Bandwidth reconfigurable metamaterial arrays

Metamaterial structures provide innovative ways to manipulate electromagnetic wave responses to realize new applications. This paper presents a conformal wideband metamaterial array that achieves as much as 10: 1 continuous bandwidth. This was done by using interelement coupling to concurrently achieve significant wave slow-down and cancel the inductance stemming from the ground plane. The corresponding equivalent circuit of the resulting array is the same as that of classic metamaterial structures. In this paper, we present a wideband Marchand-type balun with validation measurements demonstrating the metamaterial (MTM) array\u27s bandwidth from 280 MHz to 2800 MHz. Bandwidth reconfiguration of this class of array is then demonstrated achieving a variety of band-pass or band-rejection responses within its original bandwidth. In contrast with previous bandwidth and frequency response reconfigurations, our approach does not change the aperture\u27s or ground plane\u27s geometry, nor does it introduce external filtering structures. Instead, the new responses are realized by making simple circuit changes into the balanced feed integrated with the wideband MTM array. A variety of circuit changes can be employed using MEMS switches or variable lumped loads within the feed and 5 example band-pass and band-rejection responses are presented. These demonstrate the potential of the MTM array\u27s reconfiguration to address a variety of responses. © 2014 Nathanael J. Smith et al

Challenges in Clock Synchronization for On-Site Coding Digital Beamformer

Typical radio frequency (RF) digital beamformers can be highly complex. In addition to a suitable antenna array, they require numerous receiver chains, demodulators, data converter arrays, and digital signal processors. To recover and reconstruct the received signal, synchronization is required since the analog-to-digital converters (ADCs), digital-to-analog converters (DACs), field programmable gate arrays (FPGAS), and local oscillators are all clocked at different frequencies. In this article, we present a clock synchronization topology for a multichannel on-site coding receiver (OSCR) using the FPGA as a master clock to drive all RF blocks. This approach reduces synchronization errors by a factor of 8, when compared to conventional digital beamformer

Compact Metamaterials Induced Circuits and Functional Devices

In recent years, we have witnessed a rapid expansion of using metamaterials to manipulate light or electromagnetic (EM) wave in a subwavelength scale. Specially, metamaterials have a strict limitation on element dimension from effective medium theory with respect to photonic crystals and other planar structures such as frequency selective surface (FSS). In this chapter, we review our effort in exploring physics and working mechanisms for element miniaturization along with the resulting effects on element EM response. Based on these results, we afford some guidelines on how to design and employ these compact meta-atoms in engineering functional devices with high performances. We found that some specific types of planar fractal or meandered structures are particularly suitable to achieve element miniaturization. In what follows, we review our effort in Section 1 to explore novel theory and hybrid method in designing broadband and dual band planar devices. By using single or double such compact composite right-/left-handed (CRLH) atom, we show that many microwave/RF circuits, i.e., balun, rat-race coupler, power divider and diplexer, can be further reduced while without inducing much transmission loss from two perspectives of lumped and distributed CRLH TLs. In Section 2, we show that a more compact LH atom can be engineered by combining a fractal ring and a meandered thin line. Numerical and experimental results demonstrate that a subwavelength focusing is achieved in terms of smooth outgoing field and higher imaging resolution. Section 3 is devoted to a clocking device from the new concept of superscatterer illusions. To realize the required material parameters, we propose a new mechanism by combining both electric and magnetic particles in a composite meta-atom. Such deep subwavelength particles enable exact manipulation of material parameters and thus facilitate desirable illusion performances of a proof-of-concept sample constructed by 6408 gradually varying meta-atoms. Finally, we summarize our results in the last section

Analysis and design of enhanced planar devices using multiconductor transmission lines with interconnected alternate lines

Novel capabilities and applications of multiconductor transmission lines with interconnected alternate lines have been analyzed in this work. The interconnections among alternate strips broaden the operating frequency band by eliminating undesired resonances and allow the use of simplified analytical models. Phase shifters, baluns, reconfigurable systems for the characterization of balanced circuits, ultra-wideband differential bandpass filters and quasi-elliptic bandpass filters have been proposed and demonstrated. For all these circuits a systematic design procedure have been derived and validated by means of experimental work. The excellent agreement between the measurements and the predicted results validates the proposed procedures as reliable and quick design techniques

Bandwidth Reconfigurable Metamaterial Arrays

Metamaterial structures provide innovative ways to manipulate electromagnetic wave responses to realize new applications. This paper presents a conformal wideband metamaterial array that achieves as much as 10 : 1 continuous bandwidth. This was done by using interelement coupling to concurrently achieve significant wave slow-down and cancel the inductance stemming from the ground plane. The corresponding equivalent circuit of the resulting array is the same as that of classic metamaterial structures. In this paper, we present a wideband Marchand-type balun with validation measurements demonstrating the metamaterial (MTM) array’s bandwidth from 280 MHz to 2800 MHz. Bandwidth reconfiguration of this class of array is then demonstrated achieving a variety of band-pass or band-rejection responses within its original bandwidth. In contrast with previous bandwidth and frequency response reconfigurations, our approach does not change the aperture’s or ground plane’s geometry, nor does it introduce external filtering structures. Instead, the new responses are realized by making simple circuit changes into the balanced feed integrated with the wideband MTM array. A variety of circuit changes can be employed using MEMS switches or variable lumped loads within the feed and 5 example band-pass and band-rejection responses are presented. These demonstrate the potential of the MTM array’s reconfiguration to address a variety of responses

