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Climate change and continuously increasing energy prices have driven the need for low carbon and renewable energy technologies from different sectors, including the domestic sector, by installing higher energy efficiency technologies. One of these technologies is the Stirling engine based micro-combined heat and power (CHP) which has the potential to achieve lower overall carbon emissions by generating both heat and electricity locally. Its successful implementation to meet the energy demands (thermal and electrical) throughout the year depends on several factors such as the size and type of building and demand profiles. In addition, the deployment of large number of micro-CHPs may have significant impact on the performance of the power distribution networks.

In response to the high demand of the operation reliability by implementing real-time monitoring and system health management, the three-year PhD project focuses on developing robust fault diagnosis and fault tolerant control strategies for complex systems with high-nonlinearities, stochastic Brownian perturbations, and partially decoupled unknown inputs, which are then applied to wind turbine energy systems. Integration of serval advanced approaches, including the augmented system method, unknown input observer design, Takagi-Sugeno fuzzy logic, linear matrix inequality optimization, and signal compensation techniques enable us to achieve robust estimations of both the system states and the faults concerned simultaneously, while removing/reducing the adverse influences from faults to the system dynamics. Prior to the existing work, the considered unknown inputs can be partially decoupled rather than completely decoupled, which can meet a wider practical requirement. Moreover, the systems under investigation can be linear, Lipschitz nonlinear, quadratic inner-bounded nonlinear, high-nonlinear characterized by a Takagi-Sugeno fuzzy model, and stochastic with Brownian perturbations, which can cover a wide range of real industrial plants. Specifically, the augmented system method is used to construct an augmented plant with the concerned faults and system states being the augmented states. Unknown input observer technique is thus utilized to estimate the augmented states and decouple unknown inputs that can be decoupled. Linear matrix inequality approach is further addressed to ensure the stability of the estimation error dynamics and attenuate the influences from the unknown inputs that cannot be decoupled. As a result, the robust estimates of the faults concerned and system states can be obtained simultaneously. Based on the fault estimates, a signal compensation scheme is developed to remove/offset the effects of the faults to the system dynamics and outputs, leading to a stable dynamic satisfying the expected performance. A case study on a 4.8 MW wind turbine benchmark system is proposed to illustrate and demonstrate the proposed integrated fault tolerant control techniques. Takagi-Sugeno modelling of a wind turbine system is presented as a by-product. To summarize, the proposed integrated fault estimation and fault tolerant control strategy can handle a system with highly nonlinear dynamics in a strong disturbance/noise environment (e.g., partially-decoupled process disturbances and stochastic parameter perturbations), which is validated by a real-time wind turbine system. As a result, the presented methods/algorithms have enriched fault diagnosis and tolerant control theory with high-novelty and great potentials for practical applications.

Active integrated antenna (MA) is a very popular topic of research during recent decades. This is mostly due to its advantages, such as compact size, multiple functions and low cost, etc. The MA system can be regarded as an active microwave circuit which the output or input port is free space instead of a conventional 50-ohm interface. The major drawbacks of the conventional MA include narrow bandwidth, low efficiency, etc. An experimental investigation on broadband slot-coupled antenna is carried out, which results an impedance bandwidth of 50 % is achieved by both a ring slot- coupled and square ring slot-coupled patch antenna. An improved design technique for broadband class-E power amplifier (PA) design, based on the theoretical analysis done by Mader [2], is introduced to calculate the circuit parameters. The technique is applied to a RF microwave class-E power amplifier design (PA) that results a bandwidth of 12 % power added efficiency (PAE) greater than 60 % is achieved. The aim of this work is to design broadband high efficiency linearly polarized (LP) and circularly polarized (CP) MA and arrays that will be useful for mobile communication system. The MA does not need conventional matching network between the amplifier and the antenna, because the antenna serves as both a harmonics-tuning network and a radiator. A novel high efficiency broadband LP MA is demonstrated using a ring slot-coupled patch antenna with a class-E PA. It exhibits a PAE over 50 % within a 14.6 % bandwidth. For the first time, a high efficiency broadband CP MA is designed using a class-E PA integrated with a broadband CP antenna. The CP AIA achieves a PAE over 50 % within a 14 % bandwidth. The axial ratio of the CP MA is below 3 dB over a 9 % bandwidth. For further improve the performance, a novel L-shaped slot-coupled broadband CP MA is employed in a 2x2 array. The array consists of four sequentially rotated broadband CP antenna elements with an element spacing of half a free space wavelength. The antenna was designed to operate in the 3G band around 2 GHz. A bandwidth of 22.7 % PAE greater than 50 % is achieved together with a peak PAE of 71.35%. A bandwidth of 27 % axial ratio below 3 dB is resulted.

