A conducting plane resonator (10) is used to stabilize an oscillating means (12) typically operating at microwave frequencies. The conducting plane resonator (10) is in proximity to the oscillating means (12) and is magnetically coupled thereto. In a first implementation, the conducting plane resonator (10) is magnetically coupled to an input conductor (16) of the oscillating means (12). In a second implementation, the conducting plane resonator (10) is magnetically coupled to an output conductor (18), which is coupled to the oscillating means (12). In a third implementation, the conducting plane resonator (10) is magnetically coupled to both the input conductor (16) and the output conductor (18). The conducting plane resonator (10) preferably comprises a thin, substantially planar conducting plane and is dimensioned such that it is resonant at the desired operating frequency. The conducting plane resonator (10) is preferably fabricated of a superconductor material to achieve high-Q performance.