF absorbers on the walls, floor, and ceiling inside the chamber prevent stray internal RF reflections created for the testing from bouncing back at the aircraft. The chamber in Fort Worth is used to characterize and confirm radio frequency interactions and cooperative operation of aircraft avionics.
Before the F-35A could be tested in the anechoic chamber, the chamber itself needed to be upgraded. A new 270-volt power generator, a fiber optic-based data acquisition system, and equipment for liquid and air cooling were added. The initial testing on the first F-35 was completed in August 2010. “The upgrades to make the facility F-35 compatible and the test itself went so smoothly that we finished nine days ahead of schedule,” said David Hamre, RF testing lead for the F-35.
During the test, RF antennas on the F-35 used for targeting, navigation, satellite communication, voice communications, data links, environmental awareness, landing, and the like were assessed to determine if they worked cooperatively with the onboard transmitters and receivers with minimal interference.
The testing was performed on F-35A AF-3 because it has fully capable mission systems. The early test versions of the F-35A (AA-1, AF-1, and AF-2), which were used primarily for testing flying qualities, had only partially capable mission systems. Testing on AF-3 included operating the APG-81 radar, electronic warfare system, tactical air navigation system, identification friend or foe system, and the radar altimeter. Not all production F-35s will be put through comprehensive RF testing. After initial tests of the RF systems, follow-on testing will be conducted when the systems are changed significantly.
“The anechoic chamber tests reduce the amount of avionics testing we have to do in flight,” added Hamre, who was the F-16 chamber test lead for twelve years before coming to the F-35 program. “While the chamber will continue to be used for the F-16, this test on F-35 AF-3 marks the beginning of a new era for this facility.”