Radiation pattern reconfigurable microfabricated planar millimeter-wave antennas

Els serveis de telecomunicacions i sistemes radar estan migrant a freqüències mil•limètriques (MMW), on es disposa d 'una major amplada de banda i conseqüentment d'una major velocitat de transmissió de dades. Aquesta migració requereix de l'ús de diferents tecnologies amb capacitat d'operar a la banda de freqüències mil•limètriques (30 a 300 Ghz), i més concretament en les bandes Ka (26,5 - 40GHz), V (50 – 75GHz) i W (75 – 110GHz). En moltes aplicacions i sobretot en aquelles on l'antena forma part d'un dispositiu mòbil, es cerca poder utilitzar antenes planes, caracteritzades per tenir unes dimensions reduïdes i un baix cost de fabricació. El conjunt de requeriments es pot resumir en obtenir una antena amb capacitat de reconfigurabilitat i amb un baix nivell de pèrdues en cada una de les bandes de freqüència. Per tal d'afrontar aquests reptes, les dimensions de les antenes mil•limètriques, juntament amb els tipus de materials, toleràncies de fabricació i la capacitat de reconfigurabilitat ens porten a l'ús de processos de microfabricació. L'objectiu d'aquesta tesis doctoral és l'anàlisi dels conceptes mencionats, tipus de materials, geometries de línia de transmissió i interruptors, en el context de les freqüències mil•limètriques, així com la seva aplicació final en dissenys d'antenes compatibles amb els processos de microfabricació. Finalment, com a demostració s'han presentat dissenys específics utilitzables en tres aplicacions a freqüències mil•limètriques: Sistemes de Comunicació per Satèl•lit (SCS) a la banda Ka, Xarxes d'àrea personal inalàmbriques (WPAN) a la banda V i sistemes radar per l'automoció a la banda W. La primera part d'aquesta tesis consisteix en l'anàlisi d'algunes tecnologies circuitals a freqüències mil•limètriques. S'han presentat els materials més utilitzats a altes freqüències (Polytetrafluoroethylene or Teflon (PTFE), Quartz, Benzocyclobuten polymer (BCB) i Low Temperature Co-fired Ceramic (LTCC)) i s'han comparat en termes de permitivitat i tangent de pèrdues. També s'inclou un estudi de pèrdues a altes freqüències en les principals línies de transmissió (microstrip, stripline i CPW). Finalment, es presenta un resum dels interruptors RF-MEMS i es comparen amb els PIN diodes i els FET. En la segona part, es presenten diferents agrupacions d'antenes amb la capacitat de reconfigurar la polarització i la direcció d'apuntament. S'han dissenyat dos elements base reconfigurables en polarització: CPW Patch antena i 4-Qdime antena. La primera antena consisteix en un element singular amb interruptors RF-MEMS, dissenyada per operar a les bandes Ka i V. La segona antena consisteix en una arquitectura composta on la reconfigurabilitat en polarització s'obté mitjançant variant la fase d'alimentació de cada un dels quatre elements lineals. La fase és controlada mitjançant interruptors RF-MEMS ubicats en la xarxa de distribució. L'antena 4-Qdime s'ha dissenyat per operar en les bandes V i W. Ambdós elements base s'han utilitzat posteriorment pel disseny de dues agrupacions d'antenes amb capacitat de reconfigurar l'apuntament del feix principal. La reconfigurabilitat es dur a terme utilitzant desfasadors de fase d'1 bit. La part final de la tesis es centra en les toleràncies de fabricació i en els processo de microfabricació d'agrupacions d'antenes mil•limètriques. Les toleràncies de fabricació s'han estudiat en funció dels error d'amplitud i fase en cada element de l'agrupació, fixant-se en les pèrdues de guany, error d'apuntament, error en l'amplada de feix, errors en el nivell de lòbul secundari i en l'error en la relació axial. El procés de microfabricació de les diferents antenes dissenyades es presenta en detall. Els dissenys de l'antena CPW Patch reconfigurable en polarització i apuntament operant a les bandes Ka i V, s'han fabricat en la sala blanca del Cornell NanoScale Science & Technology