Recently, there have been a great interest in the millimeter-wave (mmW) and terahertz (THz) bands due to the unique features they provide for various applications. For example, the mmW is not significantly affected by the atmospheric constraints and it can penetrate through clothing and other dielectric materials. Therefore, it is suitable for a vast range of imaging applications such as vision, safety, health, environmental studies, security and non-destructive testing. Millimeter-wave imaging systems have been conventionally used for high end applications implementing sophisticated and expensive technologies. Recent advancements in the silicon integrated and low loss material passive technologies have created a great opportunity to study the feasibility of low cost mmW imaging systems. However, there are several challenges to be addressed first. Examples are modeling of active and passive devices and their low performance, highly attenuated channel and poor signal to noise ratio in the mmW. The main objective of this thesis is to investigate and develop new technologies enabling cost-effective implementation of mmW and sub-mmW imaging systems. To achieve this goal, an integrated active Rotman lens architecture is proposed as an ultimate solution to combine the unique properties of a Rotman lens with the superiority of CMOS technology for fabrication of cost effective integrated mmW systems. However, due to the limited sensitivity of on-chip detectors in the mmW, a large number of high gain, wide-band and miniaturized mmW Low Noise Amplifiers (LNA) are required to implement the proposed integrated Rotman lens architecture. A unique solution presented in this thesis is the novel Band Pass Distributed Amplifier (BPDA) topology. In this new topology, by short circuiting the line terminations in a Conventional Distributed Amplifier (CDA), standing waves are created in its artificial transmission lines. Conventionally, standing waves are strongly avoided by carefully matching these lines to 50 ?? in order to prevent instability of the amplifier. This causes that a large portion of the signal be absorbed in these resistive terminations. In this thesis, it is shown that due to presence of highly lossy parasitics of CMOS transistor at the mmW the amplifier stability is inherently achieved. Moreover, by eliminating these lossy and noise terminations in the CDA, the amplifier gain is boosted and its noise figure is reduced. In addition, a considerable decrease in the number of elements enables low power realization of many amplifiers in a small chip area. Using the lumped element model of the transistor, the transfer function of a single stage BPDAs is derived and compared to its conventional counter part. A methodology to design a single stage BPDA to achieve all the design goals is presented. Using the presented design guidelines, amplifiers for different mmW frequencies have been designed, fabricated and tested. Using only 4 transistors, a 60 GHz amplifier is fabricated on a very small chip area of 0.105 mm2 by a low-cost 130 nm CMOS technology. A peak gain of 14.7 dB and a noise figure of 6 dB are measured for this fabricated amplifier. oreover, it is shown that by further circuit optimization, high gain amplification can be realized at frequencies above the cut-off frequency of the transistor. Simulations show 32 and 28 dB gain can be obtained by implementing only 6 transistors using this CMOS technology at 60 and 77 GHz. A 4-stage 85 GHz amplifier is also designed and fabricated and a measured gain of 10 dB at 82 GHz is achieved with a 3 dB bandwidth of 11 GHz from 80 to 91 GHz. A good agreement between the simulated and measured results verifies the accuracy of the design procedure. In addition, a multi-stage wide-band BPDA has been designed to show the ability of the proposed topology for design of wide band mmW amplifiers using the CMOS technology. Simulated gain of 20.5 dB with a considerable 3 dB bandwidth of 38 GHz from 30 to 68 GHz is achieved while the noise figure is less than 6 dB in the whole bandwidth. An amplifier figure of merit is defined in terms of gain, noise figure, chip area, band width and power consumption. The results are compared to those of the state of the art to demonstrate the advantages of the proposed circuit topology and presented design techniques. Finally, a Rotman lens is designed and optimized by choosing a very small Focal Lens Ratio (FL), and a high measured efficiency of greater than 30% is achieved while the lens dimensions are less than 6 mm. The lens is designed and implemented using a low cost Alumina substrate and conventional microstrip lines to ease its integration with the active parts of the system.