Design of low phase-noise microwave oscillators using two-pole coupled-resonator filters with electric, magnetic, and mixed couplings

In this paper, three filter-based microwave oscillators are developed using two-pole coupled-resonator filters with the electric, magnetic, and mixed coupling structures. The filter embedded in the feedback network plays an important role to improve the stability and selectivity performances of the oscillator. Besides, considering the effects of the insertion loss of the filter, the complex quality factor Q_SC is adopted for the oscillator design. The developed oscillator with the electric coupling filter is experimentally demonstrated at 2.0065 GHz with -140 dBc/Hz phase noise at 1 MHz offset frequency. On the other hand, the oscillators using the magnetic-and mixed- coupling filters operated at 1.987 GHz and 1.996 GHz have measured phase noises of -139.6 dBc/Hz and -136.81 dBc/Hz at 1 MHz offset frequency, respectively.