Abstract: A transition between a waveguide and transmission line is disclosed in which a probe portion of the transmission line extends into the waveguide to electrically field couple signals between the waveguide and transmission line. The transmission line is preferably a coplanar fuse and includes a substrate having conductors disposed therein which prevent energy from propagating into the substrate from the waveguide. Propagation of energy into the desired transmission line mode is therefore facilitated. Because the probe is formed as an integral part of the transmission line, direct coupling to the waveguide is possible without the use of intervening sections, transitions or transmission lines. The transition may be scaled in order to couple a wide range of frequencies.