Facility (CNF). Posteriorment, s'han caracteritzat l'aïllament i el temps de resposta dels interruptors RF-MEMS, i finalment, el coeficient de reflexió, el diagrama de radiació i la relació axial s'han mesurat a les bandes Ka i V per les antenes configurades en polarització lineal (LP) i circular (CP).Telecommunication services and radar systems are migrating to Millimeter-wave (MMW) frequencies, where wider bandwidths are available. Such migration requires the use of different technologies with the capability to operate at the MMW frequency band (30 to 300GHz), and more specifically at Ka- (26.5 to 40GHz), V- (50 to 75GHz) and W-band (75 to 110GHz). For many applications and more concretely those where the antenna is part of a mobile device, it is targeted the use of planar antennas for their low profile and low fabrication cost. A wide variety of requirements is translated into a reconfiguration capability and low losses within each application frequency bandwidth. To deal with the mentioned challenges, the MMW antenna dimensions, together with the materials, fabrication tolerances and reconfigurability capability lead to microfabrication processes. The aim of this thesis is the analysis of the mentioned concepts, materials, transmission lines geometries and switches in the MMW frequencies context and their final application in antenna designs compatible with microfabrication. Finally, specific designs are presented as a demonstration for three MMW applications: Satellite Communication Systems (SCS) at Ka-band, Wireless Personal Area Network (WPAN) at V-band and Automotive Radar at W-band. The first part of this thesis consist to analyze some MMW circuit technologies. The four most used materials at MMW frequencies (Polytetrafluoroethylene or Teflon (PTFE), Quartz, Benzocyclobuten polymer (BCB) and Low Temperature Co-fired Ceramic (LTCC)) have been presented and compared in terms of permittivity (εr) and loss tangent (tanδ). An study of the main transmission lines attenuation (microstrip, stripline and CPW) at high frequencies is included. Finally, an overview of the RF-MEMS switches is presented in comparison with PIN diodes and FETS switches. The second part presents different polarization and beam pointing reconfigurable array antennas. Two polarization-reconfigurable base-elements have been designed: CPW Patch antenna and 4-Qdime antenna. The first consists of a single reconfigurable element with integrated RF-MEMS switches, designed to operate at Ka- and V-band. The second antenna presented in this thesis has a composed architecture where the polarization reconfigurability is obtained by switching the phase feeding for each of the four linear polarized elements in the feed network with RF-MEMS switches. The 4-Qdime antenna has been designed to operate at V- and W-band. The two base-elements have been used to design two beam pointing reconfigurable antenna arrays. Using phased array techniques, beamsteering is computed and implemented with 1-bit discrete phase-shifter. The final part of the thesis is focused into the fabrication tolerances and microfabrication process of Millimeter-wave antenna arrays. The fabrication tolerances have been studied as a function of the amplitude and phase errors presented at each elements array, focusing on the gain loss, beam pointing error, Half-Power Beamwidth (HPBW) error, sidelobe level error and axial ratio error. The microfabrication process for the designed antennas is presented in detail. Polarization- and pointing- reconfigurable CPW Patch antenna operating at Ka- and V- band have been fabricated in a clean-room facility at Cornell NanoScale Science & Technology Facility (CNF). The RF-MEMS switches isolation and time response have been characterized. Finally, the reflection coefficient, radiation pattern and axial ratio have been measured at Ka- and V-band for the fabricated antennas configured in Linear Polarization (LP) and Circular Polarization (CP)

