Antenna Current Optimization for Lossy Media With Near-Field Constraints

Optimization of the current distribution is used to analyze how small antennas are affected by amplitude constraints on the near field and by lossy background media. The optimal antenna current that minimizes the stored energy, for a prescribed radiated field in a given direction, and with limited near field in a set of control points, is formulated as a convex optimization problem. The analysis is also extended to antennas in lossy media by using a frequency-derivative approximation of the stored energy. The results suggest that many fundamental antenna problems involving near-field constraints and lossy background media can be analyzed using convex optimization.