This thesis investigates some of the challenges involved in developing technology for a hypothetical lightweight multifunction radar system incorporating element level digitisation. The benefits of a digital array are well understood, but development of the technologies involved has been slow. Market drivers for this type of system are reviewed from the perspective of SELEX Galileo and the state of the art for existing and emerging technologies are explored. There follows an investigation of potential architectures for an element-level receiver in which the merits of different approaches are compared, leading to a recommendation for the most appropriate architecture for a commercial system. Alternative implementations of this receiver are discussed and compared, including making use of consumer technology as an alternative to custom microwave integrated circuits. This concludes with a proposal for the further work required to produce a prototype receiver. Finally, a novel filter aimed at solving a specific problem in existing radar architectures is developed and its performance demonstrated through simulation. Throughout the work, close attention is paid to key technology barriers that limit further advancement in the matters considered.

Spread Spectrum (SS) communication, initially designed for military applications, is now the basis for many of today's advanced communications systems such as Code Division Multiple Access (CDMA), Global Positioning System (GPS), Wireless Local Loop (WLL) , etc. For effective communication to take place in systems using SS modulation, the Pseudo-random Noise (PN) code used at the receiver to despread the received signal must be identical and be synchronised with the PN code that was used to spread the signal at the transmitter. Synchronisation is done in two steps: coarse synchronisation or acquisition, and fine synchronisation or tracking. Acquisition involves obtaining a coarse estimate of the phase shift between the transmitted PN code and that at the receiver so that the received PN code will be aligned or synchronised with the locally generated PN code. After acquisition, tracldng is now done which involves maintaining the alignment of the two PN codes. This thesis presents results of the research calTied out on a proposed adaptive PN code acquisition circuit designed to improve the synchronisation process in Direct Sequence CDMA (DS-CDMA) systems. The acquisition circuit is implemented using a Matched Filter (MF) for the correlation operation and the threshold setting device is an adaptive processor known as the Cell Averaging Constant False Alarm Rate (CA-CFAR) processor. It is a double dwell acquisition circuit where the second dwell is implemented by Post Detection Integration (PDI). Depending on the application, PDI can be used to mitigate the effect of frequency offset in non-coherent detectors and/or in the implementation of multiple dwell acquisition systems. Equations relating the performance measures - the probability of false alarm (Pra ), the probability of detection (P d) and the mean acquisition time (E {Tacq}) - of the circuit are deri ved. Monte Carlo simulation was used for the independent validation of the theoretical results obtained, and the strong agreement between these results shows the accuracy of the derived equations for the proposed circuit. Due to the combination of PDI and CA-CFAR processor in the implementation of the circuit, results obtained show that it can provide a good measure of robustness to frequency offset and noise power variations in mobile environment, consequently leading to improved acquisition time performance. The complete synchronisation circuit is realised by using this circuit in conjunction with a conventional code tracking circuit. Therefore, a study of a Non-coherent Delay-Locked Loop (NDLL) code tracking circuit is also calTied out.

The two most important trends in electronic industry are "miniaturisation" and "increased functionality". Over the last fifteen years, the electronic manufacturing industries have experienced tremendous pressure to meet the requirements for miniaturised products, particularly, hand-held consumer products. Functionality of these products has also evolved at the same pace through packing in more and more features. As these trends are set to continue, there is an increasing demand for better understanding of soldering technology, particularly in the area of solder pastes used in the reflow soldering of surface mount devices. Successful assembly of electronic devices for ultra-fine pitch and flip-chip applications requires the deposition of small and consistent paste deposits from pad to pad, and from board to board. The paste printing process at this chip-scale geometry depends on conditions such as good paste roll, complete aperture filling and paste release from the apertures onto the substrate pads. This means that the paste flow and deformation behaviour is very important in defining the printing performance of any solder paste. In order to understand rheological phenomena associated with the flow of solder pastes, it is necessary to understand time dependent rheological behaviour. Such behaviour is common to many industrial fluids and consequently has been of interest to rheologists for many years. The time dependent behaviour observed in solder pastes is largely due to the breakdown of the flocculated structure formed during storage or idle period. In general, the breakdown of the structure with shear results in a decrease in apparent viscosity. Recovery after shear is generally a very slow process and depends on the intensity of the breakdown and previous shear history. The work reported in this thesis on the characterisation and modelling of time-dependent rheological behaviour of solder paste and flux mediums used in surface mount applications is made up of four main parts. The first part concerns the characterisation of the time-dependent behaviour of solder pastes and flux mediums. Two types of tests were performed at this stage: hysteresis-loop test and step-shear-rate test. In the second part of the study the time-dependent rheology of solder pastes and flux mediums has been modelled to evaluate the mechanisms for the break-down of the internal structure of the paste materials. A novel technique has been developed which combines the experimental rheological data with a modified structural kinetic model (SKM) to investigate the rate and extent of structural change of solder paste and flux medium. The third part of the study deals with the experimental and modelling studies of the short term build-up of solder paste and flux medium structure using the stretched exponential model. In the final part of the study the printing trials of four different solder paste samples were carried out to investigate the effect of post-print rest period on slumping behaviour of solder paste. From the experimental characterisation it was evident that both the solder paste and flux samples are strongly thixotropic and shear-thinning in nature. The thixotropic breakdown behaviour of solder paste and fluxes has been satisfactorily modelled using a second-order structural kinetic model. The results from this study can be of great help for the solder paste manufacturers and formulators in quantifying and predicting the effect of long term shearing on the solder paste samples. The technique developed can also be utilized for similar materials such as solar pastes and conductive adhesives. The short-term build-up of solder pastes and fluxes has been successfully modelled using the stretched exponential model. The paste manufacturers and formulators can use the technique developed to predict and quantify the slumping behaviour of solder paste. The end-users, for example the electronics assemblers may use the technique to optimize their assembly process by minimising/preventing slumping of solder paste.