Performance enhancement of G-band micromachined printed antennas for MMIC integration

The objective of the work of this thesis is to design, fabricate, and characterise high performance micromachined antennas with fixed and reconfigurable bandwidth. The developed integrated antennas are suitable for MMICs integration at millimetre wave frequencies (G-band) on MMICs technology substrates (i.e GaAs, Si, InP). This work is done through a review of the scientific literature on the subject, and the design, simulation, fabrication and experimental verification, of various suitable designs of antenna. The novel design of the antennas in this work is based on elevated antenna structures in which the radiator is physically micromachined above the substrate. The antenna design schemes offer a suitable method to integrate an antenna with other MMICs. Further, this method eliminates undesired substrate effects, which degrades the antenna performance drastically. Also in this work we have for the first time realized different micromachined antenna topologies with different novel feeding mechanisms - offering more degrees of freedom for antenna design and enhancing the antenna performance. Experimental and simulation results are provided to demonstrate the effectiveness of the proposed antenna designs and topologies in this work. A new approach for fabricating printed antennas is introduced in this work to fulfil the fabrication process requirements. It provides a new method for the fabrication of 3-D multilevel structures with variable heights, without etching the substrate. Further, the height of the elevated structures can be specified in the process and can vary by several microns, regardless of the substrate used. This can be used to further enhance the bandwidth and gain of the antenna - avoiding substrate thinning and via holes, and increasing the fabrication yield. Thus, the elevated antenna can meet different application requirements and can be utilized as a substrate independent solution. In this work we have introduced the concept of reconfigurable antennas at millimetre wave band. Also, we have investigated various aspects associated with lowering the pull-down voltage and overcoming the stiction problem of MEMS switches required for the proposed reconfigurable antennas. This was achieved by developing MEMS technology which can be integrated with MMICs fabrication process. Two novel reconfigurable elevated patch antenna topologies were designed to demonstrate the developed technology and their performances were discussed. The result we obtained from this work demonstrates the feasibility of MEMS reconfigurable printed antennas at G-band frequencies. This will open a new field in MMICs technology and increasing system integration capabilities and functionality. The devolved technology in this thesis could be utilized in many unique applications including short range high data rate communication systems and high-resolution passive and active millimetre-wave imaging

