124 research outputs found
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Architectures, Antennas and Circuits for Millimeter-wave Wireless Full-Duplex Applications
Demand for wireless network capacity keeps growing exponentially every year, as a result a 1000-fold increase in data traffic is projected over the next 10 years in the context of 5G wireless networks. Solutions for delivering the 1000-fold increase in capacity fall into three main categories: deploying smaller cells, allocating more spectrum and improving spectral efficiency of wireless systems. Smaller cells at RF frequencies (1-6GHz) are unlikely to deliver the demanded capacity increase. On the other hand, millimeter-wave spectrum (frequencies over 24GHz) offers wider, multi-GHz channel bandwidths, and therefore has gained significant research interest as one of the most promising solutions to address the data traffic demands of 5G.
Another disruptive technology is full-duplex which breaks a century-old assumption in wireless communication, by simultaneous transmission and reception on the same frequency channel. In doing so, full-duplex offers many benefits for wireless networks, including an immediate spectral efficiency improvement in the physical layer. Although FD promises great benefits, self-interference from the transmitter to its own receiver poses a fundamental challenge. The self-interference can be more than a billion times stronger than the desired signal and must be suppressed below the receiver noise floor. In recent years, there has been some research efforts on fully-integrated full-duplex RF transceivers, but mm-wave fully-integrated full-duplex systems, are still in their infancy.
This dissertation presents novel architectures, antenna and circuit techniques to merge two exciting technologies, mm-wave and full-duplex, which can potentially offer the dual benefits of wide bandwidths and improved spectral efficiency. To this end, two different antenna interfaces, namely a wideband reconfigurable T/R antenna pair with polarization-based antenna cancellation and an mm-wave fully-integrated magnetic-free non-reciprocal circulator, are presented. The polarization-based antenna cancellation is employed in conjunction with the RF and digital cancellation to design a 60GHz full-duplex 45nm SOI CMOS transceiver with nearly 80dB self-interference suppression. The concepts and prototypes presented in this dissertation have also profound implications for emerging applications such as vehicular radars, 5G small-cell base-stations and virtual reality
Integrated Circuit and Antenna Technology for Millimeter-wave Phased Array Radio Front-end
Ever growing demands for higher data rate and bandwidth are pushing extremely high data rate wireless applications to millimeter-wave band (30-300GHz), where sufficient bandwidth is available and high data rate wireless can be achieved without using complex modulation schemes. In addition to the communication applications, millimeter-wave band has enabled novel short range and long range radar sensors for automotive as well as high resolution imaging systems for medical and security. Small size, high gain antennas, unlicensed and worldwide availability of released bands for communication and a number of other applications are other advantages of the millimeter-wave band.
The major obstacle for the wide deployment of commercial wireless and radar systems in this frequency range is the high cost and bulky nature of existing GaAs- and InP-based solutions. In recent years, with the rapid scaling and development of the silicon-based integrated circuit technologies such as CMOS and SiGe, low cost technologies have shown acceptable millimeter-wave performance, which can enable highly integrated millimeter-wave radio devices and reduce the cost significantly. Furthermore, at this range of frequencies, on-chip antenna becomes feasible and can be considered as an attractive solution that can further reduce the cost and complexity of the radio package.
The propagation channel challenges for the realization of low cost and reliable silicon-based communication devices at millimeter-wave band are severe path loss as well as shadowing loss of human body. Silicon technology challenges are low-Q passive components, low breakdown voltage of active devices, and low efficiency of on-chip antennas.
The main objective of this thesis is to investigate and to develop antenna and front-end for cost-effective silicon based millimeter-wave phased array radio architectures that can address above challenges for short range, high data rate wireless communication as well as radar applications. Although the proposed concepts and the results obtained in this research are general, as an important example, the application focus in this research is placed on the radio aspects of emerging 60 GHz communication system. For this particular but extremely important case, various aspects of the technology including standard, architecture, antenna options and indoor propagation channel at presence of a human body are studied.
On-chip dielectric resonator antenna as a radiation efficiency improvement technique for an on-chip antenna on low resistivity silicon is presented, developed and proved by measurement. Radiation efficiency of about 50% was measured which is a significant improvement in the radiation efficiency of on-chip antennas. Also as a further step, integration of the proposed high efficiency antenna with an amplifier in transmit and receive configurations at 30 GHz is successfully demonstrated. For the implementation of a low cost millimeter-wave array antenna, miniaturized, and efficient antenna structures in a new integrated passive device technology using high resistivity silicon are designed and developed.
