Reduced Order Jammer Cancellation Scheme Based on Double Adaptivity

A doubly adaptive scheme is presented for detection and jammer cancellation by airborne/spaceborne radar equipped with a limited number of receiving channels. In this case where, to guarantee the desired performance in the protection against multiple jammers with a wide range of possible direction of arrivals (DOAs), a number of auxiliary antenna beams greater than the number of channels would be required. For these systems an adaptive auxiliary beam selection technique is proposed to decide which is the most effective subset of auxiliary antennas in each condition, assuming a slowly changing jamming environment. This leads to a doubly adaptive jammer cancellation scheme: we first perform an adaptive selection of the best set of auxiliary beams, and then we apply an adaptive scheme for jammer cancellation and target detection by using only the best set of beams. This especially applies to the case of adaptive radar obtained as a retrofit of existing monopulse radar sensors or of design retrofit for single channel spaceborne radar with a redundant channel. A closed form analytical expression is provided for the detection performance of the proposed reduced degree of freedom (DOF) scheme based on double adaptivity, which provides a complete characterization of the properties of this detection scheme. Based on the derived expression of the detection performance, the proposed scheme is compared with an ideal scheme with a number of channels equal to the number of auxiliary antennas, showing that the proposed approach has near-optimal performance. Finally the implementation issues of the doubly adaptive scheme are discussed, together with its limitations.