There is disclosed a whispering gallery oscillator for producing a low noise microwave output signal. The whispering gallery oscillator comprises a dielectric resonator 1 comprising paramagnetic ions 34. A pump signal 5 is coupled by a coupler 7 to the paramagnetic ions to excite 19 the paramagnetic ions 34. The paramagnetic ions 34 decay 17 and thus excite a whispering gallery mode 15 of the dielectric resonator 1. The whispering gallery mode 15 is coupled by a coupler 10 to give an output signal 9. The whispering gallery mode 15 has a high Q (Q.apprxeq.10.sup.7) resonance. The high Q resonance results in a low-noise output signal 9. The paramagnetic ions 34 act as a MASER that is distributed about the dielectric resonator 1. In some embodiments, the whispering gallery oscillator may be locked to a frequency standard.