Front-end circuit blocks such as variable gain LNA, continuous passive and active phase shifters are investigated, designed and developed for a 60GHz phased array radio in CMOS technology. Finally, two-element CMOS phased array front-ends based on passive and active phase shifting architectures are proposed, developed and compared
High Gain Antenna Array Design for 5G & MIMO Antenna Systems using Microstrip Ridge Gap Waveguide
The demand for high data rates and the unavailability of low-frequency bands have driven the need to explore and develop millimeter-wave (mm-wave) frequency bands. Indeed, the development of mm-wave frequencies has led to smaller radio frequency (RF) components and more compact profiles, creating more design constraints and challenges. Millimeter-wave technologies are the best-suited candidates that meet the requirements of 5G standards; specifically, for indoor communication, which requires higher gain and more directive beams. Gap waveguide technologies can be used to design high-gain antenna arrays and multiple input multiple output antenna systems (MIMO).
In this thesis, we are mainly focusing on Microstrip Ridge Gap Waveguide (MRGW) to design the antenna array systems for the 60 GHz band. Therefore, it is necessary to facilitate the design procedures and propose new design techniques. Here, we propose new design techniques for a large antenna array system using MRGW. The work of this thesis can be divided into two parts. Firstly, developing an efficient modeling and design tool for the MRGW to facilitate the design process. Recently, the use of MRGW has increased due to the need for self-packaged and low loss structures for millimeter-wave applications. The MRGW consists of a grounded textured surface, which is representing an artificial magnetic conductor (AMC) surface. The AMC surface is loaded with a thin low dielectric constant substrate with a printed strip topped with another air-filled or dielectric-filled substrate in which the wave propagates between the strip and the conducting plate covering such a substrate.
Currently, full-wave and optimization tools are usually used to design the MRGW structure, which makes the design slow and computationally expensive. Thus, an efficient modeling and design tool for the MRGW is proposed. Empirical expressions are developed for different MRGW parameters to provide the effective dielectric constant, characteristic impedance, and the dispersion effect. The expressions are verified with the full-wave solution. The results show the potential of the proposed approach in modeling and designing the MRGW structure. Secondly, an efficient procedure to design a large finite planar array and its corporate feeding network is presented. The procedure is verified by an 8 × 8 and 16 ×16 array of magneto-electric (ME) dipoles fed by a network of MRGW. The procedure is based on designing the corporate feeding network by replacing the elements ports with the corresponding effective input impedance of each element that accounts for the mutual coupling between the antenna elements. In addition, the far-field characteristics of the array parameters such as the directivity, gain, and radiation patterns are predicted using pattern multiplication, including the mutual coupling effects. The results are verified with the full-wave numerical solution.
The procedure requires limited resources and speed up the design cycle. The use of the MRGW helps in having the feeding network lines to be titer than using the ridge gap technology. Thus, allowing the distance between the radiating elements becomes smaller than one wavelength to avoid grating lobes. In addition, to avoid undesired bends and very tight lines that cause undesired interaction between the lines, unique power dividers are designed. Furthermore, a transition from waveguide WR-15 to the MRGW is proposed to feed two halves of the array antenna perfect out of phase at all frequencies and rotating each half to form a mirrored array that better radiation pattern symmetry and low cross-polarization. Then, this procedure is implemented to design a circularly polarized antenna array with excellent performance. To further enhance the antenna, gain, and reduce the number of elements, a superstrate dielectric lens with the proper parameters is added. Study of a 4 × 4 MIMO system is studied, where each antenna is a sub-array to achieve the high gain requirements.
Finally, A low-profile, compact, and high-efficiency monopulse array antenna has been presented. The monopulse is built based on a hybrid coupler that has a wideband response for the reflection and the transmission coefficients. Then the monopulse system is used to present a multiplexing antenna system for short-range in the near filed region wireless communication. The multiplexing system works as a MIMO system that has four independent channels. The performance of the system is evaluated through the simulation, which shows that it can be a promising candidate for the next wireless communication systems
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Wideband Microwave, Millimeter-Wave and Light-Wave Antennas
Wideband antennas are capable of maintaining consistent near- and far-field performance over wide bandwidths. With the rapid growth of information technologies and ever increasing needs for high data throughput, these antennas become increasingly important for modern communication systems. However, many challenges arise in the design of wideband antennas and their use in different regions of the frequency spectrum.
