Design And Applications Of High-Performance Miniaturized Planar Filters

Filters play important roles in many RF/microwave circuits. Emerging wireless communication applications continue to challenge RF/microwave filters with ever more stringent requirements-higher performance, smaller size, lighter weight, and lower cost. Based on the synthesis of cross-coupled resonator filters, a series of miniaturized planar filters have been proposed. These filters have low insertion loss, high stopband rejection, sharp selectivity, transmission zeros at certain frequencies, and first spurious response far away from the passband. It is believed that these proposed filters will find applications in the compact size and high-performance circuit design.To begin with, the synethesis of cross-coupled resonator filters have been thoroughly studied. A general approach to the synethesis of cross-coupled resonator filters using a hybrid optimization technigue has been proposed and proved by numerical results. A rigorous proof of the maximum number of finite transmission zeros which can be achieved by the fixed topology is presented. The effect of changes in the coupling coefficients and resonant frequencies of the resonators is investigated by direct computing the sensitivity coefficient. A universal synthesis technique of coupled resonator filters with source/load-multiresonator coupling is presented. By letting some selected direct coupling between resonators equal to zero, coupling the source and load to more than one resonator, or introducing more than one main path for the signal between the source and load, a series of new coupling schemes are proposed. Their frequcy characteristics are carefully investigated. To reduce the effects of fabrication tolerance on filter responses and simplify the design procedure, the modular design of quasi-elliptic filters using building blocks is introduced. Each building block is capable of generating one or two finite transmission zeros, and the adjacent blocks are connected by nonresonating nodes (NRN). Using this technique, a modularly designed filter of order N can generate up to N transmission zeros without directly coupling the source to the load. The characteristics of the singlet, doublet, triplet and quadruplet are introduced and these blocks are utilized to build higher order filters.Secondly, the stepped-impedance resonators are investigated, and several innovative filter designs are proposed. The stepped-impedance hairpin resonator and its filter application are presented. By inverting orientation of the resonator and cascading the stepped-impedance hairpin lowpass filters, respectively, filter designs with wider passband and stopband can be realized. Based on a new equivalent circuit model, the miniaturized hairpin resonator has been studied. A four-pole cross-coupled bandpass filter is designed by using these resonators. To improve the stopband rejection, the asymmetric feed structure is proposed. The location of the transmission zeros introduced by the feed structure is studied according to the field distribution. Miniaturized hexagonal stepped-impedance resonators and their applications to bandpass filters are presented. Based on the odd- and even-mode equivalent circuits, the resonance characteristics of these resonators are investigated. A series of filter configurations, including the third-order Chebyshev and trisection bandpass filters, are realized by the proposed resonators. These filters are very compact and have good stopband responses. A novel compact quarter-wavelength resonator filter using the lumped coupling elements is presented. The filter not only has controllable transmission zeros near its passband, but also features compact size and ease of frequency tuning.Thirdly, the dual-mode resonators and bandpass filters are discussed. Novel dual-mode hexagonal loop resonator filters with the patch and notch perturbation are proposed. The field patterns of the dual modes and their mode splitting characteristics are investigated. Different responses can be realized using only a single dual-mode resonator by changing the position of the perturbation. A coupling and routing scheme is presented to model the operations of these filters. Two- and four-pole filters of this type are demonstrated for the first time. Miniaturized dual-mode ring bandpass filters with patterned ground plane are proposed. By loading the resonator periodically with the patterned ground plane on the backside, the size of a ring filter is reduced, along with an extended upper stopband.The final part of this thesis involves a case study of planar filters for a 100 MHz-9.6 GHz frequency multiplier chain applications. The study starts with a brief discussion of the system specifications and spectrums of the frequency multipliers. This is followed by more detailed descripitions of the developments of the filters, including design, fabrication, and tuning. Measued results show that the design meet the specifications well.