Compact and broadband antenna system at UHF

The aim of this research was to study a novel, broadband, low cost, low profile and a high-medium gain antenna in the UHF band. This has been achieved through numerical modelling, theoretical investigation and physical measurements. In this study two commercially available antenna systems are investigated in order to compare and establish potential deficiencies in the UHF antenna systems. A number of disadvantages are resolved within a novel antenna system design. The parametric study is performed for each element of the novel antenna system in order to optimise its overall performance. The indoor and outdoor measurements have been carried out in house, in order to validate the predicted results. The novel antenna system is compared to the most popular and commercially available UHF antenna systems. The study demonstrates that the novel antenna system has clear advantages such as broadband, balanced, compact and low cost when compared to the commercial antenna designs studied here. The comparison of the manufacturers’ data to the measured results shows a good match, validating the outdoor measurements technique used in this research

Contribution to characterization techniques for practical metamaterials and microwave applications

Metamaterials (MTMs) are broadly defined as artificial composite materials specifically engineered to produce desired unusual electromagnetic properties not readily available in nature. The most interesting unusual property achievable with MTMs is probably negative refraction, which is achieved when both the permittivity and the permeability of a medium are negative. Such structures are also referred to as left-handed media (LHM). From the first evidences in the early 2000's showing that materials with a negative refractive index were indeed physically realizable, numerous entirely new devices or improvements of existing devices have been reported in the microwave and antenna fields. In this context, the objective of this thesis is to contribute to the development of new characterization techniques for practical implementations of MTMs, aiming at determining a set of relevant equivalent medium parameters describing the structure from a macroscopic point of view. For this purpose, analysis techniques were developed based on the theory of wave propagation in periodic structures, and tested on selected existing or entirely new MTM structures of the two main reported categories: arrays of resonant particles and loaded transmission lines. In the first part of the work, an improved retrieval procedure which allows the determination of equivalent dyadic permittivity and permeability of MTMs from reflection and transmission coefficients obtained for several incidences was developed and tested, thereby extending current techniques which only dealt with normal incidence. The main achievement obtained with this technique is the ability to evaluate to which extent a given MTM slab can be considered as an equivalent homogeneous medium obeying some specific constitutive relations. This technique was tested on various structures, including a novel highly isotropic artificial magnetic material which was shown to exhibit a negative permeability in the three dimensions. In a second step, MTMs based on the transmission line approach have been investigated. In this context, the theory of the so-called composite right/left-handed transmission line (CRLH TL) has been revisited, and several planar implementations of this structure in various technologies were designed and realized. Subsequently, a volumetric LHM obtained by layering several planar artificial TLs of the CRLH type was proposed and fully characterized. This volumetric structure was shown to support left-handed propagation over a quite large bandwidth, compared to other resonant LHM made of split-ring resonators and wires. We provided an extensive experimental assessment of potential applications of this structure as an exotic substrate for microstrip patch antennas. An important contribution here consisted in the assessment of the ability of such a volumetric structure based on the TL approach to behave as a material filling in this type of configurations. The next part presents an enhanced analysis technique for periodic structures which allows accurately characterizing MTMs exhibiting higher order coupling phenomena between successive cells. This technique also allows an accurate and complete description of more elaborated structures such as periodically loaded multiconductor TLs. The main idea of this technique is to model the periodic structure with an equivalent multiconductor TL, a model which provides all the parameters needed to describe the phase response (dispersion) and terminations (excitation and matching) of finite size periodic structures. In the last part, we introduced and analyzed a novel unit cell topology for the CRLH TL which employs a lattice network in place of the conventional ladder-type topology. This new CRLH TL was shown to exhibit a more wideband behaviour than its conventional counterpart, both in terms of impedance and phase. These performances were numerically and experimentally demonstrated on several practical implementations. The possibilities of using this unit cell to reduce the beam squinting in leaky-wave antennas and in series-fed arrays were highlighted. It is foreseen that this new CRLH TL can be potentially used to improve the performances of many of the well-known CRLH TL applications

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

Analysis and design of metamaterial-inspired microwave structures and antenna applications

Novel metamaterial and metamaterial-inspired structures and microwave/antenna applications thereof are proposed and studied in this thesis. Motivated by the challenge of extending the applicability of metamaterial structures into practical microwave solutions, the underlying objective of this thesis has been the design of low-cost, easily fabricated and deployable metamaterial-related devices and the development of computational tools for the analysis of those. For this purpose, metamaterials composed of tightly coupled resonators are chosen for the synthesis of artificial transmission lines and enabling antenna applications. Specifically, fully-printed double spiral resonators are employed as modular elements for the design of tightly coupled resonators arrays. After thoroughly investigating the properties of such resonators, they are used for the synthesis of artificial lines in either grounded or non-grounded configurations. In the first case, the supported backward waves are exploited for the design of microstrip-based filtering/diplexing devices and series-fed antenna arrays. In the second case, the effective properties of such structures are employed for the design of a novel class of self-resonant, low-profile folded monopoles, exhibiting low mutual coupling and robust radiating properties. Such monopoles are, in turn, used for the synthesis of different sub-wavelength antenna arrays, such as superdirective arrays. Finally, an in-home periodic FDTD-based computational tool is developed and optimized for the efficient and rigorous analysis of planar, metamaterial-based, high-gain antennas.EThOS - Electronic Theses Online ServiceGBUnited Kingdo