Superconducting balanced mixer

A doubly-balanced mixing circuit for RF signal detection, having an RF input, a local oscillator input and an IF output, comprising a current controlled switching network in the form of a superconducting film and current source means for applying a DC bias current to the superconducting film for biasing the film to a quadratic region of its operating characteristic, the film being in the form of an annulus having a generally radially disposed gap therein, the current source means being connected across the gap, the RF signal being input to the film through transformer means, the primary of the transformer means being connected to an RF source and the secondary of the transformer means being connected across the annulus between a first location approximately adjacent the gap and a second location approximately diametrically opposite the first location, the gap being substantially a short circuit to the RF signal and an open circuit to the DC bias current, and the local oscillator input being connected across the annulus at diametrically opposite locations rotated approximately 90 degrees from the RF input locations, the IF output being taken from the center of the secondary of the transformer means.