A Novel Low Phase Noise Oscillator Using Stubs Loaded Nested Split-Ring Resonator

In this letter, a novel low phase noise oscillator based on stubs loaded nested split-ring resonator (SLNSRR) is proposed. The SLNSRR consists of a nested split-ring resonator (NSRR) and two short-circuited stubs loaded symmetrically at the NSRR bottom. It possesses a compact size about <inline-formula> <tex-math notation="LaTeX">$0.094\,\,\lambda _{g} \times 0.129\,\,\lambda _{g}$ </tex-math></inline-formula> (where <inline-formula> <tex-math notation="LaTeX">$\lambda _{g}$ </tex-math></inline-formula> is the guided wavelength at the center frequency). Based on the proposed SLNSRR, a close-to-upper passband transmission zero has been realized in a bandpass filter. The filter has a sharp phase variation and leads to a steep group delay, which can obtain better phase noise performance in an oscillation circuit. For verifying the design, an L-band oscillator has been fabricated and measured. The measured results show that at the oscillation frequency of 1.98 GHz with 9.5-dBm output power, the phase noise is −127.22 and −145.43 dBc/Hz at 100-kHz and 1-MHz frequency offset, respectively. The figure-of-merit at 100-kHz frequency offset is −198.4 dBc/Hz.