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This project comprises the design, analysis, and construction of a Rotman lens with reduced conjugate-port coupling. The Rotman lens is a beam-forming network, used in wide-angle scanners to feed an antenna array. The scanning operation is based on optics and is therefore frequency invariant, a desirable feature of the Rotman lens compared to other beam-forming networks which employ phase shifters. The antenna array is connected to the lens's array ports via transmission lines. These array ports lie on the array contour which is designed so that a signal incident onto the antenna array will propagate into the lens and focus at a particular point. The position of this focal point depends on the signals direction of arrival at the array. Ports are placed on these focal points to feed and receive signals. Bootlace lenses allow up to four focal points for linear arrays whereas the Rotman lens is designed for three foci. Scanners usually require to scan many beam-widths, thus ports are employed along a focal arc which intersect these foci. Inter-focal ports do not focus perfectly and result in phase errors distributed across the array aperture. The derivation of three and four foci lenses is provided. There are several degrees of freedom at the designer's disposal, the e ect which these available parameters have on the lens geometry and phase errors is investigated. The waveguide implementa- tion of these lenses is examined, in which we use vertically polarised horns as feed ports and coaxial probes as array ports. Some designs of Rotman lenses published in literature show excess mutual cou- pling between symmetrically opposed feed ports. Using a model which approximates the array contour as a re ecting wall, we show that this is due to the re ected energy focusing on conjugate ports. It is identi ed that Rotman lenses designed for mini- mum phase errors will have near maximum conjugate-port coupling. Two Rotman lenses have been designed at 3; 5GHz for ve feed ports, eleven elements, and up to 30 scan angles. The rst is designed for minimum phase errors, and the second for the defocusing of the re ected energy from the focal arc. Simulations show up to a 10dB reduction in conjugate-port coupling for the second lens with a negligible degradation in performance from the phase errors. Measurements show that the re ected energy is spread between the feed ports as expected, compared to the focusing at a single port of the traditional Rotman lens. / AFRIKAANSE OPSOMMING: Hierdie projek behels die ontwerp, analise en konstruksie van 'n Rotmanlens met verminderde simmetries oorstaande poort koppeling. Die Rotmanlens is 'n patroon- vormingsnetwerk wat gebruik word as samestellingvoer in wye hoek skandeerders. 'n Gewensde eienskap van die Rotmanlens bo faseskuif voernetwerke is dat die skan- deerwerking gebasseer is op optika en dus frekwensie onafhanklik is. Die antennasamestelling word deur transmissielyne verbind aan die antennapoorte van die lens. Hierdie poorte l^e op die samestellingkontoer wat ontwerp is om te verseker dat seine wat inval op die antennasamestelling sal voortplant in die lens en fokus op 'n spesi eke punt. Die posisie van die fokuspunt hang af van die invalshoek van die sein op die samestelling. Poorte word op hierdie fokuspunte geplaas om te seine te ontvang en te lanseer. Hierdie tipe lense kan tot vier fokuspunte h^e , waar die Rotman lens spesi ek vir drie fokuspunte ontwerp word. Skandeerders moet normaalweg etlike bundelwydtes wyd kan skandeer, en daarom word poorte geplaas op 'n straal wat die fokuspunte onderskep. Poorte wat weg van die fokus geplaas word toon 'n e ens uit fokus gedrag, wat vertaal na fasefoute in die samestelling stralingsvlak. Die a eiding van drie en vier fokus lense word verskaf. Daar is verskeie grade van vryheid tot die beskikking van die ontwerper, en die e ek wat die beskikbare parameters op die geometrie van die lens en die fase foute het word ondersoek. Die gol eier implimetering van hierdie lense word beskryf, waar vertikaal gepolariseerde horings as voerpoorte, en ko-aksiale lyne as antennapoorte gebruik word. Sommige Rotman lens ontwerpe in die literatuur toon beduidende koppeling tussen die simmetries oorstaande voerpoorte. Deur van 'n model gebruik te maak wat die samestellingkontoer as 'n weerkaatsende muur benader toon ons aan dat die koppeling geskied as gevolg van die weerkaatsde energie wat fokus in die simme- tries oorstaande poorte. Dit word identi seer dat Rotman lense wat vir minimum fasefoute ontwerp word bykans maksimum koppeling tussen simmetries oorstaande poorte tot gevolg het. Twee Rotman lense is ontwerp by 3; 5GHz vir vyf voerpoorte, elf antenna ele- mente en skandeer hoeke van 30. Die eerste is ontwerp vir minimum fasefoute en die tweede vir uit fokus weerkaatsde energie vanuit die fokus straal. Simulasies toon tot 10 dB vermindering in koppeling tussen simmetries oorstaande poorte vir die tweede lens met weglaatbare werkverrigting verswakking as gevolg van fasefoute. Metings toon dat die weerkaatsde energie, soos verwag, versprei word tussen die voerpoorte vergeleke met energie gefokus in 'n enkele poort soos by die tradisionele Rotman lens.

