Abstract:
Transistor oscillators with planar micro strip resonators as frequency determining
elements are widely used as stable sources for microwave systems because of their easier
implementation and lower cost. This thesis is concerned with the development of oscillators
using different micro strip resonators. Two negative resistance oscillators are designed and
implemented. First oscillator is designed using λg/2 resonator. Short circuited stubs at source are
used for the purpose of device instability. Short circuited stubs also induce instability at other
undesired frequencies which causes wideband oscillations. The problem of wideband instability
is solved by removing the short circuited stubs at source and directly grounding the device.
Oscillator has measured output power of 4 dbm at carrier frequency of 3.72 GHz with phase
noise of -40dBc/Hz at offset of 100 KHz. In this case, resonator is over coupled, in order to
select optimum terminating impedance point in unstable region of device, which causes
reduction of Quality factor of resonator.
Second oscillator is designed using circular ring resonator. Device is directly grounded and
over coupled circular ring resonator is used. Resonator is over coupled in order to select
optimum terminating impedance in unstable region of device. This circuit has measured output
power of 1.1dBm at carrier frequency of 3.89 GHz with phase noise of -45dBc/Hz at offset of
100 KHz. A comparison of general characteristics of above mentioned oscillators will be
presented in this work.
