Planar beam-forming antenna array for 60-GHz broadband communication

The 60-GHz frequency band can be employed to realise the next-generation wireless high-speed communication that is capable of handling data rates of multiple gigabits per second. Advances in silicon technology allow the realisation of low-cost radio frequency (RF) front-end solutions. Still, to obtain the link-budget that is required for wireless gigabit-per-second communication, antenna arrays are needed that have sufficient gain and that support beam-forming. This requires the realisation of antenna arrays that maintain a high radiation efficiency while operating at millimeter-wave frequencies. Moreover, the antenna array and the RF front-end should be integrated into a single low-cost package that can be realised in a standard production process. In this thesis, antenna solutions have been presented that meet these requirements. This work covers the complete development cycle, viz modelling, design, optimisation, manufacturing, measurement and verification for three antenna prototype generations. An in-depth view of each development step is provided, while the combined work provides an overview of millimeter-wave antenna development. Modelling is a crucial step in the development cycle and has been discussed in Chapter 2. The production processes that are used for antenna design and packaging realise planar multi-layered structures. Therefore, the modelling of electromagnetic (EM) structures in stratified media has been considered. First, the Green’s function for stratified media has been derived. Second, a MoM-based approach has been proposed that provides an accurate analysis of the physical behaviour of these structures. Special attention has been given to the analysis of surface waves that propagate in the planar geometry, because they can significantly affect the radiation efficiency of planar antennas. The resulting model provides a computationally efficient tool (Spark) for the analysis and design of a wide range of planar antenna topologies. The first prototype is the balanced-fed aperture-coupled patch (BFACP) antenna element, that employs a unique topology and therefore exhibits excellent performance regarding bandwidth and radiation efficiency. The modelling and design of this antenna has been discussed in Chapter 3. It has been shown that the use of two coupling slots improves the bandwidth of the antenna as well as the radiation efficiency. Simultaneously, the back radiation is significantly reduced by employing a reflector element. The resulting antenna design has a measured bandwidth of 15% in combination with a radiation efficiency that is larger than 80% and an accompanying measured gain of 5.6 dBi. In Chapter 3, an extension of the BFACP antenna element has been presented that supports dual polarisation and/or circular polarisation as well. The proposed BFACP antenna designs can be employed both as single-element antenna and as a building block for antenna arrays. Obviously, the accurate measurement of the manufactured antenna prototypes is of importance for verification of both the modelling methods and the antenna designs. For this purpose, specific measurement setups have been designed. In Chapter 4 these setups have been introduced, motivated and explained. To obtain a reliable interconnection between the measurement equipment and the antenna under test, RF probes have been employed. Additional transitions (coplanar waveguide to microstrip transition, balun) have been designed to convert the single-ended signal of the measurement equipment to the balanced signal that is required by the antenna under test. Moreover, a far-field radiation pattern measurement setup has been developed from scratch which is completely tailored for the measurement of millimeter-wave antennas and beam-forming antenna arrays. It has been shown that these setups provide reliable measurement data that is in good agreement with the results obtained from the derived models. To maximise the performance of the antenna, an optimisation algorithm has been presented in Chapter 5 that gives the designer the flexibility to obtain the best antenna design for the considered application. This algorithm extends the derived EM model of the BFACP antenna (Chapter 3) to include sensitivity information about design parameters. The sensitivity has been employed to jointly optimise the bandwidth and the radiation efficiency of the antenna element. In Chapter 6, the optimised antenna element is used in the design of antenna arrays. Here, the modelling of beam-forming antenna arrays is discussed and the performance of several array configurations is compared. It has been concluded that a 6-element circular array shows best performance in terms of gain and radiation efficiency. Moreover, the mutual coupling between the elements of this array is low such that the active reflection coefficient remains well below -10 dB throughout the entire scan range. A second prototype has been designed that demonstrates beam-forming. For this prototype, 6-element circular arrays have been designed in combination with fixed feed networks that provide each antenna element with an RF signal that has the appropriate phase for beam-forming to a specific angle. The performance of these antenna arrays has been investigated in terms of radiation efficiency, bandwidth and gain. The prototype has a maximum measured gain of 11.8 dBi for broadside scan and it has been shown that these antenna arrays can be readily employed for the realisation of adaptive beam-forming at millimeter-wave frequencies. Chapter 7 discusses the packaging of the transceiver. First, the package requirements are listed and several package topologies are discussed. For example, the performance of superstrate topologies is analysed. Additionally, a package is proposed that embeds the BFACP antenna. This package combines ceramic-based layers and teflon-based layers. The ceramic-based layers provide the package with stiffness and are used to realise the RF feed network, whereas the teflon-based layers are employed to allow an antenna design that has a high radiation efficiency. For a high-performance package design, it is important that the electrical properties of the materials used is welldefined. Therefore, special efforts have been undertaken to characterise the electrical material properties of the materials used at millimeter-wave frequencies. For this purpose, ring resonators have been designed. Measurement results indicate that the electrical properties at higher frequencies can differ significantly from the values that are specified by the manufacturer for an operating frequency of 10 GHz. To demonstrate the performance of the BFACP antenna in a package configuration, a third prototype has been developed, in which the BFACP antenna is packaged in combination with active electronics. This prototype demonstrates that the antenna can be embedded in a package that contains not only the antenna, but also the RF electronics, RF feed network and control circuitry. In the prototype, the BFACP antenna has been connected to a power amplifier that has been realised in CMOS technology. The PA has been connected to the RF feed through a flip-chip interconnection process. It has been demonstrated that the proposed packaging topology results in an efficient transmitter. In conclusion, three antenna prototype generations have been presented and it is demonstrated that the presented concepts can be readily used for the design of a transceiver package that embeds a beam-forming antenna array and that supports gigabit-per-second communication

Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications

Metal surface tolerant conformal low-profile plastic embedded antennas for automotive applications

Mit der rasanten Zunahme drahtloser Dienste und dem Einsatz von Antennendiversitätstechniken zur Erzielung höherer Datenraten oder Dienstzuverlässigkeit ist die Zahl der in Pkw zu installierenden Antennen nicht mehr unbedeutend und nimmt weiter zu. Gleichzeitig wird es immer schwieriger, geeignete Montageplätze für diese Antennen zu finden, da die Zahl der Montageplätze im Auto nicht parallel zur Zahl der zu installierenden Antennen gewachsen ist; Autos sind nach wie vor meist Metallkästen, mit einigen wenigen Kunststoffteilen und Glasscheiben die die Integration von Antennen ermöglichen. Die meisten dieser Teile wurden bereits zu diesem Zweck verwendet, die B-Säulen-Kunststoffabdeckungen wurden jedoch bisher nicht für die Antennenintegration berücksichtigt. In dieser Arbeit werden nicht nur die Vorteile der B-Säulen-Kunststoffabdeckungen als Antenneneinbauort gegenüber anderen Orten hervorgehoben, sondern auch die damit verbundenen Herausforderungen untersucht, insbesondere der begrenzte Platz für die Antennenintegration und die unmittelbare Nähe der eingebauten Antenne zum Metallchassis des Fahrzeugs. Letzteres führt zu einer starken elektromagnetischen Kopplung zwischen der Antenne und der Fahrzeugkarosserie, was sich auf die Antenneneigenschaften wie Impedanzanpassung und realisierten Gewinn auswirkt. In den folgenden Kapiteln werden die zugrundeliegenden Entwurfsprinzipien, die Theorie und die Messungen neuartiger, flacher, konformer und metalloberflächentoleranter Mobilfunkantennen vorgestellt, nämlich die Einzelband-Di-Patch-Antenne und eine koplanar gestapelte, mit Mikrostreifenleitungen gekoppelte Multibandantenne, die die oben genannten Herausforderungen adressieren und überwinden. Zusätzlich wird in der zweiten Hälfte dieser Arbeit eine high impedance surface basierte Dipolantennenlösung vorgestellt. Die Simulations- und Messergebnisse der nicht integrierten und der integrierten Versionen der vorgestellten Antennen, einschließlich der LTE-MIMO-Datenratenmessungen, die im vorletzten Kapitel vorgestellt werden, sprechen nicht nur für die Eignung dieser Antennen für flache, metallnahe Oberflächenanwendungen im Allgemeinen, sondern zeigen auch, dass die B-Säulen- Kunststoffabdeckungen einen sehr geeigneten neuen Antennenintegrationsort für mobile Kommunikationsanwendungen im Automobil darstellen.With a rapid increase in the number of wireless services, and the utilization of antenna diversity techniques to achieve enhanced data rates or service reliability, the number of antennas that need to be installed in passenger cars is not insignificant any more, and only sees a rising trend. At the same time, finding suitable mounting locations for these antennas has become ever more challenging, because the number of such locations on a car has not grown parallelly to the number of antennas that need to be installed; cars are still mostly metal boxes, with a few plastic parts and the glass windows that allow for antenna integration. While most of these parts have already been utilized for embedding antennas, the plastic parts that were overlooked till now were the B-column plastic covers. In addition to highlighting the advantages of using the B-column plastic covers as an antenna embedding location over other locations, this work takes a comprehensive look into the challenges associated with the same, specifically the limited space for antenna integration and the close proximity of the embedded antenna to the car metal chassis. The latter introduces a strong electro- magnetic coupling between the antenna and the car body, consequently impacting antenna properties like impedance matching and realized gain. The upcoming chapters present the underlying design principles, theory, and measurements of novel, low-profile, conformal and metal surface tolerant mobile communications antennas, namely, the single band di-patch antenna and a co-planar stacked microstrip line coupled multi-band antenna, that suitably address and overcome the aforementioned challenges. Additionally, a high impedance surface based dipole antenna solution is also presented in the later half of this thesis. The simulation and measurement results of the bare and the integrated versions of the presented antennas, including LTE-MIMO data rate measurements presented in the penultimate chapter, not only speak for the suitability of these antennas for low-profile, close-to-metal surface applications in general, but also show that the B-column plastic covers present a highly suitable new antenna integration location for automotive mobile communications applications

