Electrically small loop surrounded by a “shell” of concentric split rings: Principle and properties

The paper describes a novel electrically small antenna structure and investigates its physical principle and properties. The antenna is formed by small planar loop with a “shell” of three concentric split rings with external electrical dimension ka=0.4. The structure has been designed with complex impedance Z_in ~22 + j195 Ω to be utilized as UHF RFID tag antenna. The physical principle is explained via the simulated surface current distribution and several parametrical studies.