Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: An investigation of the functional similarities and di erences between a combline lter and an evanescent-mode waveguide lter is presented. The design theory of the two types of lters is outlined. Two lters are designed to operate at a centre frequency of 2 GHz with a 5% bandwidth using similar waveguide dimensions, but using the two di erent design theories. The bandpass characteristics of the two lters are then compared over the primary passband and over a broad range of frequencies to observe the stopband characteristics. It is shown that a combline lter with a large groundplane spacing behaves like an evanescent-mode waveguide lter but a di erence in bandwidth exists between the two. Di erent aspects related to the manufacture of coaxial cavity lters are addressed with speci c emphasis on cost reduction. The considerations to be made when choosing the right materials, manufacturing techniques and surface nishes for microwave coaxial cavity lters so that good performance is obtained while reducing the overall costs associated with manufacturing are discussed. The concept of Design for Manufacture (DFM) is discussed. Three combline lters are designed for reduced manufacturing cost, applying di erent changes in the physical structure to suit the speci c manufacturing technique used. Two of these have the same design speci cations, operating at a centre frequency of 1.3 GHz with a 10% bandwidth but are designed for manufacture using two di erent manufacturing techniques: milling and wire-cutting EDM. The third lter is designed for manufacture using a combination of the milling and wirecutting processes to have a bandwidth of 1.8% with the primary passband centred at 2.125 GHz. Problems encountered in manufacturing are explained, one of which results in the use of waterjet cutting for the manufacture of lters initially supposed to be manufactured using wirecutting EDM. Measurement results for the manufactured lters show a good agreement between the bandwidths of the 3D electomagnetic simulation results. The obtained results also show the e ects of poor surface nishing and of deformations on the resonant frequency and the unloaded Q of the lters. / AFRIKAANSE OPSOMMING: 'n Studie van die funksionele ooreenkomste en verskille tussen kamlyn lters en gol eier-onder-afknip lters word aangebied. Die ontwerpstegnieke van beide tipes lters word aangebied. Twee lters word ontwerp met 'n senterfrekwensie van 2GHz en 'n bandwydte van 5%, met soortgelyke gol eierafmetings maar deur gebruik te maak van die verskillende ontwerpstegnieke. Die gedrag van die twee lters word vergelyk in die deurlaatband sowel as oor 'n wye stopband. Dit word getoon dat 'n kamlyn lter met 'n groot grondvlakspasi ering soos 'n gol eier-onder-afknip lter optree, met 'n verskil in bandwydte. Verskillende aspekte wat verband hou met die vervaardiging van koaksiale lters, met spesi eke klem op koste vermindering, word aangebied. Die oorwegings wat die keuses van materiaal, vervaardigingstegnieke en oppervlakte afwerking be nvloed word bespreek. Die konsep van Ontwerp vir Vervaardiging (DFM in Engels) word bespreek. Drie kamlyn lters word ontwerp vir verminderde vervaardigingskoste deur die siese sruktuur aan te pas by die spesi eke vervaardigingstegniek. Twee van die lters het dieselfde spesi kasie, naamlik 'n senterfrekwensie van 1.3GHz en 'n 10% bandwydte, maar word ontwerp vir twee verskillende vervaardigingsprosesse, naamlik frees en draadsny. 'n Derde lter word ontwerp vir 'n kombinasie van hierdie twee prosesse, en met 'n senterfrekwensie van 2.125GHz en 'n bandwydte van 1.8%. Probleme met die vervaardiging word bespreek, onder andere die verandering van draadsny na water-sny tegnieke. Gemete resultate toon goeie ooreenstemming met die teoretiese analise wat die bandwydtes betref, maar swak oppervlak afwerking het 'n verswakking van die onbelaste Q van die resoneerders tot gevolg.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The purpose of this project is to develop a number of coaxial resonator lters. Firstly, the theoretical model of the lter is discussed, with a Tchebyscheff LC-ladder prototype lter used to derive a generalised bandpass lter. From this, generalised Combline- and Interdigital lters are derived. Following this, various options and limitations in the mechanics of microwave lters are discussed. Results are shown for an in-depth study considering the unloaded quality factor for thirteen di erent resonators. Each resonator is unique in the method of manufacturing, polishing, as well as plating. Utilizing the information obtained from the unloaded quality factor measurements, three coupled coaxial resonator lters, are designed for use in a radar system, namely a sixth order 2125 MHz Combline lter, a sixth order 9250 MHz Interdigital lter and a third order 9250 MHz Interdigital lter. Optimal results were obtained when both resonators and coupled transmission line lters were constructed from aluminium that was wire-cut and then silver electroplated. / AFRIKAANSE OPSOMMING: Die omvang van hierdie projek behels die ontwerp en bou van ko-aksiale resoneerder filters. Eerstens word die teoretiese modellering van die lters bespreek. 'n Tchebyscheff LC-leer prototipe filter word gebruik as basis vir 'n generiese banddeurlaat filter. Die banddeurlaat lter word gebruik om die afgeleide Kamlyn- en Interdigitale filter te de finieer. Hierna volg 'n bespreking aangaande die verskillende moontlikhede in die meganiese vervaardiging van mikrogolf filters. 'n Gedetailleerde studie word gedoen om die onbelaste kwaliteitsfaktore van 13 verskillende resoneerders te bepaal. Elkeen van hierdie resoneerders is uniek in die metode van vervaardiging, polering, asook die platering daarvan. Deur gebruik te maak van die resultate van die onbelaste kwaliteitsfaktore, word drie gekoppelde ko-aksiale resoneerder filters ontwikkel vir die gebruik in 'n radarstelsel, naamlik 'n sesde-orde 2125 MHz Kamlyn lter, 'n sesde orde 9250 MHz Interdigitale filter, asook 'n derde orde 9250 MHz Interdigitale filter. Die beste resultate was gevind toe beide resoneerders en gekoppelde ko-aksiale resoneerder filters vervaardig is uit aluminium wat gedraadsny en silwer geplateer is.

The growth in the number of wireless devices and applications underscores the need for characterizing and mitigating interference induced problems such as distortion and blocking. A typical interference scenario involves the detection of a small amplitude signal of interest (SOI) in the presence of a large amplitude interfering signal; it is desirable to attenuate the interfering signal while preserving the integrity of SOI and an appropriate dynamic range. If the frequency of the interfering signal varies or is unknown, an adaptive notch function must be applied in order to maintain adequate attenuation. This work explores the performance space of a phase cancellation technique used in implementing the desired notch function for communication systems in the 1-3 GHz frequency range. A system level model constructed with MATLAB and related simulation results assist in building the theoretical foundation for setting performance bounds on the implemented solution and deriving hardware specifications for the RF notch subsystem devices. Simulations and measurements are presented for a Low Noise Amplifer (LNA), voltage variable attenuators, bandpass filters and phase shifters. Ultimately, full system tests provide a measure of merit for this work as well as invaluable lessons learned. The emphasis of this project is the on-wafer LNA measurements, dependence of IC system performance on mismatches and overall system performance tests. Where possible, predictions are plotted alongside measured data. The reasonable match between the two validates system and component models and more than compensates for the painstaking modeling efforts. Most importantly, using the signal to interferer ratio (SIR) as a figure of merit, experimental results demonstrate up to 58 dB of SIR improvement. This number represents a remarkable advancement in interference rejection at RF or microwave frequencies.