Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

A wideband microwave balun is designed to adapt unbalanced to balanced transmission line networks. The balun is realized by a planar microstrip line configuration on a double copper c1added teflon-ceramic C0I11posite board. The microstrip line conductor pattern was formed on the board using the chemical etching process. The fabricated balun is measured and evaluated in both the time domain and frequency domain, indicating a 5 GHz bandwidth. The time domain modeling technique is used to characterize the balun's performance. Based on physical analysis of the balun's configuration, the discontinuities through the transmission paths are modeled as distributed and lumped elements, resulting in an equivalent network model for the balun structure. The obtained model successfully simulates the balun's performance. / Master of Science

This dissertation reflects the results of probably the very first attempt to cure sol gel ceramers using microwaves. These materials were first prepared in 1985, but were found to take almost two to six days to cure, when stored under ambient conditions. Microwaves have been found to provide a method for circumventing this problem under certain conditions. It was discovered that the more highly phase separated ceramer systems can be cured in twenty minutes when subjected to heating in a microwave field. Curing in a conventional oven, has on the other hand been found to hinder the extent of reaction because the slow initial rate of heating (which allows for evaporation of some of the compatibilizing solvent media) is believed to leave the reactants in a somewhat diffusion limited state. Dielectric investigations on the ceramer films show the existance of Maxwell Wagner Sillars intefacial polarization which results from charge migration in the ceramer system and also show the possibility of PTMO chain expansion at higher metal alkoxide contents in these ceramers when cast onto a substrate onto which the film adheres. Finally, structural investigations into the ceramers using SAXS, gives an idea of the fractal dimensions of the scattering phases. These investigations have also proved quite conclusively that there exists a contribution to scattering from the porosity present in the inorganic phase at metal alkoxide contents as low as 40 wt%. / Ph. D.

For size miniaturization and cost reduction, the design of dual band devices has become an emerging research area in recent years. A desirable dual-band solution should offer size compactness, high performance (e.g. low insertion loss) and compatible with conventional printed circuit broad (PCB) technology, especially microstrip lines. / In this research, several new devices, including rat-race coupler, power divider and crossover junction, capable of operating at dual frequency bands are proposed. These structures involve only simple branch-line sections and a minimal number of shunt stubs. All characteristic impedances are ranged from 20 O to 100 O. Most designs can operate with wide frequency spacing between the two bands. These designs offer low insertion loss as well as good return loss performances, and are small in size, in compared to the broadband approach. For design purposes, explicit closed-form equations are derived for the evaluation of circuit parameters. In addition, the usable range of these devices with respect to frequency band separation is examined. For verification, various prototypes are constructed by using microstrip technology and in-house fabrication facilities. Both simulated and measured results are presented and compared with state-of-the-art examples. / Microwave passive couplers are widely used in microwave and millimeter-wave applications and communication systems. Common examples are branch line coupler, rat race coupler, power divider, and crossover junction. They are used for the dividing, combining and re-directing of signal power. / Very often, a passive coupler utilizes simple quarter-wavelength transmission lines for implementation which will lead to narrow-band operation. Therefore, it is difficult to deploy such circuit for wide-band or multi-band applications. Multi-section topologies may be used to broaden the operating bandwidth, with which the major drawbacks are enlarged circuit size and the requirement of extreme high (or low) branch-line characteristic impedances. Both are not attractive for mass and low cost production. Conventional design approaches are, therefore, not suitable for modern communication systems with multi-band operation. / Wong, Fai Leung. / Adviser: Michael Cheng. / Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 118-122). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

In the analysis of optically controlled microstrip interdigitated gaps, an equivalent circuit model for simple interdigitated gap is obtained. As far as we know, this is the first report of optically controlled microstrip interdigitated gap equivalent circuit model. The amplitude and phase changes of interdigitated gaps under different illumination powers are calculated with this equivalent circuit model, which basically agree with the experimental results. Meanwhile, the effect on the transmission characteristics from the gap dimensions is also discussed. Finally a novel gap structure is described for optically controlled phase shifter application, whose transmission characteristics have nearly zero amplitude change and no less than 27 degrees phase change under different illumination powers when the transmission signal frequency is about 1.8 to 2.5GHz. Some detailed experimental results of this gap are presented in Chapter 5. / In this dissertation, a systematic work has been done to analyze the transmission characteristics and applications of optically controlled microstrip single gap and interdigitated gap devices on high resistivity silicon (HRS) wafer. Detailed simulations, experiments and the relative equivalent circuit models for these gap structures are presented. / Microwave photonics is a multi-disciplinary area that studies the interactions between microwave signals and optical signals. As one of the key elements, direct optical control of microwave semiconductor devices has been an area of growing interest since 1980's. They can be widely used in picosecond photoconductive switch, phase shifter, attenuator, high-speed sampling, gain control of amplifier and so on. / Some future work is also suggested based on the study in this dissertation. / Specifically, optically controlled microstrip discontinuities devices fabricated on semiconductor substrates have wide-ranging applications due to their simple fabrication, easy integration with other passive and active microwave devices. / When illuminated on the surface of the microstrip single gaps, the S 12 amplitude of this gap increases linearly as the optical illumination increasing, which is a good potential application for digital controllable attenuator. The change of the S12 amplitude is mainly due to the imaginary permittivity change of the HRS substrates. The equivalent circuit model is established to explain the amplitude and phase changed. The equivalent resistors have been calculated according to the excess carrier concentration profile after illumination, which match well with the experimental results. / Li Huiping. / "March 2005." / Adviser: K. T. Chan. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6619. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