This thesis is an overview of a number of investigations on antenna systems and related subjects over a period of 28 years, which has resulted in 44 publications in the technical literature, one current patent, and an M.Sc. thesis. The investigations have been grouped into 7 categories: - Log periodic antennas, - Antenna performance measurement techniques, - Spacecraft Antenna Systems, - Satcom Terminal Antennas, - Transmission lines and baluns, - High Radar Cross Section Reflectors for Spaceborne Radar Calibration, - Miscellaneous Antenna Investigations. These investigations have resulted in various outcomes: in new antenna types and in improved antenna configurations; in improved techniques for antenna rf performance evaluation; in new knowledge relating to materials used with spacecraft antenna systems; in the development of computer software and computer-numerical methods for specific purposes; and in the advancement of accurate radar cross section prediction methods for spaceborne radar calibration targets. In the discipline of log-periodic antennas, a planar 'printed circuit 1 antenna structure has been devised which has a toroidal shaped radiation pattern distribution with horizontal linear polarization. A non-planar form of this radiating structure with a unidirectional beam has also been demonstrated. Some new techniques for measuring the rf characteristics of antenna systems have been devised. These include special techniques for frequency scaled ship model hf radar antenna measurements, and techniques for measuring scattering from the feed support struts of large Earth station parabolic reflector antennas. A novel method of acquiring near field phase and amplitude data using an interference technique for determining antenna far field performance characteristics by near field to far field data processing transformation has been demonstrated. Correction factors which allow gain comparison measurements to be made in short range length facilities, such as certain types of anechoic chamber, have also been presented. Antenna measurement techniques which are applicable to spacecraft antenna systems have been reviewed. With regard to spacecraft antenna systems, a number of diverse studies have been carried out, one of which has resulted in the composition of a mathematical procedure for predicting the complex beamshapes of contoured beam satellite reflector antenna systems. Also, experimental work has been described which showed that spacecraft reflector antennas constructed with carbon fibre reinforced plastics do not require metallic surface coatings, and that thermal control paint applied to spacecraft does not cause antenna performance degradation. Other programmes of research involved VHP turnstile antenna systems on large satellites, and future technology, geostationary orbit multi-role satellites with 'plug-in' payloads. New satcom terminal antenna configurations has been a very important area of research, resulting in high performance circularly polarized antenna configurations for small terminals for maritime, aeronautical and land-mobile applications. A patent has also been granted on a very compact antenna system for a satellite paging receiver. Many types of antenna require a balun system of some type, often with impedance transformation, for excitation of the radiating elements. A mathematical analysis which allows the design of one type of impedance transforming balun has been presented, and a new microstrip and coaxial cable balun system with progressive quadrature phase output (for the excitation of quadrifilar antennas) has been demonstrated. Very large radar cross section (RCS) passive radar reflectors are used for the monostatic calibration of spaceborne synthetic aperture radars on Earth resource monitoring satellites. A computer-numerical technique for accurately determining the RCS of these large reflectors was devised and has been extensively used. Other aspects of large radar reflector operation were also investigated, such as RCS reduction due to construction errors and radome covers Publications relating to a number of other miscellaneous antenna investigations are also included in this thesis. Among these are descriptions and performance details of choked waveguide and printed dipole feeds for parabolic reflector antennas, a special purpose antenna for a remotely piloted vehicle, and some results from an investigation on a double offset reflector antenna system. The publications which are the subject of this thesis, are introduced here in their historical context, and are presented in the Appendix at the back of this volume.

