Fundamental bounds and optimization of small antennas

Fundamental bounds and optimization of small antennas

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This chapter reviews the use of fundamental bounds and the Q-factor in small antenna optimization. With the fundamental bounds, the antenna designer can estimate how well the antenna will perform before the design process. This can provide insight if the design specifications can be met with the structure at hand. Moreover, knowledge of the antenna's bounds can be used in a physical limitation-aware optimization, where the optimization process can be terminated once the target is achieved with a certain margin. Formulating the bounds as a convex optimization problem offers the flexibility to add additional “convex” constraints with minor effort. Examples of additional constraints include limitations on efficiency, SAR, and the radiation pattern or optimizing the antenna region of embedded antennas. The antenna designer can investigate numerous situations by adding the previous constraints to the original convex problem. The introduction of a method to estimate Q(Z') of antennas from the current distribution computed for a single frequency; the application of fundamental bounds and of the Q(Z') single-frequency estimation method to design cases of three-dimensional radiating structures has not been considered previously in the literature. The results suggest that customized physical bounds, optimum currents, and single-frequency expressions are tools that are useful for antenna design, e.g., to stop an optimization process, assess realizability of specifications, and assess performance of antenna locations. While the examples in this chapter considered PEC material, the optimization can be extended to antennas consisting of composite materials such as PEC and dielectrics.

Chapter Contents:

  • 5.1 Introduction
  • 5.2 Stored energies and fundamental bounds for antenna analysis and design
  • 5.2.1 Stored energies
  • 5.2.2 Qz' computation from current densities
  • 5.2.3 Fundamental bounds
  • 5.3 Antenna optimization
  • 5.3.1 Genetic algorithms
  • 5.3.2 Convex optimization
  • 5.4 Examples
  • 5.4.1 Bent-end simple phone model
  • 5.4.2 Bent-end simple phone model—optimization for Qz'
  • 5.4.3 Wireless terminal antenna placement using optimum currents
  • 5.5 Conclusions
  • References

Inspec keywords: Q-factor; antenna theory; genetic algorithms; method of moments

Other keywords: radiation pattern; antenna locations performance; small antennas optimization; SAR; efficiency limitations; antenna design; convex optimization problem; Q-factor; three-dimensional radiating structures; current distribution; embedded antennas; fundamental bounds; single-frequency estimation method

Subjects: Optimisation techniques; Other numerical methods; Antenna theory; Single antennas

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