Research On Push-push Type Injection-locked Substrate Integrated Waveguide Oscillator

As the modern communication technologies have been developed enormously,the higher frequency signals are required for transmitting the larger amount of information.However,the high frequency oscillators have a couple of practical problems,such as the phase noise,cost reduction,stability and output power.The push-push oscillator enhances the even mode harmonics and suppresses the odd mode output.The circuit doubles the fundamental frequency so that higher oscillating frequencies can be obtained.In this paper,a injection-locked pushpush oscillator that combines a push-push oscillator with a harmonic injection-locked oscillator is proposed,which can further optimize the phase noise performance of the push-push oscillator.This paper first starts with the theory of microwave oscillators.The parallel-feedback oscillators,push-push oscillators and injection-locked oscillators is analysed by introducing its circuit structure and phase noise model.The push-push structure introduced in this paper is different from the traditional double-push structure.A differential bandpass filter with high complex quality factor and high common mode rejection is used as its shared frequency selection network to ensure that the two sub-oscillators are completely symmetrical,which is beneficial to the optimization of phase noise.At the same time,the influence of complex quality factor on phase noise performance is also introduced in the phase noise analysis part.According to the above theoretical analysis,three types of oscillators are designed.All three oscillators are designed based on the theory of complex quality factor.Among them,the parallel-feedback oscillator and the push-push oscillator realize the function of a voltage-controlled oscillator.The oscillation frequencies of the three oscillators designed in this article all contain complex quality factor peak corresponding frequencies,and all have good phase noise performance:Firstly,a parallel-feedback type voltage-controlled oscillator is designed,using a resonator with a substrate integrated waveguide structure to ensure that the resonator has the best complex quality factor at the frequency index of 6.8GHz to obtain the best phase noise performance.At the same time,an adjustable phase shifter is added to the oscillation loop.The function of the voltage-controlled oscillator is realized by changing the phase of the loop.The output frequency range is 6.74-6.96 GHz,the tuning bandwidth is 220 MHz.The oscillator can tuned to the peak of the complex quality of the resonator.Secondly,in order to extend the oscillating frequency range,a push-push structure is adopted,and a differential filter with a complex quality factor peak at 6.8GHz is selected as the shared resonator.According to the differential output and differential output characteristics of the differential filter,directly The generation of two fundamental signals with opposite phases is more conducive to obtaining signals with low phase noise,high fundamental rejection and high second harmonic output power.Also,an adjustable phase shifter is added to the loop to realize the voltage-controlled oscillator Features.The final output frequency is 13.5-13.66 GHz,the tuning bandwidth is 160 MHz,the phase noise at 13.6GHz is about-132 d Bc/Hz@1MHz,and the corresponding FOM value is-198.65 d Bc.Finally,in order to further improve the phase noise performance,the harmonic injection locked oscillator is combined with the push-push oscillator,and the first oscillator is used as the injection source to generate two signals with opposite phases through the hybrid loop.It is injected into the two oscillation loops of the push-push oscillator to achieve injection locking,and the locking bandwidth is about 50 MHz.The frequency of the final output signal is 13.6GHz,the phase noise is about 137 d Bc/Hz@1MHz,and the corresponding FOM value is-203.65 d Bc.Consistent with the theory of injection-locked oscillators,it obtains better phase noise than the second oscillator.