Abstract: A mixer circuit in which a high frequency signal and a local oscillation signal are applied to two ports respectively of a rat-race having four ports, and the other two ports are connected at one end thereof to grounded diodes respectively. An intermediate frequency signal is derived from a filter connected to a circular loop in the rat-race. The distances of the two arcuate transmission paths between the connection point of the filter and the diodes are selected to be equal to each other, and the two arcuate transmission paths between the connection point of the filter and the high frequency signal input port are selected to have a distance difference corresponding to one half the wavelength of the high frequency signal.

Abstract: A mixer circuit using a rat-race constituted by disposing microstrip lines on one surface of a substrate to provide a loop-shaped transmission line and four transmission lines connected to the loop. In the rat-race, two of the four transmission lines are disposed within the loop of the loop-shaped transmission line. A conductor penetrates the substrate at the center of the loop of the loop-shaped transmission line, and a pair of diodes are connected respectively between this conductor and the two transmission lines disposed within the loop so that an intermediate frequency signal obtained by subjecting a high frequency signal to frequency conversion can be derived from the conductor at the other surface side of the substrate.