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Output feedback control design techniques are required in practice due to the limited number of sensors/measurements available for feedback. This thesis focuses on output feedback controller design techniques for nonlinear systems subject to different system restrictions. The problem of controlling the heart dynamics in a real time manner is formulated as an adaptive learning output-tracking problem. For a class of nonlinear dynamic systems with unknown nonlinearities and non-affine control input , a Lyapunov-based technique is used to develop a control law. An adaptive learning algorithm is exploited that guarantees the stability of the closed-loop system and convergence of the output tracking error to an adjustable neighborhood of the origin. In addition, good approximation of the unknown nonlinearities is also achieved by incorporating a per- sistent exciting signal in the parameter update law. The effectiveness of the proposed method is demonstrated by an application to a cardiac conduction system modelled by two coupled driven oscillators. An output feedback design technique is developed to achieve semi-global practical stabilization for a class of non-minimum phase nonlinear systems, subject to param- eter uncertainties. This work provides a constructive controller design method for an auxiliary system, whose existence is crucial, but is only assumed in (Isidori, 2000). The control design technique is used to regulate the benchmark van de Vusse reactor. Simulation results demonstrate satisfactory controller performance. The output feedback control design for a class of non-minimum phase nonlinear systems with unknown nonlinearities is studied. The proposed approach is able to combine the two previous design methods and provide a stabilizing output feedback control law. The performance of the proposed method is demonstrated by simulation results. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2009-12-22 15:47:05.884

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In this thesis, the concept of multi-phase centre virtual antenna is thoroughly investigated when a dual-mode primary feed is placed at the focal point of an offset reflector antenna. The virtual antenna requires that the antenna have multiple phase centre locations with identical radiation patterns. It is shown that different polarizations and mode content factors of a dual-mode circular waveguide can displace the phase centre location of an offset reflector antenna without changing its radiation patterns in any direction. This novel idea has promising applications in modern satellite, remote sensing, global positioning systems, and radars with moving platform. The concept is well matched for the modern Displaced Phase Centre Antenna technique, in which a simple signal processing technique is employed to electronically displace the phase centre locations. To avoid mechanically rotating the primary feed, a novel dual-mode feed is also proposed and implemented. It is capable of generating two perpendicular polarized TE11 modes with a fixed aligned TE21 mode. The antenna such developed has a potential application as a transceiver in ground moving target indicator radars. All numerical results are successfully validated by fabricating and testing a prototype antenna in practice. As known, an offset reflector fed by a conventional linear polarized feed suffers from high cross polarization level. This property is also investigated for single-phase centre antenna applications along with sidelobe level and aperture efficiencies. A simplified feed model is proposed utilizing the TE11 and TE21 type modes to reduce the cross polarization at both asymmetry and inter-cardinal planes. It is shown that an asymmetric dominant TE11 mode with the presence of the TE21 mode is sufficient in order to reduce the unwanted cross polarization. The results of this investigation are used to design practical dual-mode feeds using simple circular waveguide geometries. To complete the study, the effects of linear and quadratic phase errors associated with the optimized primary feed are also investigated on the cross polarization of the offset reflector antennas. In particular, the phase errors resulting in separate phase centre locations of each mode produce broadside-shape cross polarized patterns instead of boresight-null ones.

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