Stripline to microstrip line aperture coupler

Aperture coupling between stripline and microstrip line is analyzed as a function of the electric and magnetic polarizabilities of the aperture, using Bethe´s small-aperture coupling theory. A coupling expression for the general case of an aperture in the common ground plane is derived. Coupling variations with aperture dimensions for the case of a thin slot, a hole, a diamond, a rounded end slot, and an ellipse are determined using McDonald´s polynomial approximations for the electric and magnetic polarizability for small apertures. Experimental results for the case of a thin slot and a circuit aperture are also presented