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 (PhD (Electric and Electronic Engineering))--University of Stellenbosch, 2005. / A tunable X-band PIN diode switch, implemented in evanescent mode waveguide, is presented. To allow in-situ tuning of resonances after construction, a novel PIN diode mounting structure is proposed and verified, offering substantial advantages in assembly costs. Accurate and time-effective modelling of filter and limiter states of the proposed switch is possible, using an evanescent mode PIN diode and mount model. The model is developed by optimizing an AWR Microwave Office model of a first order switch prototype with embedded PIN diode, to simultaneously fit filter and limiter measurements of four first order prototypes. The model is then used in the design of a third order switch prototype, achieving isolation of 62 dB over a 8.5 to 10.5 GHz bandwidth in the limiting state, as well as reflection of 15.73 dB and insertion loss of 1.23±0.155 dB in the filtering state over the same bandwidth.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / Due to a more densely packed frequency spectrum, there is an increasing demand for narrow band filters with asymmetrical transfer function characteristics. The resulting coupling matrices contain both positive and negative couplings, cross couplings and individual resonator frequency offsets.

The need for miniaturized, and high performance microwave devices has focused significant attention onto new fabrication technologies that can simultaneously achieve high performance and low manufacturing complexity. Additive manufacturing (AM) has proven its capability in fabricating high performance, compact and light weight microwave circuits and antennas, as well as the ability to achieve designs that are complicated to fabricate using other manufacturing approaches. Direct print additive manufacturing (DPAM) is an emerging AM process that combines the fused deposition modeling (FDM) of thermoplastics with micro-dispensing of conductive and insulating pastes. DPAM has the potential to jointly combine high performance and low manufacturing complexity, along with the possibility of real-time tuning. This dissertation aims to leverage the powerful capabilities of DPAM to come-up with new designs and solutions that meet the requirements of rapidly evolving wireless systems and applications. Furthermore, the work in this dissertation provides new techniques and approaches to alleviate the drawbacks and limitations of DPAM fabrication technology. Firstly, the development of 3D packaged antenna, and antenna array are presented along with an analysis of the inherent roughness of 3D printed structures to provide a deeper understanding of the antenna RF performance. The single element presents a new volumetric approach to realizing a 3D half-wave dipole in a packaged format, where it provides the ability to keep a signal distribution network in close proximity to the ground plane, facilitating the implementation of ground connections (e.g. for an active device), mitigating potential surface wave losses, as well as achieving a modest (10.6%) length reduction. In addition, a new approach of implementing conformal antennas using DPAM is presented by printing thin and flexible substrate that can be adhered to 3D structures to facilitate the fabrication and reduce the surface roughness. The array design leverages direct digital manufacturing (DDM) technology to realize a shaped substrate structure that is used to control the array beamwidth. The non-planar substrate allows the element spacing to be changed without affecting the length of the feed network or the distance to the underlying ground plane. The second part describes the first high-Q capacitively-loaded cavity resonator and filter that is compatible with direct print additive manufacturing. The presented design is a compromise between quality factor, cost and manufacturing complexity and to the best of our knowledge is the highest Q-factor resonator demonstrated to date using DPAM compatible materials and processes. The final version of the single resonator achieves a measured unloaded quality factor of 200-325 over the frequency range from 2.0 to 6.5 GHz. The two pole filter is designed using a coupled-resonator approach to operate at 2.44 GHz with 1.9% fractional bandwidth. The presented design approach simplifies evanescent-mode filter fabrication, eliminating the need for micromachining and vias, and achieving a total weight of 1.97 g. The design is fabricated to provide a proof-of-principle for the high-Q resonator and filter that compromises between performance, cost, size, and complexity. A stacked version of the two-pole filter is presented to provide a novel design for multi-layer embedded applications. The fabrication is performed using an nScrypt Tabletop 3Dn printer. Acrylonitrile Butadiene Styrene (ABS) (relative permittivity of 2.7 and loss tangent of 0.008) is deposited using fused deposition modeling to form the antenna, array, resonator, and filter structures, and Dupont CB028 silver paste is used to form the conductive traces conductive regions (the paste is dried at 90 °C for 60 minutes, achieving a bulk DC conductivity of 1.5×106 S/m.). A 1064 nm pulsed picosecond Nd:YAG laser is used to laser machine the resonator and filter input and output feedlines.

<div>The allocated frequency bands for the incoming fifth generation (5G) wireless communication technologies spread broadly from sub 6 GHz to K and potentially W bands. The evolution of the future generations toward higher frequency bands will continue and presents significant challenges in terms of excessive system complexity, production and maintenance costs. Reconfigurable radio architecture with frequency-tunable components is one of the most feasible and cost-effective solutions to meet such challenges. Among these technologies, evanescent-mode (EVA) cavity tunable resonator have demonstrated many of the needed features such as wide tunability, low loss and high linearity. Such a technology typically employs a movable membrane that controls the resonant frequency of a post-loaded cavity. </div><div><br></div><div>The first part of this work focuses on advancing such technology into the mm-wave frequency bands and beyond. Manufacturing tolerance and tuner performance are the two main limiting factors addressed here. This work develops a cost-effective micro-fabrication and package assembly flow which addresses the manufacturing related limitations. On the other hand, introducing micro-corrugated diaphragms and gold-vanadium co-sputtered thin film deposition technology, significantly reduces (4 times) the tuning voltage and enhances tuning stability (7 times). We demonstrate a tunable two-pole band-pass filter (BPF) prototype as the first EVA cavity tunable filter operating in the K-Ka band. </div><div><br></div><div>The second part of this work extensively discusses an optimal RF design flow based on the developed manufacturing technology. It considers all technology constrains and allows the actualization of a high Q transfer function with minimum bandwidth variation within an octave tuning range. Moreover, a new fully passive input/output feeding mechanism that facilitates impedance matching over the entire tuning range is presented. The devised RF methodology is validated through the design and testing of a two-resonator BPF. Measurements demonstrate a tuning range between 20-40 GHz, relative bandwidth of 1.9%-4.7%, and impedance matching over the entire tuning range which is upto 2 times better than previously reported state-of-the-art MEMS tunable filters of this type.</div><div><br></div><div>The third part of this work further advances the technology by proposing the first MEMS-based low-power bi-directional EVA tuning approach that employs both the main bias circuitry as well as a new corrective biasing technique that counteracts viscoelastic memory effects. The two key enabling technologies are extensively discussed: a) a new metal-oxide-metal (MOM) sealed cavity that maintains high quality without requiring complicated metal bonding; and b) a new electrostatic bi-directional MEMS tuner that implements the needed frequency tuning without lowering the resonator quality factor. </div><div><br></div><div>Furthermore, we explore important design and fabrication trade-offs regarding sensitivity to non-ideal effects (residual stress, fabrication imperfections). Measurement of the new prototype bi-directional design, prove that this technology readily corrects residual post-bias displacement of 0.1 um that shifts the frequency by over 1 GHz with less than 2.5 V. It takes over 100 seconds to recover this error in the uni-directional case. This correction does not adversely affect the filter performance.</div>