Analysis and design of profiled multiaperture stripline-to-microstrip couplers

A new design methodology for a stripline-to-microstrip coupler is presented. Using circular apertures in their common ground plane, it is demonstrated that a design based on profiled circular apertures can be realised within a fraction of a wavelength while maintaining a comparable broadband behaviour. Various key points of the design, such as aperture dimensions and the number of apertures, are discussed. The analysis is based on weak coupling, and includes the mutual interactions of apertures. The theory is validated by measurements of prototypes with a constant, a sine and a cosine profile of apertures.