Low Phase Noise Concurrent Dual-Band Oscillator Using Compact Diplexer

A novel C-band concurrent dual-band oscillator is presented in this paper. Two diplexers are cascaded back-to-back to realize two loop sub-oscillators. The phase noise of the oscillator is reduced significantly by using the cascaded high-Q diplexers as the frequency stabilization elements. Meanwhile, a highly pure dual-band signal was observed at the output port, which is contributed to the isolation characteristic of the diplexers. The diplexers can suppress the interaction between the two sub-oscillators. To obtain the property of compact size and high-Q factor, the SIW-CSRR structure is introduced into the design of diplexers. A C-band prototype has been designed and fabricated. The measured phase noise of the dual-band oscillator is -112.3 dBc/Hz and -110.3 dBc/Hz at 100 kHz offset from 4.18 and 5.49 GHz oscillation frequencies, which correspond to the figure-of-merit (FOM) of 188.7 and 189.1 dBc/Hz, respectively. The second-order and third-order intermodulation products of the two oscillation signals are suppressed to below -24 dBc, as compared to the 4.18 GHz signal.