- A theoretical model to analyze the performance of a circular polarization microstrip antenna printed on a conical surface is presented. The radiation pattern of the antenna is simulated by the radiation from its four radiating edges (two axial and two circumferential). The electromagnetic field is expanded in terms of spherical wave modes and it is shown that the circular polarization is obtained by exciting in the antenna two spherical TE/sub r/ orthogonal modes with 90/spl deg/ phase difference. The impedance analysis is based on the cavity model. Experimental data fits well the theoretical predictions of the model.