This thesis presents the research carried out into the effects of load and source harmonic terminations on the efficiency of a class-F power amplifier (PA). A demonstration on the direct integration of the class-F PA and an H-shaped patch antenna using an active integrated antenna (AIA) approach is also presented. To obtain a high efficiency PA, it is necessary to ensure that the power dissipated in the active device is minimised and this is achieved by ensuring that the overlapping area between the drain voltage and current waveforms in the time domain is minimised. To minimise this overlapping area, optimum source and load harmonic impedances for the fundamental frequency, and second and third harmonics, are obtained using a novel application of the simulated load/source-pull method. New forms of harmonic matching networks were designed to ensure that the active device is terminated by the optimum impedances at the gate and drain for maximum efficiency. Three PAs were designed, one operating at 0.9 GHz and the other two at 2.45 GHz. For the 0.9 GHz PA the load matching network was designed to obtain the required optimum impedances at the fundamental frequency, and second and third harmonics. As the effect of gate capacitance is small at this frequency, the source matching network was designed to obtain a conjugate match at the fundamental frequency only. At the higher frequency of 2.45 GHz, the gate capacitance has a larger effect on the efficiency of the PA and hence two designs were investigated and compared. In the first PA design the load and source matching networks were designed to obtain optimum impedances at the fundamental frequency and second harmonic. For the second PA design, these networks were designed to obtain optimum impedances at the fundamental frequency, and second and third harmonics. For these three PAs the simulated drain voltage/current waveforms, return loss, stability factor, power gain, output power and power added efficiency (PAE) are presented. The practical results are compared with those obtained by simulation. Each PA produced a PAE of greater than 70% and good agreement was obtained between the simulated and measured results. The PAE obtained in these works is comparable to that reported in published papers. Based on this research five papers have been published in journals and conferences. An H-shaped microstrip patch antenna is used in the active integrated antenna (AIA) design. The antenna must not only act as a radiator and a harmonic suppresser but also as an optimum load for the PA so that it can be connected directly to the active device in order to obtain maximum efficiency. An extensive study on this antenna was carried out. The formulas for the first four mode frequencies were derived using odd and even mode analysis while a new and simpler formula for the fourth mode frequency was obtained. A systematic design approach to obtain the dimensions of the antenna is presented for an antenna operating at a given fundamental mode frequency. For matching, a new explicit matrix input impedance formula for the H-shaped antenna has been obtained using segmentation method. Using this formula, the location of the probe feed could be adjusted to obtain the required impedance at the pre-assigned frequency. MathCAD programming is used to implement the calculations in the design of two antennas. Good agreement between the predicted, simulated and measured results is obtained for the resonant mode frequencies, input impedance and return loss. Based on this research two papers have been published in journals.

