A broadband microstrip to waveguide transition for FR4 multilayer PCBs up to 50 GHz.

A broadband microstrip-to-waveguide transition has been studied and tested for low-cost microwave circuits on FR4 multilayer boards having an internal thick metal plate (1). It is obtained, at first, milling a slot in a thick metal plate. Subsequently the PCB is built up, using standard PCB process, inserting the thick metal plate as the second layer. In this way the slot results filled with FR4 prepreg. A further simple milling process removes the lower layers up to the thick metal plate and creates a part of the waveguide transformer and an area for plate to metal housing connection. The transition integration in the multilayer is obtained just fixing the board on the metal housing which includes the rest of the transformer and the waveguide. Moreover, as the transition shows low sensitivity to manufacturing tolerances, the above process is characterised by high reliability and reproducibility.