Command Post
RF transmission and reception de-confliction is a vital element not only in electronic warfare, but also military communications.

DARPA’s WARP RF deconfliction programme moves forward.

The US Defence Advanced Research Projects Agency’s (DARPA) WARP programme aims to provide narrowband sensitivity with wideband performance. The Wideband Adaptive Radio Frequency Protection (WARP) initiative is working to safeguard RF receivers against external and self-interference.

DARPA hopes this will yield techniques allowing wideband radios to be used in electromagnetically contested and congested areas. Wideband receivers are exposed to more signals than their narrowband counterparts. They can experience more accidental and deliberate interference from external sources, and from the RF system the receiver equips.

Stadium Rock

As Mark Hickle, senior principal scientist, and Ryan Wang, technology development manager, at BAE Systems’ FAST Labs told Armada: “Electronic receivers must detect low power signals of interest from adversaries or friendly forces in the presence of unwanted interfering signals which are higher in power by many orders of magnitude.” They describe this situation as akin to “trying to listen to someone whispering at a rock concert.”

Messrs. Hickle and Wang note that “receivers are generally protected from external interference through static filtering, automatic gain control, or signal limiters.” The problem is that “external inferences present in many environments are constantly changing.” Dynamic filtering must be used to continually account for these changes. Furthermore, “automatic gain control degrades sensitivity to low-power signals.” Meanwhile “the use of signal limiters can cause cross-modulation distortion and may decrease the overall sensitivity of the system.”

Self-Interference

Self-interference is also a problem: “Even receive-only systems must often coexist with other transmitters located on the same platform.” To an extent this can be achieved through the physical isolation of transmit and receive channels. This helps prevent high power transmit channels leaking into a receiver optimised for weak signals.

Nonetheless, even physically separating transmit and receive antennas will not always provide sufficient isolation. Thus transmit and receive functions must use different frequencies and time slots for their tasks. WARP is working to allow simultaneous transmission and reception with the same frequency.

DARPA is tackling the problem in two ways: It is working on tuneable filters covering a two gigahertz/GHz to 18GHz spread. These filters will adapt to signals present in these wavebands. The second focuses on self-interference primarily enabling simultaneous transmit and receive functions on a 100 megahertz to six gigahertz waveband.

DARPA awarded BAE systems two WARP contracts in April. The firm is working on the external and internal interference conundrum. It is using “a new type of high-performance chip-scale tuneable filter component.” The company hopes this will meet if not surpass the programme’s requirements. Mr. Hickle, Mr. Wang and their colleagues are “developing sensing and controlling techniques to enable intelligent control of the filters to achieve adaptive interference rejection solutions.” The work performed by the company will reach Technology Readiness Level Four (TRL-4). The US Department of Defence defines TRL-4 as validating the system in a laboratory environment.

BAE Systems continued that the contact will last a minimum of 18 months. It will conclude in 2022. Two optional follow-on phases of work may later be awarded lasting a total of 30 months.

by Dr. Thomas Withington