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The transmission media, that is, the atmosphere, through which terrestrial and satellite signals traverse, is irregular. Thus, one requires proper knowledge on how variations in atmospheric refractive conditions will affect the optimal performance of terrestrial and satellite links. Under clear-air conditions, atmospheric changes will mainly involve variations in atmospheric pressure, relative humidity and temperature, which are the key to defining the way signals are refracted as they travel from the transmitter to the receiver. Accurate knowledge of these variations can be acquired through proper modeling, characterization and mapping of these three atmospheric quantities, in terms of the refractive index, refractivity gradient or the effective earth radius factor (k-factor). In this dissertation, both parametric and non-parametric modeling and characterizing, interpolation and mapping of the k-factor for South Africa is done. Median (k50%) and effective (k99.9%) k-factor values are the ones that determine antenna heights in line of sight (LOS) terrestrial microwave links. Thus, the accurate determination of the two k-factor values is critical for the proper design of LOS links by ensuring that adequate path clearance is achieved, hence steering clear of all obstacles along the radio path. Thus, this study is critical for the proper design of LOS links in South Africa. One parametric method (curve fitting) and one non-parametric method (kernel density estimation) are used to develop three-year annual and seasonal models of the k-factor for seven locations in South Africa. The integral of square error (ISE) is used to optimize the model formulations obtained in both cases. The models are developed using k-factor statistics processed from radiosonde measurements obtained from the South African Weather Service (SAWS) for a three year period (2007-2009). Since the data obtained at the seven locations is scattered, three different interpolation techniques are then explored to extend the three-year annual and seasonal discrete measured k-factor values for the seven locations studied to cover the rest of the country, and the results of the interpolation are then presented in the form of contour maps. The techniques used for the interpolation are kriging, inverse distance weighting (IDW) and radial basis functions (RBFs). The mean absolute error (MAE) and the root mean square error (RMSE) are the metrics used to compare the performance of the different interpolation techniques used. The method that produces the least error is deemed to be the best, and its interpolation results are the ones used for developing the contour maps of the k-factor. / M. Sc. Eng. University of KwaZulu-Natal, Durban 2013.

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Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 241-248). Available also in a digital version from Dissertation Abstracts.

To determine microwave usage patterns, a telephone survey was administered to 300 college students living off campus. The objectives of the study were to determine: a) incidence of ownership, b) characteristics of students who have a microwave oven and those that do not, c) patterns of use of microwave ovens, and d) characteristics of the present microwave oven and one desired in the future. Rogers’ Adoption Process was used as the model to determine that each owner had adopted the appliance into their lifestyle. The adoption stage was divided into three use levels: primary appliance used for cooking, appliance used as a supplement to the ranges and appliance used infrequently. It was found that 192 (64%) of the 300 participants had a microwave oven in there household and 237 (79%) would make a purchase of an appliance in the future. The microwave ovens that are currently owned have an average of 4.2 features including a minute timer, variable power, automatic defrost, and touch controls. Students who would purchase a microwave in the future desired an average of 7.2 features, minute timer, variable power, automatic defrost, touch controls, clock, and delay start. The tasks that are currently being performed in the microwave were divided into low, medium, and high complexity. Students using their microwaves more than their range prepare the most medium and low complexity foods, while owners who use their microwave as a supplement to their range prepare the greatest number of high complexity foods. Participants in all levels of adoption were satisfied with foods prepared in the microwave most of the time. Information from this study would be relevant to microwave manufacturers, residential property development corporations, and designers of food products and container. / Master of Science

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The conventional planar micro transformers presented very low quality-factor (Q<10) and very high insertion loss (-6 ~ -10 dB) at high operation frequency since most of the microwave power is dissipated through the silicon substrate. To increase the quality-factor and reduce the insertion loss of silicon-based transformers, this dissertation presents a two-port and three-port micro transformers with suspending structure utilizing the micro-electro-mechanical systems (MEMS) technology. The proposed silicon-based transformers are constructed by two winding and suspending micro inductors. Each suspending micro inductor consists of a 0.32 &#x00B5;m-thick TaN/Ta/Cu bottom electrode, a 10 &#x00B5;m-height supporting copper vias and a 6 &#x00B5;m-thick spiral copper conducting layer. This research adopts the Taguchi method and commercial electromagnetic simulation software (Ansoft-HFSS) to optimize the dimensional specifications of the copper conducting layer. Many high frequency characteristics of the suspending micro transformers are simulated, including the inductance, the magnetic coupling factor, the quality-factor, the magnitude imbalance, the phase imbalance, the common mode rejection ratio (CMRR) and the insertion loss. In this research, the surface micromachining and electrochemical deposition techniques are used to implement the suspending micro transformers. The main fabrication steps include five photolithography and eight thin-film deposition processes. According to the simulation and measurement results from the commercial network analyzer (Agilent-E8364B) and software (Agilent-ADS), the implemented two-port transformer demonstrates a high magnetic coupling factor (0.78) and a very high quality-factor (Q=17.20) at 5.2 GHz. On the other hand, the proposed three-port transformer presents a low magnitude imbalance (-0.02 dB), a low phase imbalance (1.65¢X), a high CMRR (36.78 dB) and a very low insertion loss (-4.52 dB) under the same operation frequency. In this dissertation, a novel suspending micro transformer has been developed and characterized. The proposed micro transformer is very suitable for being used in the portable microwave communication system due to its small chip size (0.7 mm¡Ñ0.7 mm¡Ñ0.5 mm) and excellent high-frequency characterization.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Nowadays, demands for fully integrated and miniaturized RFIC (Radio Frequency Integrated Circuits) have increased in wireless microwave communication system. Passive components such as coupler, divider and filters are always fabricated in outside of ICs due to their bulky sizes, which have been a great barrier to a realization of a fully integrated design. To solve this problem, miniaturization of passive components is one of the big issues at the present time. This paper shows the development of two important microwave passive components, quadrature hybrid and rat-race couplers for LTE lower (698 -960 MHz) and higher (1.71 - 2.70 GHz) frequency bands, which are obtained by replacing quarter-wave (λ/4) transmission line of a conventional coupler by their equivalent coupled line, resulting in significant size reduction. The miniaturized quadrature and rat race couplers are designed and fabricated with a Rogers 4360 substrate as a platform in producing significantly reduction. The design is validated by electromagnetic simulation and measurement. The size of the implemented quadrature hybrid coupler is 30 × 26.8 mm^2 and 14.9 × 12.5 mm^2, which are 82.60 % and 69.03% compared to the conventional couplers for lower and higher frequency band respectively. And, 55.5 × 27.9 mm^2 and 19.2 × 14.8 mm^2 for rat race coupler, which are 79.69 % and 62.35 % compared to the conventional coupler for lower and higher frequency band, respectively. Also, the reflection coefficient and the isolation are as good as conventional one and coupling procedure is similar or better than it.

No description available.