RF-MEMS teknolojisi ile faz dizili anten yapımı

TÜBİTAK EEEAG Proje30.06.201

Tuneable RF MEMS components using SU-8

With the rapid progress in the wireless communication field, radio frequency microelectro- mechanical systems (RF MEMS) are seen as one of the promising technologies to replace the existing high power communication systems. MEMS based tuneable devices such as varactors and phase shifters offer many advantages over their conventional diode-based counterparts including low loss, low power consumption and high linearity. MEMS varactors in particular can be integrated into many reconfigurable modules such as switching and reconfigurable matching networks. Moreover, distributed MEMS transmission line (DMTL) phase shifters with their linear phase characteristic can be applied to wideband phased array antennas for microwave medical imaging which requires beam steering and high gain antenna systems. This thesis focuses on the design and development of two RF MEMS devices which are a high tuning ratio digital MEMS varactor and a low frequency DMTL phase shifter using SU-8 polymer. The design and simulation of a 4-bit and a 5-bit digital MEMS varactors have been carried out in the first phase of this study. One of the limitations of the digital MEMS varactors fabricated on silicon substrates is the high fringing field capacitance that reduces the overall capacitance ratios of the devices. To reduce the effect of the fringing fields, two methods have been proposed to elevate the varactors from the silicon substrate. In the first method, a 26.35 μm deep trench is etched in the silicon substrate under the 4-bit digital MEMS varactor which is able to achieve a high capacitance ratio of 35.7. In the 5-bit digital MEMS varactor design, SU-8 material is used to form a 20 μm thick separation layer between the varactor and the silicon substrate instead of the deep trench method applied in the 4-bit MEMS varactor. The simulated capacitance ratio of the 5-bit digital MEMS varactor is 34.8. Additionally, the SU-8 also serves as a sacrificial layer to release the MEMS bridges on the devices hence reducing the fabrication process compared to the conventional MEMS release process that uses oxide as the sacrificial material. To verify the performance of using the thick SU-8 dielectric layer in reducing the fringing field capacitance in the varactor design, single-bridge varactors with different lengths and widths have been fabricated and analysed. A novel truss bridge structure has been proposed in order to reduce the pull-in voltage of the varactors. It is found that by using the truss structure, the measured pull-in voltage of the bridge can be reduced by 12.5% compared to the conventional solid fixed-fixed bridge structure. However, due to the high residual stress from the fabrication process which causes the bridge to warp over its width, the achievable average down-state capacitance of the fabricated single-bridge varactor is limited to 211 fF compared to the simulated value of 1.28 pF. Nevertheless, the capacitance ratio of the device fabricated on the SU-8 layer increases by 56.75% over a similar device fabricated without the polymer which proves that the fringing field capacitance has been reduced. Furthermore, fabrication of the single-bridge MEMS varactors on low-resistivity silicon has been carried out with the use of SU-8 as the passivation layer without affecting the performances of the varactors. This finding can lead to the realisation of low-cost MEMS varactors in the future. The second part of this thesis investigates the development of distributed MEMS transmission line (DMTL) phase shifters for operation in the frequency range of 2 GHz to 4 GHz (S-band). The proposed phase shifters are a 2-bit and 3-bit digital DMTL phase shifters. One of the potential applications of the proposed phase shifters is for phased array antenna systems for microwave head imaging that requires wideband performance. The 2-bit and 3-bit DMTL phase shifters have been designed and simulated with 41 MEMS bridges and 105 MEMS bridges respectively. The simulated phase shifts of the 2-bit phase shifter design are 00, 900, 1800 and 2700 whereas for the 3-bit phase shifter, 8 phase shifts have been achieved namely 00, 450, 900, 1350, 1800, 2250, 2700 and 3150. To validate the performance of the proposed low frequency DMTL phase shifter, the 2-bit phase shifter design has been fabricated and analysed. The measured impedance matching of the phase shifter shows good performance with reflection coefficients of less than -10 dB across the operating frequency range for all the states of the phase shifter. The measured differential phase shifts of the device are 00, 17.890, 34.510 and 52.390. The lower measured differential phase shifts compared to the simulated values can be attributed to the warping of the bridges over their width which causes a formation of an air gap between the bridge and dielectric layer hence reducing the down-state capacitance of the varactors in the phase shifter. Nevertheless, this is the first DMTL phase shifter to achieve a maximum differential phase shift of 52.390 at 2.45 GHz. Based on the measured differential phase shifts, the phase shifter can provide a maximum steering angle of ±5.730 for a 4-element phased array antenna at 2.45 GHz. The maximum measured transmission loss of the phase shifter is -10.51 dB at 2.45 GHz. The high loss of the phase shifter is due to the skin depth effect since the co-planar waveguide (CPW) transmission line of the phase shifter is fabricated using 300 nm thick aluminium. Therefore, further investigation has been carried out to provide better estimation of the transmission loss of the phase shifter by fabricating a CPW transmission line with the same configuration to that of the transmission line in the fabricated phase shifter by using 2 μm thick aluminium. The measured loss of the transmission line is -2.39 dB which shows significant improvement over the loss obtained from the phase shifter. Moreover, several CPW transmission lines with different centre conductor’s widths have been fabricated and analysed to further reduce the losses of the transmission lines. An attenuation loss of only 0.122 dB/cm has been achieved using a 500 μm-width centre conductor in the fabricated CPW transmission line which can lead to the realisation of a low-loss DMTL phase shifter for low microwave frequency range. The characterisation and optimisation of the varactors and phase shifters using SU-8 provide the initial step towards the development of tuneable RF MEMS devices for wide range of applications including wireless communications and radar systems. Moreover, the proposed DMTL phase shifters for operation at the lower end of microwave spectrum particularly in the frequency range of 2 GHz to 4 GHz are vital for the realisation of wideband phased array antennas for microwave medical imaging applications

Performance enhancement of G-band micromachined printed antennas for MMIC integration