This thesis investigates and analyses the performance of terrestrial free-space optical communication (FSO) system based on the phase shift keying pre-modulated subcarrier intensity modulation (SIM). The results are theoretically and experimentally compared with the classical On-Off keying (OOK) modulated FSO system in the presence of atmospheric turbulence. The performance analysis is based on the bit error rate (BER) and outage probability metrics. Optical signal traversing the atmospheric channel suffers attenuation due to scattering and absorption of the signal by aerosols, fog, atmospheric gases and precipitation. In the event of thick fog, the atmospheric attenuation coefficient exceeds 100 dB/km, this potentially limits the achievable FSO link length to less than 1 kilometre. But even in clear atmospheric conditions when signal absorption and scattering are less severe with a combined attenuation coefficient of less than 1 dB/km, the atmospheric turbulence significantly impairs the achievable error rate, the outage probability and the available link margin of a terrestrial FSO communication system. The effect of atmospheric turbulence on the symbol detection of an OOK based terrestrial FSO system is presented analytically and experimentally verified. It was found that atmospheric turbulence induced channel fading will require the OOK threshold detector to have the knowledge of the channel fading strength and noise levels if the detection error is to be reduced to its barest minimum. This poses a serious design difficulty that can be circumvented by employing phase shift keying (PSK) pre-modulated SIM. The results of the analysis and experiments showed that for a binary PSK-SIM based FSO system, the symbol detection threshold level does not require the knowledge of the channel fading strength or noise level. As such, the threshold level is fixed at the zero mark in the presence or absence of atmospheric turbulence. Also for the full and seamless integration of FSO into the access network, a study of SIM-FSO performance becomes compelling because existing networks already contain subcarrier-like signals such as radio over fibre and cable television signals. The use of multiple subcarrier signals as a means of increasing the throughput/capacity is also investigated and the effect of optical source nonlinearity is found to result in intermodulation distortion. The intermodulation distortion can impose a BER floor of up to 10-4 on the system error performance. In addition, spatial diversity and subcarrier delay diversity techniques are studied as means of ameliorating the effect of atmospheric turbulence on the error and outage performance of SIM-FSO systems. The three spatial diversity linear combining techniques analysed are maximum ratio combining, equal gain combining and selection combining. The system performance based on each of these combining techniques is presented and compared under different strengths of atmospheric turbulence. The results predicted that achieving a 4 km SIM-FSO link length with no diversity technique will require about 12 dB of power more than using a 4 × 4 transmitter/receiver array system with the same data rate in a weak turbulent atmospheric channel. On the other hand, retransmitting the delayed copy of the data once on a different subcarrier frequency was found to result in a gain of up to 4.5 dB in weak atmospheric turbulence channel.

Matching networks are widely used to enhance active power transfer when radio frequency generators drive complex loads. The tuning of the network for varying loads typically involves searching for optimum matching conditions. However, improving the matching condition of the network does not necessarily indicate an increase in active power transfer. As an example, a 71 network with three adjustable elements may achieve comparable matches for a variety of elements' settings, each matching triple exhibiting a different transferred active power. Furthermore, the influence of the transmission lines used to connect the matching network to its source and load is rarely taken into account. The purpose of the work is to optimise the power gain of a narrowband matching sys-tem in the frequency range of 1.8 — 30 MHz. The system consists of a source, a match-ing network, a load and two interconnecting lines whose characteristic impedance is complex. The optimisation process involves optimum choice of the transmission lines' lengths and development of a matching strategy. Its objective is to ensure automatic and continuous adjustment of the matching network for optimum ac¬tive power transfer to its load while matching the network's input impedance to a resistive source. The network topologies employed are limited to the most common 71 and T networks consisting of two variable capacitors and one central inductor. Losses are assumed to be mainly caused by the inductor. An appropriate simple and synthetic model of the losses is proposed which is suitable for active power transfer optimisation. The model is validated against losses of inductors derived by different works. After choosing a proper network parametrisation and exact inclusion of the losses during network design, the losses of a network terminated by a resistance and de¬signed to match (exactly) a source resistance at its input are derived. Then its power gain is optimised by a proper choice of the network's parameter and the impact of changing the purely resistive termination to impedances exhibiting capacitive or in¬ductive imaginary parts is considered. An explicit solution is calculated for networks with a constant Q factor central inductor, its differences from the approximate solu¬tion (network elements designed as if the network would be lossless) are considered. Example diagrams are given illustrating those differences and power gain contour Smith charts are drawn for typical ranges of the L, iv, and T networks' elements. Combining the results of the different approaches yields an optimum matching strat¬egy. The losses of transmission lines connecting source and network of load and network are determined, where the lines' complex characteristic impedance is taken into account. Those losses are included in a power gain optimisation of the complete matching system. Finally, an experimental setup is designed under which the matching strategy of the network is tested and validated.

