Design Of Push-push Oscillator Based On Differential Band Pass Filter

The microwave signal sources are crucial components for the whole communication systems and they are designed as the local oscillators(LO)which could be widely applied to satellites,radars and wireless base stations.With the increased demand for the phase noise,the output frequency and the output power of the signal sources,more attention has been paid to the push-push oscillator.In this letter,the differential BPF with high Qsc factor and high CM suppression is utilized as a frequency stabilization element in designing the push-push oscillator which features low phase noise,high harmonic suppression and high output power.Firstly,the development and the theory of the push-push oscillator is introduced,then the working principle and the factors affecting phase noise of the oscillator could be clearly demonstrated which provide theoretical direction for the later design.Differential BPFs with high Qsc factor and high CM suppression have been designed based on the working principle of the differential filters.The differential SIW BPF is utilized as a frequency stabilization element in designing the push-push oscillator.The QSc-peak frequency of the BPF is chosen for the design at approximately half the output signal frequency to achieve low phase noise performance.A parallel feedback oscillator based on the complex quality factor has been proposed.Detailed design process of the oscillator is introduced which could be a theoretical reference for the design of the push-push oscillator.The first push-push oscillator with microstrip differential passband filter operating at X band has been proposed.The output frequency is 8.37 GHz with the phase noise of-134.6dBc/Hz(?)1MHz and the FOM of-197.03dBc/Hz.It has a lower FOM compared with other push-push oscillators.A differential substrate integrated waveguide filter is applied to the design of the push-push oscillator for higher oscillating frequency.The output frequency is 27.8 GHz with the phase noise of-128.6dBc/Hz(?)1MHz and the FOM of-201.5dBc/Hz(?)1MHz,and the phase noise performance has greatly improved compared with the first push-push oscillator.The expected performance of the proposed push-push oscillators have been achieved which indicates that the theoretical analysis is correct and the design approach is feasible.