在現代通信系統，無線服務的需求不斷增加，帶動了通信系統，支持多標準的操作需要。 雙波段或多波段操作幾乎都是必要的，能夠提供這些操作的微波器件已成為減小尺寸和降低成本有吸引力的解決方案。 / 分支線耦合器是用於微波和毫米波應用的最流行的無源電路之一。它們通常用於平衡放大器和混頻器去實現良好的回波損耗以及隔離。其中一個至關重要的部份是設計一個可以靈活作多波段分配的分支線耦合器。 / 傳統上，完全平面的實施，雙波段分支線耦合器可以通過短截線，階梯阻抗線，耦合線等不同的分佈式結構實現。不同的設計方案已在這幾年來出現。窄帶操作和複雜的電路設計，是以前的設計的主要缺點。雖然，在理論上，多節技術可以拓寬帶寬，但它的主要缺點是電路的面積變大了及使用極端低/高傳輸線阻抗。因此，它不是一個大量和低成本生產的解決方案。 / 在這項研究中，設計了全新的並增強了性能的雙波段分支線耦合器(零分貝和三分貝的功率分裂)。這些設計能在兩個指定的頻帶有不平等的工作帶寛。通過正確選擇雙頻四分之一波長阻抗變換器的電氣長度和線路阻抗，傳輸相位斜率將能夠被控制並給出帶寬不對稱的特點，其性能可以進一步擴展，涵蓋了廣泛的應用。 / 以上所有設計都只需要單層線路版的制作及可實現的傳輸線阻抗。應用奇/偶模式分析所給出設計公式。這些設計具有低損耗，佈局靈活，緊密的尺寸大小的特性。這些設計己經使用標準微帶的結構實現其特點，其結果得到了實驗結果的進一步驗證。分支線耦合器只需要更小的節數就能實現相同的性能。 / In modern communication systems, the increasing demand for wireless services has driven the need for communication systems that support multi-standard operations. Dual-/Multi- band operation is almost a necessity and the adoption of microwave multi-band devices has become an attractive solution towards size and cost reduction of RF frontend designs. / Branch-line coupler is one of the most popular passive circuits used for microwave and millimeter-wave applications. They are commonly used in balanced amplifiers, phase-shifter, mixer and frequency multipliers for achieving good return loss, as well as isolation. It is therefore essential to have a branch-line coupler with multi-band operation. / Traditionally, for fully planar implementation, the construction of dual-band branch-line couplers are usually accomplished by distributed structures based upon shunt-stub, stepped-impedance line, coupled line etc. Narrow-band operation and circuit complexity are the major drawbacks for these previous designs. Although, in theory, the available bandwidth may be broadened by multi-section configurations, its major tradeoffs are the enlarged circuit size as well as the extreme line dimensions involved. Therefore, it is not preferable to mass and low cost production. / In this research, advanced designs of dual-band branch-line coupler (0 dB and 3 dB power splitting) with enhanced performances are presented. By proper selection of the number of sections, electrical lengths and line impedances of appropriate branch-lines of the coupler, its performance can be further extended to cover a wide range of applications. / All the proposed circuits require only single-layer fabrication and realizable line impedance. Closed form design formulas are made available by the application of even/odd- mode formulation. They feature low loss, flexible layout and compact size. The designs have been implemented and characterized using standard microstrip, and verified experimentally. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Yeung, Sung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 92-95). / Abstracts also in Chinese. / Abstract --- p.ii / 摘要 --- p.iii / Acknowledgement --- p.iv / Table of Content --- p.v / Lists of Figures --- p.viii / Lists of Tables --- p.xii / Chapter Chapter 1 --- : Introduction --- p.1 / Chapter 1.1 --- Research Motivation and Objective --- p.1 / Chapter 1.2 --- Original Contribution --- p.3 / Chapter 1.3 --- Research Approach, Assumptions and Limitations --- p.4 / Chapter 1.4 --- Overview of the Thesis Organization --- p.5 / Chapter Chapter 2 --- : Review of Microwave Coupler Design --- p.6 / Chapter 2.1 --- Coupler Design Fundamental --- p.6 / Chapter 2.1.1 --- Coupler Design with Equal Power Splitting --- p.7 / Chapter 2.1.2 --- Coupler Design with Unequal Power Splitting --- p.12 / Chapter 2.1.3 --- 0-dB Coupler or Crossover --- p.16 / Chapter 2.1.4 --- Coupler Design with Size Miniaturization --- p.18 / Chapter 2.1.5 --- Wide Band Coupler Design --- p.21 / Chapter 2.2 --- Dual-Band and Multi-Band Branch-line Coupler --- p.25 / Chapter 2.2.1 --- Dual-Band Couplers Based on Composite Right/Left-Handed Transmission Line --- p.25 / Chapter 2.2.2 --- Dual-Band Couplers with Shunt Stubs --- p.28 / Chapter 2.2.3 --- Dual-Band Coupler Based on Stepped-Impedance-Stub-Line --- p.30 / Chapter 2.2.4 --- Dual-Band Coupler with Port Extensions --- p.33 / Chapter 2.2.5 --- Tri-Band Coupler Based on Matching Network --- p.35 / Chapter 2.2.6 --- Multi-passband Branch-line Coupler Design --- p.37 / Chapter 2.3 --- Summary --- p.39 / Chapter Chapter 3 --- : A Novel Dual-band 0-dB Branch-line Coupler Design --- p.40 / Chapter 3.1 --- Proposed Circuit --- p.40 / Chapter 3.2 --- Analysis of Single-band 0-dB Branch-line Coupler --- p.43 / Chapter 3.3 --- Single- to Dual-band Conversion --- p.52 / Chapter 3.4 --- Experimental Results --- p.55 / Chapter 3.5 --- Summary --- p.58 / Chapter Chapter 4 --- : A Novel Dual-band 3-dB Branch-line Coupler with Unequal Bandwidth --- p.59 / Chapter 4.1 --- Proposed Dual-band Impedance Transformer: --- p.59 / Chapter 4.2 --- Single-band 3-dB Coupler Design --- p.65 / Chapter 4.3 --- Dual-band 3-dB Coupler Design --- p.70 / Chapter 4.4 --- Experimental Results --- p.76 / Chapter 4.4.1 --- Equal bandwidth design --- p.76 / Chapter 4.4.2 --- Unequal bandwidth design --- p.78 / Chapter 4.5 --- Summary --- p.81 / Chapter Chapter 5 --- : A Novel Dual-band 0-dB Branch-line Coupler Design with Unequal Bandwidth --- p.82 / Chapter 5.1 --- Proposed Circuit --- p.82 / Chapter 5.2 --- Analysis and Formulation --- p.84 / Chapter 5.3 --- Simulation Results --- p.85 / Chapter 5.4 --- Experimental Results --- p.87 / Chapter 5.5 --- Summary --- p.89 / Chapter Chapter 6 --- : Conclusion and Recommendation for Future Work --- p.90 / Chapter 6.1 --- Conclusion --- p.90 / Chapter 6.2 --- Recommendation for future work --- p.91 / References --- p.92 / Author’s Publications --- p.96 / Chapter Appendix 1: --- Brief Summary of Design Approaches of Hybrids Couplers --- p.97 / Chapter Appendix 2: --- Transformation between S- and ABCD- parameters for two-port network --- p.99