This study investigates the use of error control code, discrete wavelet transform (DWT) and artificial neural network (ANN) to improve the link performance of an indoor optical wireless communication in a physical channel. The key constraints that barricade the realization of unlimited bandwidth in optical wavelengths are the eye-safety issue, the ambient light interference and the multipath induced intersymbol interference (ISI). Eye-safety limits the maximum average transmitted optical power. The rational solution is to use power efficient modulation techniques. Further reduction in transmitted power can be achieved using error control coding. A mathematical analysis of retransmission scheme is investigated for variable length modulation techniques and verified using computer simulations. Though the retransmission scheme is simple to implement, the shortfall in terms of reduced throughput will limit higher code gain. Due to practical limitation, the block code cannot be applied to the variable length modulation techniques and hence the convolutional code is the only possible option. The upper bound for slot error probability of the convolutional coded dual header pulse interval modulation (DH-PIM) and digital pulse interval modulation (DPIM) schemes are calculated and verified using simulations. The power penalty due to fluorescent light interference (FL I) is very high in indoor optical channel making the optical link practically infeasible. A denoising method based on a DWT to remove the FLI from the received signal is devised. The received signal is first decomposed into different DWT levels; the FLI is then removed from the signal before reconstructing the signal. A significant reduction in the power penalty is observed using DWT. Comparative study of DWT based denoising scheme with that of the high pass filter (HPF) show that DWT not only can match the best performance obtain using a HPF, but also offers a reduced complexity and design simplicity. The high power penalty due to multipath induced ISI makes a diffuse optical link practically infeasible at higher data rates. An ANN based linear and DF architectures are investigated to compensation the ISI. Unlike the unequalized cases, the equalized schemes don‘t show infinite power penalty and a significant performance improvement is observed for all modulation schemes. The comparative studies substantiate that ANN based equalizers match the performance of the traditional equalizers for all channel conditions with a reduced training data sequence. The study of the combined effect of the FLI and ISI shows that DWT-ANN based receiver perform equally well in the present of both interference. Adaptive decoding of error control code can offer flexibility of selecting the best possible encoder in a given environment. A suboptimal 'soft' sliding block convolutional decoder based on the ANN and a 1/2 rate convolutional code with a constraint length is investigated. Results show that the ANN decoder can match the performance of optimal Viterbi decoder for hard decision decoding but with slightly inferior performance compared to soft decision decoding. This provides a foundation for further investigation of the ANN decoder for convolutional code with higher constraint length values. Finally, the proposed DWT-ANN receiver is practically realized in digital signal processing (DSP) board. The output from the DSP board is compared with the computer simulations and found that the difference is marginal. However, the difference in results doesn‘t affect the overall error probability and identical error probability is obtained for DSP output and computer simulations.

This thesis presents the findings of an investigation into hybrid mode feed horns for use in the next generation of reflector antennas for satellite communications at Ka- band. Within the thesis, general field theory is developed and subsequently applied to specific horn-types in an effort to understand and explore the limits of the bandwidth over which they can offer suitable radiation characteristics. Studies into the use of both corrugated and dielectric-loaded horns identify a shortfall in their performance, particularly in the context as feeds for elliptical reflector antennas at Ka-band, as a consequence of the sizeable frequency separation between the Transmit and Receive functions. The need to operate at two widely separated bands, with little concern for the performance at all frequencies in between, affords the opportunity to take advantage of two exclusive mechanisms to independently optimise the performance at two sub- bands, corresponding to the Transmit and Receive functions. The 'dual-band' concept is explored by extending the field theory developed earlier in the thesis, this being applied to a corrugated structure with secondary mechanism that takes effect once the performance as a consequence of the corrugations themselves begins to degrade. The theory is tested by way of a practical investigation comparing the measured performance of different horn types, including a novel horn borne out of the dual- band concept described above. This led to the need to develop, construct and evaluate a suitable anechoic chamber, the work associated with this also being included in the thesis as an appendix. The results are reviewed in the context of the Ka-band application against both RF and practical design goals with the conclusion that the novel dual-band horn offers superior performance with respect to the state-of-the-art.

