Spherical and spheroidal antennas in resonant, quasi-resonant and antiresonant shells with negative permittivity

According to simulated results obtained by the method of eigenfunctions, the performance of electrically small spheroidal antennas in shells with negative permittivity depends on a combination of resonant and antiresonant properties of the antennas. According to the quasi-static model presented in this study, resonant and antiresonant properties of the antennas are functions of permittivity of the shells, shapes and electrical sizes of the antennas. Comparison of the obtained relations with Mie theory and the Rayleigh model shows similarity of antiresonance of the antennas with surface plasmon resonance of sub-wavelength scatterers. The shell size, radiation resistance, power and efficiency of radiation of prolate spheroidal antennas in confocal shells are comparatively fast functions of permittivity in antiresonant ranges. More gradual emergence of antiresonant properties of the oblate spheroidal and spherical antennas makes them more suitable for combining optimal values of performance parameters. The quality factor of the antennas tuned to zero reactance is proportional to (|ε|1)|ε|. As a result, it is closer to the Chu limit in antiresonant ranges as compared to the resonant ranges.