This paper presents a theoretical model of a cylindrical ferrite resonator (FR) antenna that predicts resonance frequencies, the frequency tuning range, and radiation patterns. The FR antenna is placed on a PEC ground plane and is excited by a coaxial probe with a dc magnetic bias field applied in the direction transverse to the ground plane. An open-boundary model to predict the resonance frequency is introduced and compared with the measured results. The all-boundary model is in good agreement with the measured results compared with the other models. The discrepancy of the proposed model is less than 3%. The HE11 delta mode-splitting behavior caused by the tensor nature of the permeability of a biased ferrite is investigated. It is shown that the frequency and polarization of the antenna are tunable. The operating frequency can be chosen in the range from 8.54 to 10.115 GHz. In addition, the linear polarization is radiated at no bias, while the circular polarization is radiated at the magnetized case. The results of the theory correspond approximately with the measured and simulated results for radiation patterns.