The objective of the work of this thesis is to design, fabricate, and characterise high performance micromachined antennas with fixed and reconfigurable bandwidth. The developed integrated antennas are suitable for MMICs integration at millimetre wave frequencies (G-band) on MMICs technology substrates (i.e GaAs, Si, InP). This work is done through a review of the scientific literature on the subject, and the design, simulation, fabrication and experimental verification, of various suitable designs of antenna. The novel design of the antennas in this work is based on elevated antenna structures in which the radiator is physically micromachined above the substrate. The antenna design schemes offer a suitable method to integrate an antenna with other MMICs. Further, this method eliminates undesired substrate effects, which degrades the antenna performance drastically. Also in this work we have for the first time realized different micromachined antenna topologies with different novel feeding mechanisms - offering more degrees of freedom for antenna design and enhancing the antenna performance. Experimental and simulation results are provided to demonstrate the effectiveness of the proposed antenna designs and topologies in this work. A new approach for fabricating printed antennas is introduced in this work to fulfil the fabrication process requirements. It provides a new method for the fabrication of 3-D multilevel structures with variable heights, without etching the substrate. Further, the height of the elevated structures can be specified in the process and can vary by several microns, regardless of the substrate used. This can be used to further enhance the bandwidth and gain of the antenna - avoiding substrate thinning and via holes, and increasing the fabrication yield. Thus, the elevated antenna can meet different application requirements and can be utilized as a substrate independent solution. In this work we have introduced the concept of reconfigurable antennas at millimetre wave band. Also, we have investigated various aspects associated with lowering the pull-down voltage and overcoming the stiction problem of MEMS switches required for the proposed reconfigurable antennas. This was achieved by developing MEMS technology which can be integrated with MMICs fabrication process. Two novel reconfigurable elevated patch antenna topologies were designed to demonstrate the developed technology and their performances were discussed. The result we obtained from this work demonstrates the feasibility of MEMS reconfigurable printed antennas at G-band frequencies. This will open a new field in MMICs technology and increasing system integration capabilities and functionality. The devolved technology in this thesis could be utilized in many unique applications including short range high data rate communication systems and high-resolution passive and active millimetre-wave imaging.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Antenna integration for wireless and sensing applications

As integrated circuits become smaller in size, antenna design has become the size limiting factor for RF front ends. The size reduction of an antenna is limited due to tradeoffs between its size and its performance. Thus, combining antenna designs with other system components can reutilize parts of the system and significantly reduce its overall size. The biggest challenge is in minimizing the interference between the antenna and other components so that the radiation performance is not compromised. This is especially true for antenna arrays where the radiation pattern is important. Antenna size reduction is also desired for wireless sensors where the devices need to be unnoticeable to the subjects being monitored. In addition to reducing the interference between components, the environmental effect on the antenna needs to be considered based on sensors' deployment. This dissertation focuses on solving the two challenges: 1) designing compact multi-frequency arrays that maintain directive radiation across their operating bands and 2) developing integrated antennas for sensors that are protected against hazardous environmental conditions. The first part of the dissertation addresses various multi-frequency directive antennas arrays that can be used for base stations, aerospace/satellite applications. A cognitive radio base station antenna that maintains a consistent radiation pattern across the operating frequencies is introduced. This is followed by multi-frequency phased array designs that emphasize light-weight and compactness for aerospace applications. The size and weight of the antenna element is reduced by using paper-based electronics and internal cavity structures. The second part of the dissertation addresses antenna designs for sensor systems such as wireless sensor networks and RFID-based sensors. Solar cell integrated antennas for wireless sensor nodes are introduced to overcome the mechanical weakness posed by conventional monopole designs. This can significantly improve the sturdiness of the sensor from environmental hazards. The dissertation also introduces RFID-based strain sensors as a low-cost solution to massive sensor deployments. With an antenna acting as both the sensing device as well as the communication medium, the cost of an RFID sensor is dramatically reduced. Sensors' strain sensitivities are measured and theoretically derived. Their environmental sensitivities are also investigated to calibrate them for real world applications.Ph.D.Committee Chair: Tentzeris, Emmanouil; Committee Member: Akyildiz, Ian; Committee Member: Allen, Mark; Committee Member: Naishadham, Krishna; Committee Member: Peterson, Andrew; Committee Member: Wang, Yan

