Design of a miniaturized stripline-to-microstrip-line coupler

A new design methodology for a stripline-to-microstrip-line coupler using apertures in their common ground plane is presented. The design is based on a cosine distribution of aperture sizes and allows the component to be realized within one fifth of a wavelength while maintaining a broadband performance. Various key points of the design such as aperture dimensions and the number of apertures are discussed. The theory is validated by measurements.