Evolutional Design of Small Antennas for Passive UHF-Band RFID

This paper presents evolutional design of antennas for UHF-band passive IC tags. The wire-antenna shapes are optimized using the genetic algorithm (GA) aiming at maximization of feeding power to the IC tag as well as minimization of the antenna size. The characteristics of the antennas printed on a dielectric substrate are evaluated using the moment method in the optimization processes. The genotypes for GA are introduced to express the shapes of lattice antennas, which include loops and floating lines, and spiral antennas. The present genotypes for the latter are also valid for optimization of spiral structure of, for example, inductors and filters. It is shown that optimized lattice and spiral antennas have smaller sizes in comparison with the conventional meander antennas.