Majority of wideband antennas designed for commercial applications nowadays operate at microwave frequencies, for which low-cost and low-profile are often as important as antenna’s consistent electrical performance. This thesis first proposes a new feeding method to increase the bandwidth of the inherently narrowband patch antennas, the workhorse of modern communication industry. Compared with the previously published approaches, the proposed feeding technique delivers significantly increased impedance and far-field bandwidths, while maintains the antenna’s low-cost and low-profile properties. The associated challenges including radiation pattern degradation, mutual port couplings, and electrical sensitivity on structural variations are thoroughly discussed and carefully addressed.
Considering the congestion of lower microwave spectrum, modern wireless systems are often designed for millimeter-wave spectrum. Typically they require wideband millimeter-wave antennas capable of seamless, preferably monolithic integration with the system’s electronic circuitry. Recent advances in micro-electro-mechanical technologies have contributed to the development of micromachining processes capable of achieving many desired features of millimeter-wave systems. The second part of the thesis demonstrates millimeter-wave logperiodic dipole array (LPDA) antennas designed for and fabricated with a thick photolithography manufacturing process. It is shown for the first time that millimeter-wave LPDA antennas can be reliably achieved in the millimeter-wave region. It is also demonstrated that it is possible to monolithically integrate different devices within the LPDA antenna without impacting the antenna performance. For low-cost dual-polarized wideband antenna solutions, millimeter-wave planar log-periodic antennas fabricated using printed circuit board (PCB) process are also investigated as an alternative to the LPDA antennas.
Finally, wideband on-chip optical antennas are demonstrated for low-loss low-latency optical interconnects for the next generation microprocessor multi-core systems. Due to the high metallic loss at these frequencies, silicon-on-insulator based dielectric antennas are developed and over 50THz bandwidth is demonstrated. Based on the designed optical antennas, wideband optical signal hubs for wavelength-division-multiplexed (WDM) channel interconnects and data broadcast are developed. Theoretical study shows the proposed interconnect solution provides significantly increased power efficiency compared with the traditional electrical interconnect solution
Radio Channel Characterization for Future Wireless Networks and Applications
The new frontier of Above-6GHz bands is revolutionizing the field of
wireless telecommunications, requiring new radio channel models to support
the development of future Giga-bit-per-second systems. Recently, deterministic
ray-based models as Ray Tracing are catching on worldwide thanks to their
frequency-agility and reliable predictions. A modern 3D Ray Tracing developed
at University of Bologna has been indeed calibrated and used to investigate the
Above-6GHz radio channel properties. As starting point, an item-level electromagnetic
characterization of common items and materials has been achieved successfully
to obtain information about the complex permittivity, scattering diagrams and
even de-polarization effects, both utilizing Vector Spectrum Analyzer (at 7-15GHz)
and custom Channel Sounder (at 70GHz). Thus, a complete tuning of the Ray Tracing
has been completed for Above-6GHz frequencies. Then, 70GHz indoor doubledirectional
channel measurements have been performed in collaboration with TU
Ilmenau, in order to attain a multidimensional analysis of propagation mechanisms
in time and space, outlining the differences between Below- and Above-6GHz propagation.
