Development of a low phase noise microwave voltage controlled oscillator
Date
2008-12
Authors
Vermaak, Elrien
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
The topic for this project entailed the development of a ‘Low Phase Noise –
Microwave – Voltage Controlled Oscillator’ for use in radar applications.
First of all, a low phase noise oscillator was designed. In order to minimise
the phase noise of the oscillator, a high-Q, transmission line – cavity resonator was
developed. By derivation it was confirmed that an optimal point for minimum phase
noise does exist. The latter was done by evaluating the equation for the output
power spectral density of the oscillator phase noise (as defined by Leeson’s Phase
Noise Model) at its minimum point. Subsequently, the amount of power that needed
to be dissipated inside the resonator could be compared to that dissipated in the
source and the load. This identified the amount of coupling to the resonator allowed,
assuring minimum phase noise. Since a specific amount of coupling to the resonator
was sought after, it had to be practically feasible. Therefore several coupling
techniques were investigated to ensure the most user-friendly way of tuning the
amount of coupling to the resonator, and hence easily reaching the optimum point of
minimum phase noise.
After successful completion of the low phase noise oscillator design, it was
modified for voltage controlled oscillator (VCO) use by means of variable tuning
diodes. These varactor diodes were situated inside the cavity of the resonator.
Again the most suitable position to place the diodes had to be determined. The latter
was done through considerably detailed transmission line theory; where the loaded
Q, the tuning bandwidth (amount of change in frequency reached) and the amount of
power dissipated inside the resonator were measured against each other.
By means of the necessary phase noise measurements, it was confirmed
that in order to keep the phase noise to a minimum, the tuning bandwidth had to be
kept small and the amount of power dissipated inside the resonator maximised; so as
to keep the overall loaded Q-value of the circuit as high as possible.
Description
Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008.
Keywords
Cavity resonator, Microwave, Phase noise, Theses -- Electronic engineering, Dissertations -- Electronic engineering