Input resistances of small normal-mode helical antennas in dielectric materials

Recently, normal-mode helical antennas (NMHA) are expecting for radio wave sensor antennas used in a human body. Now, electrical characteristics of NMHA can be obtained through electromagnetic simulator calculations. However, for obtaining antenna performances conveniently, fundamental antenna parameters such as antenna input impedance, radiation resistance and ohmic loss resistance are better to be expressed by equation forms. In this paper, equations of these three types of resistances are deduced theoretically for antennas placed in dielectric materials. Effectiveness of equations is ensured through comparing equation results with electromagnetic simulation results.