A versatile adaptive array for LINK-11 communications

LINK-11 is an automated, one- or two-way, HF data link to distribute information within the Navy Tactical Data System. The null out, beam up, and lock on LINK-11 (NOBULL-11) adaptive antenna array (AAA) was developed to reduce the effects of cochannel interference on LINK-11 communications. The authors describe the NOBULL-11 AAA and performance results obtained during testing of the system with a rooftop antenna array. The NOBULL-11 adaptive algorithm operates without knowledge of the LINK-11 signal angle-of-arrival or network timing, and overcomes two significant limitations associated with adaptive arrays: poor rejection of interferences at the same incident power level as the desired signal and accidental nulling of a protected desired signal. It does this with knowledge only of fundamental LINK-11 signal characteristics. The key to the success of the NOBULL-11 AAA is its ability to maintain nulls on interference as the interference scenario changes. Overall, the laboratory tests of the NOBULL-11 AAA were favorable, and indicated that the AAA can provide signal-to-interference (S/I) enhancements of 45 to 15 dB over a wide range of S/I ratios