A theoretical model of a cylindrical ferrite resonator antenna with a dc magnetic bias, applied in the direction parallel to the antenna height, is proposed. HE11 delta mode splitting behavior caused by tensor nature of the permeability of a biased ferrite is investigated. The proposed model is validated through an experimental investigation of the HE11 delta mode antenna. This communication utilizes a Li-ferrite suitable for the antenna applications. The presented theory is shown to correlate well with the measured results. It is also found that HE11 delta mode splitting behavior of the antenna involves frequency and polarization, and bandwidth tuning performances. Therefore, the antenna is a good candidate for a multifunctional antenna.