Microwave lenses support low-phase error, wideband, wide-angle scanning, and true-time delay (TTD) beam forming. They provide ideal performance for applications such as satellites, remote-piloted vehicles, collision-avoidance radars and ultra-wideband communications systems. The emerging printed lenses in recent years have facilitated the advancement of designing high performance but low-profile, light-weight, and small-size beam-forming networks (BFNs). The microwave lens adopts a few beam ports to illuminate the prescribed receiving ports that feed energy into radiating antennas. Multi-beam patterns can be achieved by exciting multiple beam ports at a time. The design process starts with path-length equations from a limited number of beam-port foci assumptions. This constraint does not take into account the amplitude information; however, it allows an initial lens geometry to be solved. The resulted scanning angle of microwave lens is limited by the beam port contour, as such ± 90 degrees. In this dissertation, three contributions are made from the aspects of minimized phase errors, accurate and efficient simulation algorithms, and 360-degree scanning range extension. First, a minimum-phase-error, non-focal lens design method is proposed. It does not require a specific number of foci along the beam contour; however, minimum phase errors for all beam ports are able to be achieved. The proposed method takes into account flexible prescribed geometrical design parameters, and adopts numerical optimization algorithms to perform phase error minimization. Numerical results compared with the published tri-focal and quadru-focal lenses demonstrate the merits of the proposed method. Second, an accurate and fast simulation method for the microwave lens has been developed to predict the phase, amplitude, array factor, and power efficiency performance. The proposed method is compared to both full-wave simulation and measurement. Comparable results have been achieved. Third, a novel method for a 360-degree scanning microwave lens is proposed. This concept uses the beam ports and the receive ports in an interleaving sequence such that adjacent ports alternate beam and receive functions. The result is a lens that produces scanned beams on opposite sides of the structure resulting in a 360-degree scanning range. The structure can use multiple opposing facets or continuous circular-port and radiating-element contours. To prove the concept, a four-facet microstrip lens has been designed, simulated, fabricated, and tested. The comparison between full-wave simulation and measurement has demonstrated good agreement. / Ph. D.

Les travaux de cette thèse portent sur la conception d'antennes multi-faisceaux. Ces dernières permettent à plusieurs faisceaux de partager la même partie rayonnante et offrent la possibilité d'avoir simultanément un fort gain et une grande couverture angulaire. Pour leur fonctionnement, ces antennes se basent sur des réseaux à formation de faisceaux, qui peuvent être groupés en deux catégories : les réseaux formateurs de faisceaux de type quasi-optique et les réseaux formateurs de faisceaux de type circuit. Plusieurs structures antennaires reposant sur ces types de réseaux à formation de faisceaux sont proposés dans cette thèse : structures pillbox simples intégrant les deux variantes de la technique mono-pulse pour augmenter la résolution angulaire de l'antenne, lentilles de Rotman bicouche et multicouche, pour le cas quasi-optique ; réseaux phasés pour applications SATCOM (projet ANR) et matrice de Butler avec circuit de contrôle des niveaux de lobes secondaires pour le cas circuit. Les différents concepts ont été étudiés dans différentes bandes de fréquences : Ku, K et V. Pour des raisons de coût essentiellement, deux technologies ont été retenues : La technologie SIW (Substrate Integrated Waveguide), qui associe les avantages de la technologie des circuits imprimés et celles de la technologie guide d'ondes. Des efforts particuliers ont été faits pour l'implémentation de structures multicouches car nous arrivons à ce stade à la limite du savoir faire industriel national dans ce domaine. La technique de « Diffusion Bounding » développée au « Ando and Hirokawa lab » du TIT (Tokyo Institute of Technology) et qui consiste à assembler de fines couches métalliques sous haute température et haute pression. Cette technique permet le développement d'antennes en guides creux avec des efficacités supérieures à 80% en bande millimétrique. / This PhD thesis deals with the design of multi-beam antennas. A single radiating aperture is used to generate several beams with high gain and a large field of view. The multi beam operation is achieved by using two topologies of Beam Forming Networks (BFN): quasi optical BFN, and circuit-based BFN. For each category, several solutions have been proposed and validated experimentally. In particular, for the quasi-optical configurations, pillbox structures, mono-pulse antennas in pillbox technology, and multi-layer Rotman lenses have been considered. On the other hand, for circuit-based multi-beam antennas, two solutions have been analyzed: a phased array for SATCOM applications in the framework of a national ANR project and a Butler matrix with controlled side-lobe levels for the radiated beams within a collaboration with the Tokyo Institute of Technology, Japan. The proposed concepts and antenna solutions have been considered in different frequency bands: Ku, K and V. Two technologies have been mainly adopted for the fabrication of the various prototypes: Substrate Integrated Waveguide technology (SIW) which combines the advantages in terms of cost of the printed circuit board (PCB) fabrication process with the efficiency of classical waveguide technology. Considerable efforts have been devoted to the implementation of multilayer SIW structures to overcome and go beyond the current state of the art at national level on PCB fabrication process. Diffusion Bounding Technique, developed at “Ando and Hirokawa lab” at the Tokyo Institute of Technology, which consists of bonding laminated thin metal plates under high temperature and high pressure. This technique allows the fabrication of planar hollow waveguide structures with efficiencies up to 80% in the millimeter wave-band.