Development and Validation of a Method of Moments approach for modeling planar antenna structures

In this dissertation, a Method of Moments (MoM) Volume Integral Equation (VIE)-based modeling approach suitable for a patch or slot antenna on a thin finite dielectric substrate is developed and validated. Two new key features of this method are the use of proper dielectric basis functions and proper VIE conditioning, close to the metal surface, where the surface boundary condition of the zero tangential-component must be extended into adjacent tetrahedra. The extended boundary condition is the exact result for the piecewise-constant dielectric basis functions. The latter operation allows one to achieve a good accuracy with one layer of tetrahedra for a thin dielectric substrate and thereby greatly reduces computational cost. The use of low-order basis functions also implies the use of low-order integration schemes and faster filling of the impedance matrix. For some common patch/slot antennas, the VIE-based modeling approach is found to give an error of about 1% or less in the resonant frequency for one-layer tetrahedral meshes with a relatively small number of unknowns. This error is obtained by comparison with fine finite- element method (FEM) simulations, or with measurements, or with the analytical mode matching approach. Hence it is competitive with both the method of moments surface integral equation approach and with the FEM approach for the printed antennas on thin dielectric substrates. Along with the MoM development, the dissertation also presents the models and design procedures for a number of practical antenna configurations. They in particular include: i. a compact linearly polarized broadband planar inverted-F antenna (PIFA); ii. a circularly polarized turnstile bowtie antenna. Both the antennas are designed to operate in the low UHF band and used for indoor positioning/indoor geolocation

Analysis and Design of Footwear Antennas

Wearable technologies are found in an increasing number of applications including sport and medical monitoring, gaming and consumer electronics. Sensors are used to monitor vital signs and are located on various parts of the body. Footwear sensors permit the collection of data relating to gait, running style, physiotherapy and research. The data is sent from sensors to on-body hubs, often using wired technology, which can impact gait characteristics. This thesis describes the design of footwear antennas for wireless sensor telemetry. The work addresses the challenges of placing antennas close to the foot as well as the proximity to the ground. Guidelines for polarization are presented. The channel link between footwear and wrist is investigated for both narrowband and wideband channels across different frequencies. The effects of the body proximity and movement were gauged for walking subjects and are described in terms of the Rician Distribution K-factor. Different antenna solutions are presented including UWB antennas on various footwear locations as well as 433 MHz integrated antennas in the insole. Both directional and omnidirectional antennas were considered for UWB and the evaluation was for both time-domain and frequencydomain. The research established new ideas that challenge the old paradigm of the waist as the best hub position, demonstrating that a hub on the footwear using directional antennas outperforms a hub on the waist using an omnidirectional antenna. The cumulative distribution functions of measured path gains are evaluated and the results are described in terms of the achievable minimum data rate considering the Body Area Network standard