Graduate

Not available / text

Though declining in popularity over the last decade, the magnetron still has applications where portable high power is needed. This study examines the predicted performance of cylindrical microwave magnetrons using analytic lumped-spoke models based on the energy conservation principle. The analytic approach is still favoured when small computer systems are used and the overall performance of the tube is to be predicted. The magnetron elements are examined and the role they play in the overall device performance analysed. Simplified representations of these elements are used to construct a complete magnetron model. The Hartree threshold condition is reexamined and a new, more accurate analytic formulation proposed. This formulation is based on electric field strengths at the base of the magnetron spoke. The effect of the space charge on the threshold condition is included. Spoke current has been evaluated at the edge of the Brillouin hub. The resulting anode- cathode voltage performance predictions are consistent with measured results. A computer program has been written to analyse the performance predicted by this model. Models proposed by other authors are examined, and compared to this model. The resulting model has been tested by comparing predicted results to the measured performance of four slot-and-hole magnetrons. To facilitate accurate magnetron testing, a new automated triple-stub high power microwave load has been developed. The load operates at a peak power of IMW from 2,7-3,OGHZ, and allows the change of the VSWR to any value along any path within the VSWR=I, 5: I circle. The development of the triple tuner and termination is discussed in detail. A new waterload configuration which has the advantage of simple construction yet good matching characteristics is presented. Automated measurement of pulling figure and construction of Rieke diagrams is discussed. The accuracy of the complete load is compared to conventional loads currently in service in the tube industry. / Thesis (Ph.D.)-University of Natal, Durban, 1988.

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