Autonomous smart antenna systems for future mobile devices

Along with the current trend of wireless technology innovation, wideband, compact size, low-profile, lightweight and multiple functional antenna and array designs are becoming more attractive in many applications. Conventional wireless systems utilise omni-directional or sectored antenna systems. The disadvantage of such antenna systems is that the electromagnetic energy, required by a particular user located in a certain direction, is radiated unnecessarily in every direction within the entire cell, hence causing interference to other users in the system. In order to limit this source of interference and direct the energy to the desired user, smart antenna systems have been investigated and developed. This thesis presents the design, simulation, fabrication and full implementation of a novel smart antenna system for future mobile applications. The design and characterisation of a novel antenna structure and four-element liner array geometry for smart antenna systems are proposed in the first stage of this study. Firstly, a miniaturised microstrip-fed planar monopole antenna with Archimedean spiral slots to cover WiFi/Bluetooth and LTE mobile applications has been demonstrated. The fundamental structure of the proposed antenna element is a circular patch, which operates in high frequency range, for the purpose of miniaturising the circuit dimension. In order to achieve a multi-band performance, Archimedean spiral slots, acting as resonance paths, have been etched on the circular patch antenna. Different shapes of Archimedean spiral slots have been investigated and compared. The miniaturised and optimised antenna achieves a bandwidth of 2.2GHz to 2.9GHz covering WiFi/Bluetooth (2.45GHz) and LTE (2.6GHz) mobile standards. Then a four-element linear antenna array geometry utilising the planar monopole elements with Archimedean spiral slots has been described. All the relevant parameters have been studied and evaluated. Different phase shifts are excited for the array elements, and the main beam scanning range has been simulated and analysed. The second stage of the study presents several feeding network structures, which control the amplitude and phase excitations of the smart antenna elements. Research begins with the basic Wilkinson power divider configuration. Then this thesis presents a compact feeding network for circular antenna array, reconfigurable feeding networks for tuning the operating frequency and polarisations, a feeding network on high resistivity silicon (HRS), and an ultrawide-band (UWB) feeding network covering from 0.5GHz to 10GHz. The UWB feeding network is used to establish the smart antenna array system. Different topologies of phase shifters are discussed in the third stage, including ferrite phase shifters and planar phase shifters using switched delay line and loaded transmission line technologies. Diodes, FETs, MMIC and MEMS are integrated into different configurations. Based on the comparison, a low loss and high accurate Hittite MMIC analogue phase shifter has been selected and fully evaluated for this implementation. For the purpose of impedance matching and field matching, compact and ultra wideband CPW-to-Microstrip transitions are utilised between the phase shifters, feeding network and antenna elements. Finally, the fully integrated smart antenna array achieves a 10dB reflection coefficient from 2.25GHz to 2.8GHz, which covers WiFi/Bluetooth (2.45GHz) and LTE (2.6GHz) mobile applications. By appropriately controlling the voltage on the phase shifters, the main beam of the antenna array is steered ±50° and ±52°, for 2.45GHz and 2.6GHz, respectively. Furthermore, the smart antenna array demonstrates a gain of 8.5dBi with 40° 3dB bandwidth in broadside direction, and has more than 10dB side lobe level suppression across the scan. The final stage of the study investigates hardware and software automatic control systems for the smart antenna array. Two microcontrollers PIC18F4550 and LPC1768 are utilised to build the control PCBs. Using the graphical user interfaces provided in this thesis, it is able to configure the beam steering of the smart antenna array, which allows the user to analyse and optimise the signal strength of the received WiFi signals around the mobile device. The design strategies proposed in this thesis contribute to the realisation of adaptable and autonomous smart phone systems

Millimeter-Wave Substrate Integrated Waveguide Antenna and Front-End Techniques for Gigabyte Point-to-Point Wireless Services

