<p>Filtri predstavljaju nezaobilazan deo svakog mikrotalasnog uređaja. Skorašnji veoma brz razvoj bežičnih sistema pred mikrotalasne filtre postavlja nove zahteve kao što su visoke performanse, kompaktnost i rad na više proizvoljno odabranih učestanosti koje se mogu nezavisno kontrolisati.<br />Naučni doprinos ove doktorske disertacije predstavlja pet novih konfiguracija mikrotalasnih multi-band filtara koji su realizovani u mikrostrip arhitekturi. Od toga tri konfiguracije predstavljaju dual-band filtre, a preostale dve konfiguracije tri-band filtre. Filtri su realizovani korišćenjem fraktalnih krivih i/ili savijenih &lambda;/4 rezonatora, i to u klasičnoj tehnologiji štampanih ploča i u višeslojnoj tehnologiji nisko-temperaturne zajedno pečene keramike.<br />Detaljno je analiziran i opisan način rada predloženih filtara. Filtri su fabrikovani, a njihove performanse izmerene i upoređene sa drugim rezultatima dostupnim u literaturi. Pokazano je da predložene filtre karakteriše mogućnost nezavisne kontrole propusnih opsega što je iskorišćeno za realizaciju dual-band filtara koji rade na WLAN 2.4/3.5 GHz opsezima i tri-band filtara koji rade na WLAN 2.4/3.5/5.2 GHz opsezima. Štaviše, predložene tri-band strukture predstavljaju najmanje tri-band filtre do danas predložene u literaturi.</p> / <p>Filters are indispensable components in any microwave device. Recent rapid development of wireless systems posed new demands to microwave filters, such as high performance, compact size and the ability to simultaneously operate on several independently selected frequencies.<br />Scientific contribution of this dissertation are five novel microwave multi-band filters realized in microstrip architecture. Out of the five, three configurations are dual-band filters, while the remaining two are tri-band filters. Filters are designed using fractal curves and/or folded &lambda;/4 resonators, in the conventional printed circuits technology or in low-temperature cofired ceramics technology.<br />Operating principles of the proposed filters have been analyzed and explained in detail. Their performances have been measured and compared to other recently published results. It has been shown that the proposed filters allow independent control of the passbands. This has been used to design dual-band filters operating at WLAN frequencies of 2.4/3.5 GHz and tri-band filters operating at WLAN frequencies of 2.4/3.5/5.2 GHz. Moreover, the proposed tri-band filters are the most compact tri-band filters published so far.</p>

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: In this dissertation a number of techniques to design multi-band filters, with specific focus on coupled resonator implementations, is presented. Multi-band transfer functions are constructed from single-band transfer functions using frequency mapping methods. A general class of rational mapping functions is presented that can accommodate arbitrary bandwidth specifications. Multi-band circuits are synthesised directly from multi-band transfer functions and are obtained by applying reactance transformations to single-band prototype circuits. For the direct synthesis of multi-band filters from multi-band transfer functions coupling matrix synthesis methods are employed. The circuits that result from matrix synthesis methods tend to have topologies that are undesirable from a practical perspective and must be simplified using rotations of the coupling matrix. The synthesis of multi-band filters through reactance transformations is both simple and result in filters that have practical topologies for realisation as coupled resonator circuits. Multiple filters are designed using different design methodologies and different transmission line technologies to illustrate the various design possibilities. The designs include both all-pole and cross-coupled filters and employ single-layer stripline, multi-layer stripline as well as coaxial resonators as transmission line technologies for the implementations. / AFRIKAANSE OPSOMMING: In hierdie proefskrif word verskeie ontwerpstegnieke vir multi-band filters aangebied en word daar spesifiek klem gelê op filters wat as gekoppelde resoneerder strukture geïmplimenteer kan word. Multi-band oordragsfunksies word geskep uit enkelband oordragsfunksies deur gebruik te maak van wiskundige afbeeldingstegnieke. ’n Spesiale klas van rasionale funksies word voorgestel wat spesifiek gebruik kan word om multi-band funksies te skep wat ’n arbitrêre bandwydte spesifikasie het. Multi-band stroombane word direk gesintetiseer vanuit multi-band oordragsfunksies en word ook verkry deur die toepassing van reaktansietransformasies op enkelband stroombane. Vir die direkte sintese van multi-band stroombane vanuit multi-band oordragsfunksies word stroombane gesintetiseer as koppelmatrikse. Stroombane wat op hierdie wyse gesintetiseer word is geneig om topologieë te hê wat nie baie gesog is vanuit ’n praktiese perspektief nie en matriks rotasies word dan hier ingespan om die stroombane se topologieë te vereenvoudig. Die sintese van multi-band stroombane deur gebruik te maak van reaktansietransformasies is beide eenvoudig en lei tot stroombane wat praktiese topologieë het vir implimentering as gekoppelde resoneerder strukture. Die ontwerpsmoontlikhede wat die verskillende metodieke bied word geïllustreer deur die ontwerp van verskeie filters op verskillende maniere waar daar gebruik gemaak word van verskeie transmissielyn tegnologië. Die filter ontwerpe sluit filters in waar alle transmissienulle by oneidige frekwensies is, sowel as gevalle waar somige transmissienulle by eindige frekwensies is. Die filters word geïmplimenteer deur gebruik te maak van koaksiale resoneerders sowel as enkellaag en multilaag strooklyn.