An Overview of Recent Development of the Gap-Waveguide Technology for mmWave and Sub-THz Applications

The millimeter-wave (mmWave) and sub-terahertz (sub-THz) bands have received much attention in recent years for wireless communication and high-resolution imaging radar applications. The objective of this paper is to provide an overview of recent developments in the design and technical implementation of GW-based antenna systems and components. This paper begins by comparing the GW-transmission line to other widely used transmission lines for the mmWave and sub-THz bands. Furthermore, the basic operating principle and possible implementation technique of the GW-technology are briefly discussed. In addition, various antennas and passive components have been developed based on the GW-technology. Despite its advantages in controlling electromagnetic wave propagation, it is also widely used for the packaging of electronic components such as transceivers and power amplifiers. This article also provided an overview of the current manufacturing technologies that are commonly used for the fabrication of GW-components. Finally, the practical applications and industry interest in GW technology developments for mmWave and sub-THz applications have been scrutinized.Funding Agencies|European Union - Marie Sklodowska-Curie [766231WAVECOMBEH2020-MSCA-ITN-2017]</p

Millimeter-wave Contactless Waveguide Joints and Compact OMT Based on Gap Waveguide Technology

Amongst the contemporary gap waveguide structures, both ridge gap waveguide (RGW) and groove gap waveguide (GGWG) display low losses and are resistant to signal leakage without the requirement of electrical contacts. In both scenarios, the concept is to allow the wave propagation through the guiding part and eliminating signal leakage in all other directions. Since, at present, millimeter-wave (mm-wave) has gained attention due to its versatile usability at high-frequency applications, it is quite obligatory to develop components with superior electrical features, like high stability, wider bandwidth, as well as high power handling capability at that frequency range. Considering the stated advantages, the proposed devices in this research work emphases on the mm-wave application that are mainly accountable for connecting standard waveguides and feeding antenna systems. The research work can be summarized in three segments. The first segment aims at designing waveguide adaptors based on the gap waveguide technology that do not necessarily require perfect electrical contact. The contact-free adaptor has been designed for both standard rectangular and circular waveguides covering multiple mm-wave frequency bands within 50- 110 GHz. Additionally, while designing the adaptor, surface roughness has been considered to achieve the response of the structure close enough to the practical case. The same adapter can also be used with different standard waveguide dimensions operating within 50-110 GHz by changing the adapter’s waveguide parameters. The proposed contact-free adaptor exhibits an excellent return loss and insertion loss of better than 20 dB and 0.3 dB, respectively, for both standard circular and rectangular waveguides, regardless of a smooth or uneven surface. The second segment focuses on a contact-free flangeless pipe connection for both circular and rectangular standard waveguides, covering multiple frequency bands amid 50 and 110 GHz. The contactless, low-loss, flange-free, and pluggable contact aims at joining two slightly modified standard waveguides, along with a 60% downscaling of the recommended structure compared to the traditional UG-387/U waveguide flange, hence demonstrating a reflection coefficient better than -20 dB in each scenario. In addition, the third segment is introducing microwave devices that can combine and separate two propagating polarizations, such as orthomode transducers (OMT). Aiming for high power applications with compact structure, the proposed configuration introduces a new design procedure of combining the ridge gap and groove gap waveguides for the OMTs, validating an acceptable matching level of better than -18 dB along with isolation higher than 70 dB. Finally, some valuable recommendations as an extension of this research work are suggested in the final chapter

Analysis and design of new electronically reconfigurable periodic leaky-wave antennas

