Research On Low Phase Noise Microwave Oscillators Based On Novel Planar Frequency Selection Structures

In recent years,with the rapid development of wireless applications such as personal mobile communications and military equipment,the microwave and wireless markets have received much attention.Microwave oscillators are an integral part of the frequency source and their performance can affect the performance of the entire wireless communication system.The oscillator's oscillation frequency,output power,and phase noise are important factors in the overall system design.In this thesis,an in-depth study on the construction of low phase noise microwave oscillator is carried out,focusing on the topology,theoretical principle and design method of the new frequency selective structure,and its application in the construction of low phase noise microwave oscillator.The main work includes the following aspects:1.Two novel microstrip bandpass filters with quasi-elliptic frequency response are proposed.Using lumped parameter equivalent circuits to clearly reveal their physical mechanisms provides a reliable design method and shortens design time.The constructed filter has transmission zeros on both sides of the passband,significantly improving frequency selectivity and out-of-band performance.The relative bandwidths of the two filters tested were 36%and 38.5%,respectively,and the out-of-band rejection was 42dB and 32dB,respectively,and the return loss was greater than 15dB.Compared with similar microstrip filter structures at home and abroad,the microstrip filter proposed in this thesis has significant advantages in performance and size.2.An elliptical narrowband bandpass filter based on step impedance resonator(SIR)is proposed and a low phase noise microwave oscillator is constructed.The filter has a transmission zero on each side of the passband and a high rejection of more than 30dB at the second/third harmonic.In addition,a group delay response greater than 9.6 ns can be obtained over the passband frequency range.A microwave oscillator based on this filter is designed.The phase noise test results of the oscillators in this thesis are the same as the best reported in domestic and foreign literature,and the harmonic suppression performance is better than them.3.A novel SIW narrowband elliptical filter is proposed and a low phase noise microwave oscillator is constructed.The filter is based on the parallel branches of the SIW circular resonator and can generate two transmission zeros,achieving a steep transition band with an out-of-band rejection greater than 48 dB.By adjusting the bandwidth,a group delay region greater than 10 ns is implemented in the passband.This filter was applied to an X-band oscillator,and the second harmonic suppression of 60.3dBc was obtained,and a low phase noise of-120.06 dBc/Hz was obtained at offset 100KHz.The phase noise test results of the oscillators in this thesis are close to the best level reported in domestic and foreign literature.4.A narrow-band Chebyshev filter based on a suspended microstrip cavity is proposed and applied to a low phase noise microwave oscillator.Since the air cavity of the suspended microstrip has a high Q_L value,the filter has a group delay region greater than 11 ns in the band and a 40 dB high rejection at an offset center frequency of 300MHz.Using this filter as the frequency selective structure of the X-band oscillator,a low phase noise of-120.86 dBc/Hz is obtained at offset 100 KHz while achieving 51.5dBc second harmonic suppression.