Microstrip disk antennas, Part I: Efficiency of space wave launching

A theoretical study on the problem of surface wave excitation of microstrip disk antennas is presented. The cavity model with magnetic sidewalls and dyadic Green\´s functions in stratified media is used to obtain the radiated fields in an integral form. Lossless media are assumed such that there is no cross coupling between the powers in the space ( ) and surface ( ) waves. The separate contributions of these two powers is examined. With the assumption that does not contribute to the main radiation patterns of the antenna an efficiency of space wave launching and a corresponding antenna directivity are defined. Values of efficiency and directivity as functions of the dimensions of the antenna and for two values of dielectric constants of the substrate are shown. Agreement of these results with some of the available data is observed. It is worth noting that may correspond to an appreciable portion of the total radiated power.