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

TL;DR

This paper develops algorithms for weight selection in reconfigurable rim scattering of paraboloidal reflector antennas, enabling effective sidelobe cancellation and null placement with phase-only weights, using open, closed, or hybrid control methods.

Contribution

It derives general weight formulas for null placement, introduces a phase-only weight technique, and demonstrates practical nulling capabilities with minimal main lobe distortion.

Findings

Nulls can be effectively placed with phase-only weights.

Deep nulls are achievable with minimal main lobe gain change.

Algorithms work with both quantized and unquantized phases.

Abstract

It has been demonstrated that modifying the rim scattering of a paraboloidal reflector antenna through the use of reconfigurable elements along the rim facilitates sidelobe modification including cancelling sidelobes. In this work we investigate several open questions with respect to algorithms for determining the weights. First, we derive the general weight values needed at each reconfigurable element to place nulls at arbitrary angles. Second, since in many cases these weights require gains other than one, we develop a technique for determining unit-modulus weights so as to allow for surfaces which merely modify the phase of the scattered field, while substantially reducing the gain at arbitrary angles. Specifically, it is shown that despite the large search space (and non-convexity in the presence of discrete weights), weights can be found with reasonable computational complexity which provide useful cancellation capability. Third, it is demonstrated that this can be done using open-loop (i.e., with pattern knowledge), closed-loop (without pattern knowledge), or hybrid (with inexact pattern knowledge) techniques both quantized and unquantized phases. A primary finding is that sufficiently deep nulls are possible with essentially no change in the main lobe gain with practical (binary or quaternary) phase-only weights.