Microstrip to waveguide 3dB power splitter/combiner on FR4 PCB up to 50 GHz

A two microstrips-to-waveguide transition has been studied and tested for low-cost microwave circuit applications on FR4 multilayer boards, which have an internal thick metal plate. In order to improve the transmitted power, it's traditionally necessary to use a 3dB coupler and combine two MMIC devices. The implementation of the combiner on the substrate presents low performance due to the high loss factor of the material (i.e. tg/spl delta/FR4=0.025). To avoid this negative effect a novel circuit has been studied without any added insertion loss; the novelty of this approach is to sum the signal power inside the waveguide, in which two microstrip patch feeders, coming from the same side of the waveguide, are coupled through a slot. The slot works as transformer and it is implemented in the thick metal plate. The transition integration in the multilayer is obtained just screwing the board on the metal housing which includes the waveguide. Connecting properly the MMIC devices it's possible to improve the waveguide-side return loss or to obtain a push-pull configuration. Moreover, as the transition shows low sensitivity to manufacturing tolerances, the above process is characterized by high reliability and reproducibility.