A push-push microwave oscillator has two branch oscillators fabricated of a transistor and transmission line elements extending from terminals of the transistor, and a resonator which is fabricated of an annulus of superconductor material and serves to phase lock oscillations of the two branch oscillators. The superconductor material is a composite of a rare earth element and copper oxide such as yttrium-barium-copper oxide. A first transmission line in each of the branch oscillators extends past the resonator with a spacing to provide for electromagnetic coupling between the branch oscillator and the resonator. A second transmission line in each of the branch oscillators has a length equal to approximately one-quarter wavelength of the oscillation frequency to tune the branch oscillator to a common oscillation frequency. A third transmission line in each of the branch oscillators extends towards a junction point to form a summing unit for summing oscillations of the two branch oscillators to provide an output signal of the oscillator. The oscillator is constructed in stripline or microstrip form wherein components of the branch oscillators are coplanar with the resonator and are spaced apart from a ground plane by a dielectric layer of alumina or lanthanum aluminate. Power is extracted at an even multiple of the fundamental frequency, and has a improved accuracy of frequency and reduced phase noise, the latter arising because of a characteristic of the superconductor material wherein its microwave surface resistance increase proportionally with a square of an increase in frequency.