Low phase noise cylindrical cavity oscillator

[摘要] ENGLISH ABSTRACT: The objective of this thesis is to develop a 9.2 GHz low phase noise oscillator with a cylindrical cavity resonator.A cylindrical metal cavity with air as dielectric was used as a resonator. To minimise the phase noise of the oscillator, the resonator must be designed to have a high Q-factor. A high Q-factor was obtained by designing the resonator to operate in the TE011 mode. A tuning screw was used to tune the resonant frequency without significantly affecting the Q-factor. The tuning screw also separates the resonant frequencies of the degenerate TE011 and TM111 modes. The signal is coupled to the resonator by means of rectangular apertures. The coupling was designed to minimise the phase noise of the oscillator.A dual mode waveguide filter was developed and inserted into the oscillator loop in order to prevent oscillation at unwanted frequencies.Due to the excellent phase noise performance of the oscillator, it was not possible to measure the phase noise directly with the available phase noise meter. A measurement setup using two similar oscillators tuned to oscillate at frequencies differing by about 60 MHz was implemented. The output signals were down-converted to the difference frequency where the phase noise could be measured accurately.The output signal of the oscillator was measured at different locations in the loop and clearly showed that the resonator can be used as a filter to minimise the phase noise.The performance of the oscillators met all expectations. Phase noise levels of -115 dBc/Hz and -146 dBc/Hz were obtained at offset frequencies of 10 and 100 kHz.

[发布机构] Stellenbosch University