RÉSUMÉ La relativement faible absorption atmosphérique dans les bandes de fréquences E et W a permis le développement de nombreuses applications sans-fil. Les bandes de fréquences de 71-76 GHz, 81-86 GHz et 94.1-97 GHz sont toutes assignées au spectre de communication sans-fil gigabyte par la Federal Communication Commission (FCC) des États-Unis. Lorsque la fréquence augmente vers la région des ondes millimétriques, l’efficacité et la qualité des lignes micro-ruban sont affectées par de sérieuses pertes de transmission et par l’interférence inter-signaux. D’un autre côté, la technologie des guides d’ondes classique est demeurée populaire pour la conception de systèmes haute perfomance dans la bande E/W. Cependant, cette technologie n’est pas appropriée pour une production à grande échelle et à faible coût à cause de sa structure encombrante et coûteuse. De plus, la structure non-planaire des guide d’ondes rend difficile la connection à des composantes planaires actives ainsi qu’à d’autres lignes planaires telles que les lignes micro-ruban et les guides d’ondes coplanaires (CPW). Afin de remédier à ce problème, les circuits intégrés aux substrats (SIC) ont été proposés comme une solution à faible coût, à efficacité élevée, planaire et intégrée au substrat pour des applications à hautes-fréquences. Les guides d’ondes intégrés aux substrats (SIW), faisant partie de la famille des SIC, possède non seulement les avantages des guides d’ondes rectangulaires mais aussi d’autres bénéfices comme un faible coût, une petite taille, un poids léger et la facilité de fabrication par les techniques de fabrication des PCB ou d’autres techniques. Dans cette thèse, nous élargissons la recherche sur les SIW en proposant et développant une variété d’antennes innovatrices, de réseaux d’antennes et de composantes passives millimétriques qui sont appliqués à la conception et à la démonstration de réseaux d’antennes intégrés et d’étages d’entrée de systèmes de communication en bande E/W. Les contributions scientifiques principales du présent travail peuvent être résumées comme suit: Un réseau d’antenne 4x4 utilisant la technologie des guides d’ondes intégrés au substrat (SIW) pour la conception de son réseau d’alimentation est proposé et démontré. Des fentes longitudinales gravées sur la surface métallique du dessus du SIW sont utilisées pour alimenter les éléments du réseau d’antennes. Des cubes composés d’un matériau diélectrique à faible permittivité sont placés au-dessus de chaque réseau d’antenne 1x4 afin d’augmenter le gain des antennes patch. La largeur de bande de deux réseaux d’antennes 4x4 est d’environ 7.5 GHz (94.2-101.8 GHz) avec un gain de 19 dBi.----------ABSTRACT The relatively low atmospheric absorption over E-band and W-band (frequency window) has been spurred many wireless applications. Frequency bands of 71-76 GHz, 81-86 GHz, and 94.1-97 GHz are all allocated by the US Federal Communication Commission (FCC) as parts of gigabyte wireless spectrum. As frequency increases to millimeter wave region, the efficiency and quality of microstrip lines suffer from serious transmission losses and signal interferences. On the other hand, classical waveguide technology has been popular in the design of high-performance millimeter-wave systems at E/W-band. However, this technology is not suitable for low-cost and mass production because of its expensive and bulky structure. In addition, the non-planar structure of waveguide makes it difficult to get connected to planar active components and other planar lines such as microstrip line and coplanar waveguide (CPW). To overcome this bottleneck problem, substrate integrated circuits (SICs) have been proposed as low-cost and high-efficient integrated planar structures for high-frequency applications. Substrate integrated waveguide (SIW), which is part of the SICs family, has manifested not only the advantages of rectangular waveguide but also other benefits such as low cost, compact size, light weight, and easy fabrication using PCB or other processing techniques. In this Ph.D. thesis, we extend the research of SIW to the proposal and development of various innovative antennas, antenna arrays and millimetre-wave passive components, which are applied to the design and demonstration of integrated antenna arrays and E/W-band front-end sub-systems. The principal scientific contributions of this thesis work can be summarized in the following: A 4×4 antenna array is proposed and demonstrated using substrate-integrated waveguide (SIW) technology for the design of its feed network. Longitudinal slots etched on the SIW top metallic surface are used to drive the array antenna elements. Dielectric cubes made of low-permittivity material are placed on top of each 1×4 antenna array to increase the gain of circular patch antenna elements. Measured impedance bandwidths of two 4×4 antenna arrays are about 7.5 GHz (94.2–101.8 GHz) with 19 dBi gain. Design of planar dielectric rod antenna is proposed and studied, which is fed by Substrate Integrated Non-Radiative Dielectric (SINRD) waveguide. This antenna presents numerous interesting features such as broad bandwidth (94-104 GHz), relatively high and stable gain, use of high dielectric constant substrate, and substrate-oriented end-fire radiation

Structure and Optimisation of Liquid Crystal based Phase Shifter for Millimetre-wave Applications

