Key Techniques Of High Performance Point Frequency Microwave Oscillator

The phase noise of oscillator affects not only the resolution capability of the receiving system but the error rate and carrier frequency’s tracking accuracy of the communication system. Therefore, the way to improve the performance of the system must reduce the phase noise of oscillator. Feedback oscillator is widely used in microwave circuits due to its simplicity of the structure and the feasibility of individual components. The feedback microwave oscillator studied in this paper is constructed by amplifier, resonator and phase shifter. The amplifier is used to meet the gain condition of the oscillation. And the resonator acts as a frequency selection device, analog phase shifter is added for the adjustments of the loop phase condition of the oscillation. Leeson’s phase noise model is adapted to investegate the phase noise performance of the oscillator, and this model shows that the performance of phase noise can enhanced by increasing Q value of the resonator or optimizing the frequency-locked loops, but the latter will add the complexity of the circuit with more fabrication costs. In this thesis a high-Q resonator is introduced to reduce the oscillator phase noise.This research includes the following parts:1. From the Leeson phase noise model, we analyzed the aspects which effect the phase noise of the oscillator, and finally get the relations between the oscillator phase noise and Q of resonator, the gain and the noise figure of the amplifier;2. From the composition of the feedback circuit, we designed the amplifiers, phase shifter and cylindrical cavity resonator. The amplifiers are low phase noise amplifier, which uses the HBT to replace the classical X band HEMT FET to reduce the amplifier phase noise. Resonant components are cylindrical cavity resonator, the manufacturing procedure of this resonator is very easy, and the resonator has a very high Q values, which could significantly reduce the phase noise of the oscillator. Phase shifter is a voltage-controlled reflection-type, and this type of phase shifters have a wide tuning range.3. We studied the problems in the tuning procession and the corresponding solution was proposed. Finally, we designed an X-band microwave point frequency oscillator with high-performance, and analyzed the oscillator on the experimental results.