Abstract: A transition structure between a transmission line of a multilayer PCB and a waveguide is proposed. The transition structure includes the waveguide comprising an interior space on one side thereof and having an inlet for accommodating a part of a stripline, the transmission line comprising a first ground layer of the multilayer PCB composed of at least two or more dielectric layers, the stripline extending from the transmission line and protruding into the waveguide through the inlet of the waveguide, and a single via hole or a plurality of via holes formed between the first ground layer and a bottommost ground layer, wherein each via hole is positioned at the inlet of the waveguide.