THESIS
2007
xx, 167 leaves : ill. ; 30 cm
Abstract
Microwave systems have an enormous impact on modern society. Applications are diverse, from entertainment via satellite television, to civil and military radar systems. In particular, the recent trend of multi-frequency bands and multi-function operations in wireless communication systems along with the explosion in wireless portable devices are imposing more stringent requirements such as size reduction, tunability or reconfigurability enhancement, and multi-band operations for the microwave circuits....[
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Microwave systems have an enormous impact on modern society. Applications are diverse, from entertainment via satellite television, to civil and military radar systems. In particular, the recent trend of multi-frequency bands and multi-function operations in wireless communication systems along with the explosion in wireless portable devices are imposing more stringent requirements such as size reduction, tunability or reconfigurability enhancement, and multi-band operations for the microwave circuits.
In this dissertation, we intend to address the design issues related to microwave passive circuits. Several novel design concepts for meeting the above-described challenges in microwave bandpass filters are presented based on in-depth theoretical analysis and practical implementation. For compact bandpass filters, a microstrip tri-section stepped impedance resonator (SIR) and a CPW (coplanar waveguide) tri-section slow-wave SIR are proposed. Compared with the conventional two-section SIR, the size reduction of the new SIRs can be up to 40 percents. Filters based on the new SIR structures are designed and implemented in low-cost PCB, with excellent agreement between the designed and measured characteristics. To achieve reconfigurability, two types of filters with electronically reconfigurable transmission zeros are proposed using varactor-tapped stubs. In addition, one of these proposed bandpass filters features robust reconfigurability in both the transmission poles (center frequency) and transmission zeros. To achieve multi-band operation, a dual-band quarter-wavelength transmission line is proposed, which can acts as the dual-band impedance inverter. A second-order dual-band filter is constructed based on a dual-band resonator in conjunction with this dual-band impedance inverter. The performance of this filter is verified by measurement results. The proposed dual-band transmission line can be also applied to other microwave passive circuits for dual-band operations. A branch-line coupler, a Wilkinson power divider and two types of rat-race couplers featuring dual-band characteristics are designed and fabricated. The desired dual-band performances are verified by measurement results. The practical issue such as the realizable frequency ratio between the two working frequencies is also discussed.
For theoretical analysis, we have developed a synthesis process based on the genetic algorithm (GA). The direct searching property of the GA obviates the computations of the gradients. To demonstrate the effect of the proposed method, several general Chebyshev filters with different orders and different performances are synthesized. This method is applied to get the prototype design parameters of the filters presented in this dissertation. Besides, the genetic algorithm (GA) is applied to the parameter extraction for the tuning and optimizing of filters. Not much apriori knowledge is required for this method, facilitating an automated computer-aided tuning and optimization platform. To demonstrate the feasibility of our method, filters with both mistuned resonators and mistuned inter-resonator couplings have been studied. For all of these filters, the extracted coupling matrices fit the assigned ones well.
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