The oxidation behaviour of Fe3A1 intermetallic alloys with and without reactive element (RE) and Ti-46.7A1-1.9W-0.5Si alloy over the temperature ranges of 900 to 1100°C and 750 to 950°C respectively were studied for up to 240h. The isothermal and cyclic oxidation behaviour of Fe3A1 intermetallic materials was studied in static air. The Al203 adherence of (Y and/or Hf)-doped Fe3A1 alloys was examined using newly developed — by the researcher — cyclic oxidation rig built in AMRI's laboratory. However the oxidation of Ti-46.7A1-1.9W-0.5Si alloy was studied in air and under Ar-02 atmospheres of three oxygen partial pressures; P02 = (0.05, 0.2 and 0.8) x 105 Pa. Isothermal sulphidation/oxidation work of coated — with specially designed single and multi- layer coatings — and uncoated Ti-46.7A1-1.9W-0.5Si alloy was performed in relatively high partial pressure of sulphur (pS2 = 6.8 x 10-1 Pa) and low partial pressure of oxygen (p02 = 1.2 x 10-15 Pa) at 850° C for up to 240h. Characterisation of the specimens was conducted using SEM, EDX, and XRD techniques. Higher oxidation rates of Ti-46.7A1-1.9W-0.5Si alloy were observed in air than in Ar-20%02 at all temperatures. The scale formed in air consisted of Ti02/Al203/Ti02/TiN/TiAl2/substrate, whilst the scale developed in Ar-20%02 atmosphere was comprised of Ti02/Al203/Ti02/Al203/Ti3A1/substrate. The oxidation rates of Ti-46.7A1-1.9W¬0.5Si alloy increased with decreasing the oxygen partial pressure in Ar-02 atmospheres at the entire range of temperatures. The employment of single A1TiN and CrN single layer coatings improved the sulphidation/oxidation behaviour of Ti-46.7A1-1.9W-0.5Si alloy at 850°C for up to 240h in H2/H20/H2S gas mixture. However, the use of NbN and CrN diffusion barrier coatings significantly enhanced its corrosion resistance. The scale on uncoated Ti-46.7A1-.9W-0.5Si alloy in sulphidising/oxidising atmosphere consisted of Ti02/Al203/TiS+W/TiA13/TiAl2/substrate. The reactive element (RE) — Y and/or Hf — addition especially Y significantly improved the oxide adherence of Fe3A1 over the specified range of temperature and exposure time (or cycles). However, higher oxidation rate of Fe3A1 alloys doped with Y was obtained under both isothermal and cyclic oxidation. Although the scale thickness of Hf-doped alloy was always higher than that of Y-doped alloys, the oxidation rate constant of the later is found in some cases to be less than that of the first by one order of magnitude. However, the scale on the Hf-doped alloy is relatively adherent to the substrate if compared with the scale of undoped Fe3A1 alloy even at the areas where oxide pegs were observed on Fe3A1-Hf alloy. Generally, no conclusion could be taken from the kinetic data of Fe3A1 alloys regarding the reactive element effect (REE) due to the intergranular attack on the Y-containing alloys. Improving the interface properties by RE addition led to a better control of the outward diffusion of aluminium and eliminated the detrimental effect of sulphur (possibly present in the Fe3A1 alloys). However, the presence of the RE in the alloy led to the formation of coherent scales. At 1100°C and after prolonged exposure, the scale of RE- doped alloys was not able to remain in contact with the substrate especially under thermal cycling conditions. The external scale severely cracked especially at places where oxide ridges were formed. The Y-containing Fe3A1 alloys were capable of producing another thin and adherent scale underneath the cracked external scale.