With the increased complexity of Very Large Scaled Integrated (VLSI) circuits, multilevel logic synthesis plays an even more important role due to its flexibility and compactness. The history of symbolic logic and some typical techniques for multilevel logic synthesis are reviewed. These methods include algorithmic approach; Rule-Based approach; Binary Decision Diagram (BDD) approach; Field Programmable Gate Array(FPGA) approach and several perturbation applications. One new kind of don't cares (DCs), called functional DCs has been proposed for multilevel logic synthesis. The conventional two-level cubes are generalized to multilevel cubes. Then functional DCs are generated based on the properties of containment. The concept of containment is more general than unateness which leads to the generation of new DCs. A separate C program has been developed to utilize the functional DCs generated as a Boolean function is decomposed for both single output and multiple output functions. The program can produce better results than script.rugged of SIS, developed by UC Berkeley, both in area and speed in less CPU time for a number of testcases from MCNC and IWLS'93 benchmarks. In certain applications ANDjXOR (Reed-Muller) logic has shown some attractive advantages over the standard Boolean logic based on AND JOR operations. A bidirectional conversion algorithm between these two paradigms is presented based on the concept of polarity for sum-of-products (SOP) Boolean functions, multiple segment and multiple pointer facilities. Experimental results show that the algorithm is much faster than the previously published programs for any fixed polarity. Based on this algorithm, a new technique called redundancy-removal is applied to generalize the idea to very large multiple output Boolean functions. Results for benchmarks with up to 199 inputs and 99 outputs are presented. Applying the preceding conversion program, any Boolean functions can be expressed by fixed polarity Reed-Muller forms. There are 2n polarities for an n-variable function and the number of product terms depends on these polarities. The problem of exact polarity minimization is computationally extensive and current programs are only suitable when n :::; 15. Based on the comparison of the concepts of polarity in the standard Boolean logic and Reed-Muller logic, a fast algorithm is developed and implemented in C language which can find the best polarity for multiple output functions. Benchmark examples of up to 25 inputs and 29 outputs run on a personal computer are given. After the best polarity for a Boolean function is calculated, this function can be further simplified using mixed polarity methods by combining the adjacent product terms. Hence, an efficient program is developed based on decomposition strategy to implement mixed polarity minimization for both single output and very large multiple output Boolean functions. Experimental results show that the numbers of product terms are much less than the results produced by ESPRESSO for some categories of functions.

In this thesis, a variety of algorithms for synthesis and optimisation of combinational and sequential logic circuits are developed. These algorithms could be part of new commercial EGAD package for future VLSI digital designs. The results show that considerable saving in components can be achieved resulting in simpler designs that are smaller, cheaper, consume less power and easier to test. The purpose of generating different sets of coefficients related to Reed Muller (RM) is that they contain different number of terms; therefore the minimum one can be selected to design the circuits with reduced gate count. To widen the search space and achieve better synthesis tools, representations of Mixed Polarity Reed Muller (MPRM), Mixed Polarity Dual Reed Muller (MPDRM), and Pseduo Kronecker Reed Muller (PKRO RM) expansions are investigated. Efficient and fast combinatorial techniques and algorithms are developed for the following: â Bidirectional conversion between MPRM/ MPDRM form and Fixed Polarity Reed Muller forms (FPRM)/Fixed Polarity Dual Reed Muller forms (FPDRM) form respectively. The main advantages for these techniques are their simplicity and suitability for single and multi output Boolean functions. â Computing the coefficients of any polarity related to PKRO_RM class starting from FPRM coefficients or Canonical Sum of Products (CSOP). â Computing the coefficients of any polarity related to MPRM/or MPDRM directly from standard form of CSOP/Canonical Product of sums (CPOS) Boolean functions, respectively. The proposed algorithms are efficient in terms of CPU time and can be used for large functions. For optimisation of combinational circuits, new techniques and algorithms based on algebraic techniques are developed which can be used to generate reduced RM expressions to design circuits in RM/DRM domain starting from FPRM/FPDRM, respectively. The outcome for these techniques is expansion in Reed Muller domain with minimal terms. The search space is 3`" Exclusive OR Sum of Product (ESOP)/or Exclusive NOR Product of Sums (ENPOS) expansions. Genetic Algorithms (GAs) are also developed to optimise combinational circuits to find optimal MPRM/MPDRM among 3° different polarities without the need to do exhaustive search. These algorithms are developed for completely and incompletely specified Boolean functions. The experimental results show that GA can find optimum solutions in a short time compared with long time required running exhaustive search in all the benchmarks tested. Multi Objective Genetic Algorithm (MOGA) is developed and implemented to determine the optimal state assignment which results in less area and power dissipation for completely and incompletely specified sequential circuits. The goal is to find the best assignments which reduce the component count and switching activity simultaneously. The experimental results show that saving in components and switching activity are achieved in most of the benchmarks tested compared with recently published research. All algorithms are implemented in C++.