The delivery of tunable millimetre-wave components at 60GHz is of research and development interests with the advent of 5G era. Among applications such as high-data-rate wireless communications, high-precision automotive radars and hand-gesture sensing, variable phase shifters are vital components for antenna arrays to steer an electromagnetic beam without mechanical movement. However, present microwave technology has limited scope in meeting more and more stringent requirements in wavefront phase control and device performance for those cutting-edge applications in the millimetre-wavelength range. Although some existing microwave switchable techniques (such as RF MEMS and solid-state p-i-n diodes) can offer ultra-fast speed for phase modulation, their binary beam-steering nature is resolution-limited and thereby degrades the beam-scanning performance. In response to this, continuously-tunable phase shifting can be realised by using tunable dielectric materials such as ferroelectric BST and liquid crystals (LCs). BST thin films can offer relatively fast switching and modest tunability. However, the increased dielectric loss beyond 10GHz impedes their implementation for higher frequency applications. By comparison, liquid crystals (LCs) have drawn attention in recent years because of their continuous tunability as well as low losses especially at millimetre-wavebands. The principle of shifting the phase continuously is based on the shape anisotropy of LC molecules for variable polarizabilities and hence tunable dielectric constants, which allows wave speed to be controlled with ease by a low-frequency field of only up to 10V. However, LC-based tunable delay lines are not well established in the frequency regime of 60GHz-90GHz because of the limited status of LC microwave technology in which most of the LC based devices have been designed for below 40GHz. It is the aim of this PhD research to bridge the gap and address future societal needs based on our group’s focus and experience in developing cutting-edge LC-based agile microwave components. In this work, a liquid crystal (LC) based 0-180˚continuously-variable phase shifter is developed with insertion loss less than -4.4dB and return loss below -15dB across a wide spectrum from 54GHz to 67GHz. The device is driven by a 0-10V AC bias and structured in a novel enclosed coplanar waveguide (ECPW) including an enclosed ground plate in the design, which significantly reduces the instability due to floating effects of the transmission line. This structure screens out interference and stray modes, allowing resonance-free quasi-TEM wave propagation up to 90GHz. The tunable ECPW is optimised by competing spatial volume distribution of the millimetre-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics and minimising the total of dielectric volumetric loss and metal surface loss for a fixed phase-tuning range. A variety of influences affecting the actual device performance are studied, experimented and optimised. Fabricated prototypes exhibit wideband low-loss performance and 0-π continuous tuning with low power consumptions and high linearity compared with the state-of-the-arts. Potentially, the ECPW-fed phased antenna array will be incorporated with advanced beam-forming algorithms to develop compact beam-steering systems of improved performances and targeted for ultra-high-data-rate wireless communications, inter-satellite communications, current road safety improvement, futuristic autonomous driving, and other smart devices such as the hand-gesture recognition

Substrate Integrated Waveguide Antenna Applications

The research objective of this thesis is to provide a better solution for signal interference and reduce the size of waveguide antenna. The background investigations of different waveguide fabrication technologies and switch control methods are detailed in the introductory part of this thesis. Several novel substrate integrated waveguide (SIW) antennas for different purpose are demonstrated in the body of the thesis. The designs are mainly divided into two kinds. The first focuses on the switch beam SIW antennas working at 2.4 GHz frequency band. Compared to the corresponding waveguide antennas of multiple-input and multiple-output (MIMO), phased array and switch beam, the proposed SIW antennas have advantages in compact size, easy fabrication and high gain. By DC biasing the surface mounted PIN diodes, the waveguide slots radiate at diode-off state of reverse bias, and are shielded at diode-on state of forward bias. Based on different requirement, the SIW antennas can achieve two-direction, four-direction and six-direction transmission. The gain can be easily changed by extending the size of reflector walls. The second focuses on reducing the volume of SIW antennas, working at 5 GHz frequency band. A new folded SIW antenna is introduced. By folded the antenna front end part to second layer, the SIW antenna reduces the total length by the size of one-quarter guided wavelength. This folded antenna can radiate either monopole mode or dipole mode, based on the metal surface area. Another two new SIW antennas reduce the total length by directly cutting the front-end part at the slot center. By utilized the intrinsic coupling radiation, the SIW antennas use two half-length slots at different broad-wall plane to achieve 360 degree propagation and wide-band end-fire radiation