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It has been demonstrated that modifying the rim scattering of a paraboloidalreflector antenna through the use of reconfigurable elements along the rimfacilitates sidelobe modification including cancelling sidelobes. In this workwe investigate techniques for determining unit-modulus weights (i.e., weightswhich modify the phase of the scattered electric field) to accomplish sidelobecancellation at arbitrary angles from the reflector axis. Specifically, it isshown that despite the large search space and the non-convexity of the costfunction, weights can be found with reasonable complexity which providesignificant cancellation capability. It is demonstrated that this can be doneusing open-loop (i.e., with pattern knowledge), closed-loop (without patternknowledge), or hybrid (with inexact pattern knowledge) techniques. Initially,we examine the use of unconstrained weights. A primary finding is thatsufficiently deep nulls are possible with essentially no change in the mainlobe with practical (binary or quaternary) phase-only weights. The initialalgorithms require a knowledge of the antenna pattern (what we term an``open-loop'' approach). However, since perfect knowledge of the pattern is nottypically available, we also develop closed-loop approaches which require noknowledge of the antenna pattern. It is found that these closed-loop approachesprovide similar performance. We demonstrate the time-varying performance ofclosed-loop approaches by simulating an interfering source which moves acrossthe field of view of the antenna. Finally, we leverage the advantages of bothopen-loop and closed-loop approaches in a hybrid technique that exploitsinexact knowledge of the pattern by seeding a closed-loop optimization with anopen-loop solution as its starting point.

Open and Closed-Loop Weight Selection for Pattern Control of Paraboloidal Reflector Antennas with Reconfigurable Rim Scattering