Evolvable Hardware (EHW), as an alternative method for logic design, became more attractive recently, because of its algebra-independent techniques for generating selfadaptive self-reconfigurable hardware. This thesis investigates and relates both evaluation and evolutionary processes, emphasizing the need to address problems arising from data complexity. Evaluation processes, capable of evolving cost-optimised fully functional circuits are investigated. The need for an extrinsic EHW approach (software models) independent of the concerns of any implementation technologies is emphasized. It is also shown how the function description may be adapted for use in the EHW approach. A number of issues of evaluation process are addressed: these include choice of optimisation criteria, multi-objective optimisation tedmiques in EHW and probabilistic analysis of evolutionary processes. The concept of self-adaptive extrinsic EHW method is developed. This approach emphasizes the circuit layout evolution together with circuit functionality. A chromosome representation for such system is introduced, and a number of genetic operators and evolutionary algorithms in support of this approach are presented. The genetic operators change the genetic material at the different levels of chromosome representation. Furthermore, a chromosome representation is adapted to the function-level EHW approach. As a result, the modularised systems are evolved using multi-output building blocks. This chromosome representation overcomes the problem of long string chromosome. Together, these techniques facilitate the construction of systems to evolve logic functions of large number of variables. A method for achieving this using bidirectional incremental evolution is documented. It is demonstrated that the integration of a dynamic evaluation process and self-adaptive function-level EHW approach allows the bidirectional incremental evolution to successfully evolve more complex systems than traditionally evolved before. Thereby it provides a firm foundation for the evolution of complex systems. Finally, the universality of these techniques is proved by applying them to multivalued combinational logic design. Empirical study of this application shows that there is no fundamental difference in approach for both binary and multi-valued logic design problems.

The success of modelling partially magnetised linear 3-port junction circulator, which is non-uniformly biased, depends chiefly on the precise representation of the strength of the intrinsic magnetic field in the axial direction across the ferrite material placed at the centre of the junction. The inadequateness of using conventional Polder tensor, which is established with the assumption that the ferrite material is saturated by a constant uniform magnetic field, in modelling partially and non-uniformly magnetised 3-port ferrite junction circulators is presented. It is proposed that the combination of static and microwave finite element (FE) solver overcomes the limit of Polder tensor in modelling partially and non-uniformly magnetised ferrite junction circulator. The proposed combination method requires the generation of the steady magnetic field in a magnetostatic solver, where the magnetic state of the ferrite material is determined, and the information of the static magnetic field of ferrite junction is transferred to the microwave solver for use in the microwave permeability tensor of the partially magnetised ferrite junction. Using the coupling method, the reflection coefficient responses of the 3-port ferrite junction circulator are determined in the low field loss region which coincides with the partially magnetised region and accompanies a few undesirable problems in communication systems, such as the reduction of bandwidth, and intermodulation product interference. The determined reflection coefficient is used to obtain the split frequencies which are important in designing and analysing the performance of a 3-port ferrite circulator in partially magnetised region. The main modelling factors considered are the effects from the number of mesh, the type of the magnetic field, the biasing configurations and the value of the dielectric constant. In each case, various split frequencies are obtained and, by considering all factors step by step, optimal modelling conditions are decided. The modelling results are compared with the experiment and show good agreement.

