A study of a monopole arbitrarily located on a disk using hybrid MM/GTD techniques

The input impedance of a monopole located off-axis on a disk and oriented in an arbitrary direction is investigated using hybrid method of moments/geometrical theory of diffraction (MM/GTD) techniques. The equivalent currents method (ECM) and the uniform geometrical theory of diffraction (UTD) are used to ensure a proper treatment of each situation. A criterion for switching from UTD to ECM in the vicinity of the axial caustic is discussed. Measurements of impedance have been made in order to check the numerical results and are presented here, showing good agreement with theory.