A low noise PLL-based frequency synthesiser for X-band radar
Date
2008-03
Authors
Moes, Henderikus Jan
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
This thesis discusses the design, development and measured results of a phase-locked loop based
frequency synthesiser for X-band Doppler radar. The objective is to obtain phase noise comparable
or lower than that typically achieved with direct analogue frequency synthesis techniques. To meet
this objective, a theoretical study of the noise contributions of individual components of the synthesiser
and their effect on the total phase noise within and outside the loop bandwidth of the PLL is
performed. The effect of different phase margins on the closed-loop frequency response of the PLL,
and hence the total phase noise, is investigated. Based on the results, an optimal phase-frequency
detector reference frequency, loop bandwidth, adequate phase margin, and suitable components are
chosen for optimal phase noise performance. The total phase noise at the output of the synthesiser is
calculated and it is shown that the phase noise specification can be met.
A significant part of this thesis is devoted to the design, modelling and characterisation of a frequency
multiplier, as well as to a combline and interdigital bandpass filter required for the frequency
synthesiser. In the first case, a piecewise linear circuit model is used to model the behaviour of the
nonlinear multiplier circuit. Fourier theory is used to calculate the large-signal driving point input
and output impedances of the nonlinear circuit, enabling the computation of the circuit elements for
the input and output matching networks. The measured response of the frequency multiplier under
various different operating conditions is presented and discussed. The design of the microwave
bandpass filters is based on the theory of coupling and external quality factors. To aid in the verification
and optimisation of the design, a software simulation tool is used. The presented S-parameter
measurements of the filters show how well the theory matches with what is obtained in practice.
The measured spectral and phase noise response of various components comprising the synthesiser,
are discussed. These measurements provide insight into the response of individual components
under different operating conditions and show the behaviour of important subsystems of the synthesiser.
The thesis culminates in the presentation of the measured phase noise of the complete synthesiser.
It is shown how well the measured phase noise correlates with the calculated phase noise.
In addition, the measured spectral content and transient behaviour of the synthesiser are investigated
and discussed. High power spurious components at some output frequencies are indentified
and reduced. The feasibility of using the developed prototype phase-locked loop based frequency
synthesiser for coherent X-band Doppler radar is discussed and demonstrated.
Description
Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008.
Keywords
Theses -- Electrical and electronic engineering, Dissertations -- Electrical and electronic engineering