Small Electrical, Mechanical, and Biomechanical Systems of Electromagnetic Radiation

This thesis presents novel solutions to certain emerging problems related to electrically small radiating systems and antennas for effectively increasing the radiation efficiency and/or bandwidth of physically small antennas radiating at low frequencies. The thesis introduces the concept of fragmented antennas for the first time. It also provides a completely novel solution for implementation of mechanical antennas with frequency multiplication and phase modulation capabilities for the first time. These concepts are borrowed to develop mechano-electromagnetic radio concept for biological cells to explain how communication can occur in community of cells. The proposed mechanical antenna provides unique capabilities for communication at very-low frequency band (3-30 kHz) and lowers. In mechanical antennas, the radiation is mainly induced through accelerating (rotating) electric charges or permanent magnets by means of fast electric motors. This work presents a novel phase modulation and frequency multiplication scheme for radiation at frequencies up to seven time rotation frequency of their mechanical motor and at the same time provides phase modulation capability. This is done by incorporating two pairs of orthogonal bow-tie shape high-μ magnetic material plates through which super magnetic bar is rotated by a fast electric motor. By moving the angular position of the magnetic plates, it is shown that the phase and amplitude of the EM signal can be modulated. This thesis also reports on the feasibility of formation of an electrically large antenna at low frequencies using a number of miniaturized antennas through electromagnetic coupling for achieving high bandwidth. The proposed fragmented antenna system is intended for a linear flight formation of small UAVs carrying individual antennas. Inductively end-loaded folded dipole antennas are used as the individual antenna that can provide radiation at the desired frequency over a narrow bandwidth. The overall dimensions and the total mass of the individual elements are 12×10×10cm (0.096λ_0× 0.08λ_0× 0.08λ_0 at 240MHz) and 18g, respectively. Each miniaturized antenna can only provide 2.4 MHz (~1%) bandwidth and 25 Ω input impedance. It is shown that a cluster of three of such elements operating in the vicinity of each other, the center element can provide 18.4 MHz bandwidth (an improvement of 770%) through inductive coupling while the other two elements are loaded with optimal reactive elements. The fundamentals of operation of embedded radios within cellular structures and biofilms is based on mechanical antennas. Certain bacterial cells within their biofilms are equipped with elastic helical fibers called amyloid fibrils which pose permanent electric dipole. We propose that the cells transmit electromagnetic (EM) signal to their surrounding environment through mechanical vibration of these fibrils. Different vibrational modes associated with fibrils including cantilever beam mode, longitudinal spring vibrational mode, and transverse spring modes are investigated indicating potential EM signaling within kHz-MHz, GHz, and sub-THz ranges, respectively. A novel and theoretical Multiphysics model based on coupled system of electrical and mechanical structures is also proposed to study the impact of this signaling on crowd of fibrils in a biofilm sample. Next, to demonstrate the advantage of EM-based communication, using communication channel theory, we have compared performance of EM signaling with its biochemical counterpart (quorum sensing) and shown that EM signaling provides much higher data rate, 5 to 7 orders of magnitude, and over much longer ranges. Thus, it could be potentially more efficient and a preferred method for communication among cells.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/168002/1/nbarani_1.pd

Application of High Impedance Surfaces to Improve Radiofrequency Coil Performance for 7-Tesla Magnetic Resonance Imaging