Once energised, and even when the equipment is not imaging, magnets used in magnetic resonance imaging will produce a static magnetic field that extends in three dimensions around the magnet. This static magnetic field is invisible; it is impossible to know that it is present or to be aware of it unless told. It is important to know the position and magnetic flux density of the static magnetic field because those persons having ferromagnetic material embedded within their bodies or their eyes (the result of a welding process for example), or fitted with electronic body implants, could suffer harm from the effects of the static magnetic field at relatively low levels. Those individuals fitted with some heart pacemakers could be affected at 0.5 mT. The published literature relating to magnetic resonance imaging is, by its nature, restricted to the medico-technical-academic press and does not systematically appear in publications destined for construction professionals. There is no published literature relating to the design of magnetic shielding for MRI suites as it relates to health and safety risks to those exposed to the static magnetic field during the construction, maintenance and demolition phases of a magnetic resonance imaging project. This thesis is progressive in its structure and fills gaps in knowledge by commencing with a study to determine if the requirements placed on duty holders as defined by The Construction (Design and Management) Regulations 2007 (CDM) and its antecedent regulations are understood by all those parties involved with the conception, design, construction and maintenance of an MRI suite. Several misconceptions are highlighted. A second study gave an evaluation of the availability of as-built drawings showing the position of the 0.5 mT footprint of the static magnetic field of the magnet and gives disappointing results. The third study was to assess the effectiveness of a retrofit installation of passive magnetic shielding and highlights some failings, with the fourth study to investigate if magnetic shielding had been installed to an operational MRI suite. The fifth study was to review if the client had considered the magnetic shielding design requirements of a magnet before it was installed. Finally, the sixth case study was to evaluate if there was a clear understanding by designers of the function and attributes of RF shielding and of passive magnetic shielding to a Faraday cage. Examples, by the inclusion of annotated drawings, are given. There was not a clear understanding by CDM duty-holders of responsibilities placed upon them under the CDM Regulations. The introduction of magnetic shielding into a magnetic resonance suite design can distort the symmetry of the 0.5 mT footprint of the static magnetic field, create areas of increased magnetic flux density and push parts of the 0.5 mT footprint to the outside of any designated controlled area. This will consequentially increase the risk of unscreened persons (both inside and outside the control of the employer) being exposed to the effects of the static magnetic field unless the magnitude and position of the 0.5 mT footprint is documented and disseminated to all those persons likely to come into contact with it. The incorporation of magnetic shielding as retrofit can result in leakages of magnetic flux at its joint with the finished floor and through any shielding fixing bolts. This thesis could be useful to designers in developing risk management plans for MRI suite construction, maintenance and demolition. By making a synthesis that has not been made before, this thesis makes a contribution to knowledge by addressing these issues for the first time.

Research already carried out on the use of the recently patented electroless nickel ceramic codeposition technique as a method of manufacturing solid oxide fuel cell (SOFC) electrodes has thus far indicated that, while functional electrodes can be manufactured by the technique, for optimum performance of the cell, amplification of the ceramic content of the coatings is still required. By mainly employing external agents such as surface active agents (surfactants) and magnetic fields (in a bid to aid ceramic particle stability), this research focused on the prospect of increasing the ceramic content of cermets co-deposited for use as SOFC electrodes. A total of 137 co-deposited samples were produced from different bath compositions. As a prelude to the study, the interactions between the ceramic powders used (yttria stabilised zirconia (YSZ) / lanthanum strontium manganate (LSM)) and the medium for the deposition process – the electroless nickel solution, were investigated by zeta potentiometry and ultraviolet-visible spectroscopy techniques. The results obtained from the studies led to a variation of a series of fundamental plating factors such as the ceramic bath loading and particle size of the powders. While the former was found to yield the highest ceramic content in the coating at a bath loading of 50 g/l, variation of latter notably produced mixed results. With the introduction of surfactants, it was noted that above the surfactant's (sodium dodecyl sulphate) critical micelle concentration, the incorporation of ceramic particles (YSZ) into the nickel matrix steadily increased to as much as 60 volume %. An inverse relationship was though found to exist between the coating thickness and the surfactant's bath concentration. Uniform coatings were found to be associated with low magnetic field strengths while although increased magnetic field strengths positively resulted in the amplification of particle incorporation into the coating, a lack of cohesion between the coating and the substrate – as indicated by coating flake-off, was observed at such strengths. It is suggested that because the magnetic flux was more dominant than the normally ionic plating mechanism, the particles co-deposited under the influence of a high magnetic field were relatively unstable after the coating process. Since LSM is alkaline in nature this work confirms that future research on the application of electroless nickel ceramic co-deposition as a method of manufacturing SOFC cathodes, be focused on the use of alkaline electroless nickel baths rather than the acidic solutions, which better suite YSZ particles.