Furthermore, multi-antenna systems, as Multiple-Input-Multiple-
Output (MIMO) and Beamforming have been taken into considerations, as strategic
technologies for Above-6GHz systems, focusing on their implementation, limits
and differences. Finally, complex system simulations of Space-Division-Multiple-
Access (SDMA) networks in indoor scenarios have been tested, to assess the capabilities
of Beamforming. In particular, efficient Beam Search and Tracking algorithms
have been proposed to assess the impact of interference on Multi-User Beamforming
at 70GHz and, also, novel Multi-Beam Beamforming schemes have been tested
at 60GHz to investigate diversity strategies to cope with NLOS link and Human
Blockage events. Moreover, the novel concept of Ray-Tracing-assisted Beamforming
has been outlined, showing that ray-based models represent today the promising
key tools to evaluate, design and enhance the future Above-6GHz multi-antenna
systems
Gigabit wireless connector and multibeam antenna : design and implementation using 60-GHz technology
60 GHz Wireless Propagation Channels: Characterization, Modeling and Evaluation
To be able to connect wirelessly to the internet is nowadays a part of everyday life and the number of wireless devices accessing wireless networks worldwide are increasing rapidly. However, with the increasing number of wireless devices and applications and the amount available bandwidth, spectrum shortage is an issue. A promising way to increase the amount of available spectrum is to utilize frequency bands in the mm-wave range of 30-300 GHz that previously have not been used for typical consumer applications. The 60 GHz band has been pointed out as a good candidate for short range, high data rate communications, as the amount of available bandwidth is at least 5 GHz worldwide, with most countries having 7 GHz of bandwidth available in this band. This large bandwidth is expected to allow for wireless communication with bit rates up to 7 Gbit/s, which can be compared to the typical WLAN systems of today that typically provide bit rates up to 0.6 Gbit/s. However, the performance of any wireless system is highly dependent on the properties and characteristics of the wireless propagation channel. This thesis focuses on indoor short range wireless propagation channels in the 60 GHz band and contains a collection of papers that characterizes, models and evaluates different aspects that are directly related to the propagation channel properties. Paper I investigates the directional properties of the indoor 60 GHz wireless radio channel based on a set of indoor measurements in a conference room. In the paper, the signal pathways and propagation mechanisms for the strongest paths are identified. The results show that first and second order interactions account for the major contribution of the received power. The results also show that finer structures, such as ceiling lamps, can be significant interacting objects. Paper II presents a cluster-based double-directional channel model for 60 GHz indoor multiple-input multiple-output (MIMO) systems. This paper is a direct continuation of the results in paper I. The model supports arbitrary antenna elements and array configurations and is validated against measurement data. The validation shows that the channel model is able to efficiently reproduce the statistical properties of the measured channels. The presented channel model is also compared with the 60 GHz channel models developed for the industry standards IEEE802.15.3c and IEEE802.11ad. Paper III characterizes the effect of shadowing due to humans and other objects. Measurements of the shadowing gain for human legs, metallic sheets, as well as metallic and plastic cylinders are presented. It is shown that the shadowing gain of these objects are fairly similar and that the shadowing due to the metal cylinder can be determined based on the geometrical theory of diffraction. Next, the shadowing due to a water-filled human body phantom is compared with the shadowing due to real humans. The results show that the water-filled phantom has shadowing properties similar to those of humans and is therefore suitable for use in 60 GHz human body shadowing measurements. Paper IV presents a novel way of estimating the cluster decay and fading. Previously, the cluster decay has usually been determined by performing a simple linear regression, without considering the effects of the noise floor and cluster fading. The paper presents an estimation method which takes these effects into account and jointly estimates both the cluster decay and cluster fading. It is shown that this estimation method can greatly improve the estimated parameters. Paper V evaluates the capacity improvement capability of spatial multiplexing and beamforming techniques for 60 GHz systems in an indoor environment. In this paper, beamforming refers to conventional gain focusing in the direction of the strongest propagation path. The paper uses a capacity metric that only depends on the multi-path richness of the propagation channel and the antenna aperture size. In the paper, it is shown that, when the link budget is limited due to electrically small antennas and long Tx-Rx separation distances, beamforming approximates the capacity of spatial multiplexing. However, spatial multiplexing is a worthwhile option when Rx SNR is favorable and a higher peak data rate is required. Paper VI describes different methods for the clustering of wireless multi-path components. In the literature, the clustering method that is predominantly used is the K-means algorithm, or a power-weighted version of K-means, called K-power means. In this paper, we point out that K-means is a special case of a Gaussian mixture model (GMM). The paper presents a clustering method based on a GMM. This method is able to handle arbitrary cluster spreads in the different dimensions better than the K-means algorithm. A power-weighted version of the GMM is also presented. In addition to this, a mixture model based on asymmetric Laplace distributions is also presented, with and without power-weighting. Paper VII is based on channel measurements in a small and a large room, where the Tx and Rx arrays have dual polarized elements. Using these measurements, the cross-polarization ratio (XPR) of the multi-path components are characterized. This gives valuable information on how the MPCs are affected by the propagation channel. A statistical description of the XPR is also needed for the development of a propagation channel model that supports polarization. The paper also investigates the eigenvalue spreads for single and dual polarized elements. Furthermore, the measurements include LOS and NLOS measurement, where the NLOS scenarios include water-filled human presented in paper III. The results show that the capacity can be greatly improved if dual-polarized elements are used, and that the XPR values are in general higher compared to lower frequencies
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