This thesis describes work on the growth and electrical properties of thin luminescent films of zinc silicate phosphor, Zn(_2)Si0(_4) : Mn, formed from the solid-state reaction of ZnF(_2):Mn and Si0(_2) at 1000ºC, on n-type silicon substrates. The film formed in this way consists of zinc silicate separated from the silicon by a non-luminescent interfacial layer. Electrical measurements were made on metal-insulator- silicon (MIS) capacitors formed by photolithography using both the composite and the interfacial film as the insulator. The film properties vary with the growth conditions. Three types of films, defined by the gas ambient for the reaction, were investigated. High frequency capacitance-voltage measurements on the composite films showed good MIS-type characteristics but with flat-band voltages that changed with electrical stress. These changes, together with measurements made on the interfacial layers, were used to study the formation of space-charge within the films. Films formed in short reaction times in N(_2) and those with longer reaction times in 10% of 0(_2) in N(_2), showed polarization when negatively stressed at 10(^5) v/cm and above. This was explained by the build-up of negative space-charge at the dielectric - dielectric interface, due to the separation of Zn(^2+) cations from the immobile (Si0(_4))(^4-) anions in the silicate, close to the interface. Films formed by a long reaction time in ultra-pure N(_2), showed the above type of polarization phenomenon only in a very thin outer layer. However, in the bulk, polarization was probably due to charge accumulation at crystallite boundaries. In general, there is ho strong evidence of electron injection into the silicate films.

The properties of nonlinear devices, semiconductor diodes, were determined at high frequencies using the method of spectral characterisation. Such characterisation was carried out employing a specially developed technique where the components of the harmonic spectrum generated within these diodes at radio and microwave frequencies were measured. The theory of spectral analysis, based on Fourier principles, was reviewed. It was applied to the periodic gate function, which plays a fundamental role in signal analysis, in order to lay the foundation for the theoretical investigation carried out between pulses of known shapes and their corresponding spectra. Some useful relationships were established and applied in the evaluation of devices. Based on the fundamental properties of the periodic gate function, two new sampling procedures were introduced. The harmonic generating properties of practical diodes, where the nonlinearity in the element is an inherent condition, were examined. It was established that the spectrum generated within the device, at a particular drive level, gives the "fingerprint" of the diode, i.e. represents fully its nonlinearity. Measurement methods, both at low and high frequencies, were also discussed. The new technique, called the Multiple Reflections Resonant Line (MRRL) method was developed and described in the thesis to measure a complete spectrum. The method employed a coaxial slotted line system terminated by the device under test. The basic transmission line theory was extended to include the phenomena of multiple reflections along and resonance of, the line. The properties of the standing waves were then related to the device parameters. The twelve microwave diodes were successfully modelled which included parasitics using the new spectral technique. An attempt was made to evaluate these devices for particular applications.

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This thesis describes a mathematical and experimental study of circular arrays of directional antennas. For directional pattern synthesis in circular arrays of omnidirectional elements, mode-analysis or Fourier harmonic analysis technique has previously been used. This thesis describes the effect of using any directional element on the mode properties - in the horizontal plane, and on the vertical directional pattern of such arrays. The effect of random amplitude and phase errors in the excitation of circular arrays and of mutual coupling with reference to directional pattern synthesis is also studied. A procedure is outlined for designing circular arrays of directional elements and a design of an experimental 16- element circular array is then presented. This is an 8 foot diameter array of 16 wideband elements each having a pattern of the form (l+cosφ) for operation at 200-400MHz frequency band. Various mode patterns are computed for the array to determine their purity. The theoretical wideband performance of the array is also examined. New techniques are described for the synthesis of single and 2n sharp nulls in otherwise omnidirectional patterns of circular arrays and the mechanism for independent steering of these nulls is also described. Patterns are computed to demonstrate and theoretically study the techniques. Finally, experimental results are presented to complement the theoretical study of circular arrays and null patterns.

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A survey is made of past work associated with the indirect lightning stroke in relation to the 11 kV rural electricity supply network in this conntry. Facts are established which are considered relevant to this specific type of system with pulse excitation. A complementary field study, based on extensive lightning fault records of a particularly affected area, provides sufficient evidence to establish a characteristic pattern of behaviour to be expected from the network. Each faulted circuit is assumed to be made up of several basic topologies, which are considered as lossless elements, on which single conductor surge analysis is performed by means of a graphical method devised by Bergeron. This is regarded as an efficient first stage assessment of the propagation response, and may be directly compared with the pattern of responses in the field study to explain thosee fault processes due to simple travelling waves alone. The preparation and analysis of a three-conductor circuit is also given some attention. To account for the frequent appearance of anomalous faults, some consideration is given to the influence of local topography associated with the fault, and to a further source of excitation in the form of the prestrike charge which has hitherto been neglected. The study ends with suggestions for the continuation of the work.