Abstract: A microwave microstrip/slotline frequency-halving circuit configuration is disclosed in which the frequency division is based on the principle of parametric subharmonic generation. The circuit comprises a subharmonic resonator formed partially by the overlap of an open-circuited microstrip line on one side of a dielectric substrate and a short-circuited slotline in the ground-plane on the other side of the substrate. The resonator is completed by a pair of varactor diodes symmetrically placed in holes in the dielectric substrate so as to form connections between the end of the microstrip line and the two sides of the slotline below. An input signal at frequency 2f entering via the microstrip line results in the propagation of a signal at frequency f in the output slotline.