Research On Novel Low Phase Noise Microwave Oscillators

With the rapid development of wireless communication technology,microwave devices are used more and more frequently.To provide local signals,microwave oscillators play an important role in various communication systems.Oscillation frequency,phase noise,output power and harmonic suppression are the important performance indexes of a microwave oscillator.Among them,phase noise is the most important one.Therefore,this dissertation focuses on exploring the microwave oscillators with low phase noise from the aspects of theoretical principle,topology and design method.The main work includes the following aspects:1.Two novel parallel feedback single-ended oscillators are proposed.Firstly,a filter based on E-type dual-mode step impedance is proposed.A transmission zero is introduced next to the passband to increase the group delay.The measurement results show that the oscillator based on the designed filter works at 3.52 GHz.A low phase noise-122.23 d Bc/Hz is obtained at offset 100 k Hz and the output power is 2.21 d Bm.Secondly,a compact filter based on combline resonators and one incurvate ring resonator is proposed.It generates three transmission zeros that can be shifted flexibly.Based on this filter,the oscillator operating at 2.01 GHz is designed.The measured phase noise is-128.59 d Bc/Hz at offset 100 k Hz,which is the lowest phase noise among S-band oscillators reported publicly in domestic and overseas.Meanwhile,the high output power of 8.32 d Bm is realized.Compared with similar devices,the oscillator has superior performance.2.A novel concurrent dual-frequency oscillator is proposed.The two sub-oscillation loops are connected by a four-port diplexer and a three-port diplexer.And the output power of the oscillator is improved by cascading low noise amplifiers(LNAs)for the first time.For verification,an oscillator example with the center frequencies of 2.01 and 3.51 GHz was designed and fabricated.The phase noises are-118.97 and-122.67 d Bc/Hz at offset 100 k Hz,respectively.The harmonic suppression is better than 51.45 d B in the full frequency band tested.The dual-frequency oscillator shows superior phase noise and harmonic suppression performance.3.A high-performance voltage-controlled oscillator(VCO)is proposed.An electromagnetic mixed coupling tunable filter with constant absolute bandwidth in the tuning range is proposed and applied to the design of the VCO.The measured results show that the tuning range is 1.745-2.284 GHz,about 26.76%.In the whole tuning range,the phase noise varies from-113.61 to-118.71 d Bc/Hz at offset 100 k Hz,and the second harmonic suppression reaches 48.7 d B.Compared with other similar works,the proposed VCO achieves low phase noise performance,a wider tuning range and outstanding harmonic suppression ability.