A novel ellipsoidal helical antenna is proposed and studied in this letter. As a special in-stance,the hemispherical helical antennas are analyzed firstly,which indicates that the characteristics of a two-arm unit are better than that of a single-arm unit. Based on this,the ellipsoidal helical antenna,formed by changing the axial direction’s dimension of the two-arm hemispherical helical antenna,is analyzed by the moment method with curved basic and testing function. The effects to VSWR (Voltage Standing Wave Ratio),gain,polarization and patterns by the axial direction’s dimensions are inves-tigated. The study results provide dependable gist to the choice of antenna format according to the practical requirements. A novel ellipsoidal helical antenna is proposed and studied in this letter. As a special in-stance, the hemispherical helical antennas are analyzed first, which indicates that the characteristics of a two-arm unit are better than that of a single-arm unit. Based on this, the ellipsoidal helical antenna, formed by changing the axial direction’s dimension of the two-arm hemispherical helical antenna, is analyzed by the moment method with curved basic and testing function. The effects to VSWR (Voltage Standing Wave Ratio), gain , polarization and patterns by the axial direction’s dimensions are inves-tigated. The study results provide dependable gist to the choice of antenna format according to the practical requirements.