Substrate effect on X-band design of end-wall double slit microstrip-to-waveguide splitter

End-wall waveguide-to-microstrip splitters are highly favourable to feed series´ fed microstrip arrays. The presented topology of a double slot microstrip transition clearly shows distinct advantages. To investigate the effect of substrate material and thickness on this kind of transition three different substrates are used for the transition design. Simulation and measurement results are compared. Finally, one of the designs is applied to feed an antenna array.