PHASE NOISE PERFORMANCE EVALUATION OF OSCILLATORS USING VARIOUS RESONANT CIRCUITS.pdf

Abstract

Microwave oscillator is a crucial part of all microwave systems such as radars, communication systems, as well as navigation and electronic warfare systems. The noise produced by oscillator is critically important in practice because it may severely degrade the performance of the system. A noisy local oscillator leads to down conversion of undesired nearby signal, thus limiting the selectivity of the receiver. The phase noise also introduces uncertainty during the detection of digitally modulated signals, especially in the case of PSK or QAM modulation. In this thesis phase noise performance of three oscillators using different types of resonators; Dielectric Resonator (DR), Planar Microstrip and Defected Ground Structure (DGS) resonators have been evaluated. Agilent’s Advance Design System 2008 and AWR’s Microwave Office are used in the designing of these oscillators. Small signal S‐parameters as well as large signal models were used to predict oscillation frequency, output power, harmonic contents and phase noise. The three demonstrated oscillators have the same basic common source configuration and series feedback topology. Our frequency of interest was 2.60GHz, however due to unavailability of material the DR based Oscillator was designed at 2.7GHz. This difference in frequency has negligible effect on phase noise performance of oscillator (according to Lesson’s formula) [8]. The phase noise performance mostly depends on loaded Q‐ factor of the resonators. The DR based oscillator shows an output power of 4.5dBm and the measured phase noise is ‐91.60dBc/Hz, ‐107.89 dBc/Hz and ‐126.25dBc/Hz at 10KHz, 100 kHz and 1 MHz offset frequencies respectively. The planer microstrip resonator based oscillator was designed at 2.60 GHz. The measured phase noise was ‐63.95dBc/Hz, ‐85.94dBc/Hz and ‐115.66 dBc/Hz at offset frequencies of 10 KHz, 100 KHz and 1 MHz respectively. The most promising technique to realize a low phase noise oscillator is to imply a High Quality Resonator such as dielectric Resonator. However, it can’t be used in microwave monolithic integrated circuits (MMIC) on chip due to its non‐planar structure. In recent years, there have been new technologies to design oscillator for planar structures. iii Unfortunately, the phase noise of planar structures is not as good as the dielectric resonator oscillators; because of the low quality factor of the planar resonators at lower measuring phase noise offset frequencies. A new technique to improve the Quality factor of the resonator in microwave oscillator is used by implementing a spiral shaped defected ground structure (DGS) resonator. By using DGS resonator we achieved loaded quality factor of 520, which was 21 in case of planer microstrip resonator at 2.60GHz. The measured phase noise is ‐80.74dBc/Hz, ‐94.91dBc/Hz and ‐122.80dBc/Hz at 10 KHz, 100KHz and 1MHz offset frequencies respectively