In modern medicine Magnetic Resonance Imaging (MRI) has been widely used for the detection of diseases, like brain tumor, breast cancer or heart disease, to name a few. In order to improve the image quality, the concept of high-field and ultra-high-field imaging has been intensively investigated over the last three decades. However, associated with the increased magnetic field strength various problems and challenges occur. The inhomogeneous B1-field distribution and decreased penetration depth into the subject to be imaged are two critical issues. The concept of High Impedance Surface (HIS) has been successfully applied in a number of antenna applications. The most relevant achievements are an improved radiation efficiency especially for low profile antennas and a decreased mutual coupling between adjacent antennas or antenna ports. In this thesis, an approach to improve the B1 distribution of radiofrequency (RF) coils in terms of homogeneity and penetration depth by utilizing a HIS shield is presented. First, fundamental investigations are carried out to verify the concept of using a shield with large surface impedance, which is modeled here by a Surface Impedance Boundary Condition (SIBC), to enhance the B1 distribution of RF coils. Different SIBCs are considered and their effects on the electromagnetic (EM) field of RF coils are studied. Next, the shield with a large surface impedance is realized by a periodic HIS structure, where two approaches (multi-layer uni-planar and mushroom-like topologies) are introduced in the lattice design of the HIS structure. The proposed HIS structures are evaluated via their reflection phase and dispersion diagram, which are based on unit cell simulation; as well as the bandgap property based on transmission line (TL) models. Then, the realized HIS shield based on the uni-planar topology is applied to the RF coils, and the concept of using HIS shield to improve the B1 distribution is confirmed through full-wave simulations and experimental results. Additionally, we consider another important parameter for a multi-channel dipole coil array consisting of several array elements—the coupling characteristic of the coil array, especially between the neighboring elements (the worst case scenario). The last chapter provides a brief summary and discussion, as well as an outlook of the future work

Analysis and design of the twisted loop antenna topology for mobile communications

The handset product has been styled in successive years to reach more compact sizes and there has as a result been a reduction in volume available to house antennas; therefore size/performance trade-offs have had to become accommodated. Some of the issues antenna engineers are currently confronted with include; frequency shifting due to the antenna not being isolated from the handset, far field pattern deformation due to close proximity effects from the energy absorbing human tissues, distortion caused by noise from electronic components that share the handheld platform. What is required is antenna technology, which maintains a high enough performance despite the escalating restrictions imposed by the demands of the market. Research is performed on a twisted loop antenna topology that possesses an integral balun as part of its structure. Two rudimentary designs are utilised in the research, a simple bifilar structure that can be adapted for GSM, peN, Bluetooth and W-LAN applications, and a quadrifilar helix structure for use in GPS. Both structures are based on existing industrial dielectricloaded antenna structures but are modelled as novel air-loaded structures using a commercially available Method of Moments (MoM) electromagnetic simulator. In this fashion, the antennas could be generated quickly with low computational requirements. A parametric study is performed on the bifilar antenna structure to gain an enhanced understanding of the twisted loop topology. Once this understanding is achieved proposed modifications to the structure are implemented to improve the performance of the antenna. The main subject of improvement is the broadening of bandwidth as normally dielectric-loaded antennas have inherent narrow bandwidth. Any improvements made on the air-loaded structures could be tested on dielectric structures in future research. The most successful novel approach attempted to increase the bandwidth in the twisted loop structure was the insertion of parasitic helices to create a coupled multi-pole filter response. In conjunction with the work performed on the bifilar, an air-loaded GPS quadrifilar helix antenna was also modelled. A method for inducing circular polarisation is proposed and then by the insertion of parasitics into the quadrifilar helix design a novel dual-band dual-polarised antenna is presented. Finally measurements are made to demonstrate the advantageous properties the dielectric-loaded GPS antenna has over conventional GPS antennas.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Real-time and portable microwave imaging system

Microwave and millimeter wave imaging has shown tremendous utility in a wide variety of applications. These techniques are primarily based on measuring coherent electric field distribution on the target being imaged. Mechanically scanned systems are the simple and low cost solution in microwave imaging. However, these systems are typically bulky and slow. This dissertation presents a design for a 2D switched imaging array that utilizes modulated scattering techniques for spatial multiplexing of the signal. The system was designed to be compact, coherent, possessing high dynamic range, and capable of video frame rate imaging. Various aspects of the system design were optimized to achieve the design objectives. The 2D imaging system as designed and described in this dissertation utilized PIN diode loaded resonant elliptical slot antennas as array elements. The slot antennas allow for incorporating the switching into the antennas thus reducing the cost and size of the array. Furthermore, these slots are integrated in a simple low loss waveguide network. Moreover, the sensitivity and dynamic range of this system is improved by utilizing a custom designed heterodyne receiver and matched filter. This dissertation also presents an analysis on the properties of this system. The performance of the multiplexing scheme, the noise floor and the dynamic range of the receivers are investigated. Furthermore, sources of errors such as mutual coupling and array response dispersion are also investigated. Finally, utilizing this imaging system for various applications such as 2D electric field mapping, scatterer localization, and nondestructive imaging is demonstrated --Abstract, Page iii