[SPA] El principal objetivo de la tesis es el estudio de nuevas tecnologías en el campo de las antenas reconfigurables. En particular, la tesis se centra en explorar y explotar el potencial que presentan un tipo de antenas denominadas como ¿Antenas basadas en Modos de Fuga¿ para controlar electrónicamente su diagrama de radiación. La tesis desarrolla el análisis, diseño y fabricación de tres novedosas antenas basadas en modos de fuga capaces de variar mediante unas pocas señales de control y de forma continua su ángulo de apuntamiento. El mecanismo de reconfiguración electrónica principalmente se basa en el control de la dispersión de los modos de fuga excitados en dichas estructuras, mediante un control electrónico introducido empleando estructuras periódicas resonantes combinadas con elementos activos tales como diodos varactores. La tesis demuestra claramente la utilidad de estas antenas en el campo de la reconfiguración electrónica, proponiendo estas nuevas estructuras como alternativas a otras soluciones más clásicas (como antenas en array de fase reconfigurables o reflectores parabólicos mecánicamente re-orientables mecánicamente) y otras de actualidad (como reflectarrays, transmitarrays, antenas metamateriales o antenas pixeladas), las cuales todas ellas presentan otros problemas en términos de coste, complejidad de diseño o limitaciones de escalabilidad en frecuencia, aportando así esta tesis novedosos conceptos de reconfiguración electrónica.[ENG] The thesis aims the design of novel reconfigurable antennas with electronic beam-scanning. In particular, the antennas analyzed are known as Fabry-Perot Antennas (FPA) and are currently of high interest in the scientific community because of their high-directivity, low-profile and structure simplicity, what allow them to be an interesting alternative to other technologies (e.g. parabolic reflectors, phased arrays, etc.) which require of complex power distribution networks, bulky external sources or costly techniques to achieve reconfigurable capabilities. In this thesis, the integration of active components, such as varactor diodes, with FPRA structures, is exploited to achieve electronic control of their aperture illumination, which in turn results in the electronic steering of the radiation-pattern main beam. A modal analysis based on the leaky-wave theory has allowed to understand and predict the behavior of these structures. An equivalent circuit model was developed to design and optimize the dimensions of theses complex structures, saving computational cost and time. The antennas are based on the control of the frequency dispersion response and the electromagnetic band-gap (EBG) properties of periodic structures, employing specially designed Frequency-Selective Surfaces (FSS) loaded with varactor diodes. Three novel antenna prototypes were manufactured to demonstrate electronic steering capability operating at 5.5GHz. Continuous scanning in elevation (1D scanning) and also in elevation and azimuth simultaneously (2D scanning) have been achieved employing just a few control signals (between 1 and 4 signals). The antenna structures have been implemented in a low-cost technology based on parallel plate waveguides and printed circuit boards which have allowed to design antennas with a reduced profile. Theoretical, simulated and experimental results are shown for each prototype to demonstrate the concepts. Also, some future lines related to novel planar reconfigurable antennas in development are also outlined. One of the main potential advantages of the reconfiguring principles presented for future applications is their frequency scalability. This would allow to apply these concepts to other technologies, such as MEMS or graphene, to build new reconfigurable antennas able to operate at higher frequency bands (e.g. mm-bands) for future applications.Universidad Politécnica de Cartagen

Reconfigurable and Tunable Metamaterials: A Review of the Theory and Applications

Metamaterials are being applied to the development and construction of many new devices throughout the electromagnetic spectrum. Limitations posed by the metamaterial operational bandwidth and losses can be effectively mitigated through the incorporation of tunable elements into the metamaterial devices. There are a wide range of approaches that have been advanced in the literature for adding reconfiguration to metamaterial devices all the way from the RF through the optical regimes, but some techniques are useful only for certain wavelength bands. A range of tuning techniques span from active circuit elements introduced into the resonant conductive metamaterial geometries to constituent materials that change electromagnetic properties under specific environmental stimuli. This paper presents a survey of the development of reconfigurable and tunable metamaterial technology as well as of the applications where such capabilities are valuable

Terahertz Patch Antenna Microcavity Lasers with Integrated Beam Control

Terahertz (THz) refers to the region of the electromagnetic spectrum that lies in between the infrared and microwaves. This frequency range possesses great potential to host several applications in wide-ranging fields, such as wireless communications, astronomy, non-invasive imaging and security scanning. However, despite sustained progress over the past decade, THz technology has not yet reached the level of maturity and flexibility of the neighboring radio frequency (RF) and optical range. One missing key aspect is the ability to integrate advanced beam control functionalities within a monolithic platform. A promising approach to achieve this goal is to combine within a single device two features of the neighboring ranges: optical microcavities, that can sustain efficient lasing operation; and antenna arrays, providing a high level of beam control. In this thesis, we investigate via simulations fabrication and characterization the emission properties of arrays of patch antenna-coupled microcavities embedding quantum cascade active regions. The geometrical configuration of the array allows independent and simultaneous tuning of the losses governing the microcavities as well as beam shaping by constructive interference in the far-field. We show that optimized arrays emit THz with unprecedented low beam divergence and robust lasing in single frequency and spatial mode. Additionally, we demonstrate polarization functionalization by coupling the patch antenna microcavities with plasmonic wires. This feature introduces an additional degree of freedom to adjust the relative emission from the cross-polarized modes of the patch, allowing the device to radiate with any coherent polarization state from linear to circular. Finally, we discuss how this design can further enable other advanced functionalities such as active beam steering and control of THz non-linearities. The successful implementation of integrated advanced functionalities and sources on-a-chip demonstrates the ability of our platform to replicate in the THz range the beam control concepts used in the RF and optics, thus paving the way towards establishing a mature technology in this range of the electromagnetic spectrum.Okinawa Institute of Science and Technology Graduate Universit

Static and reconfigurable devices for near-field and far-field terahertz applications

The terahertz frequency electromagnetic radiation has gathered a growing interest from the scientific and technological communities in the last 30 years, due to its capability to penetrate common materials, such as paper, fabrics, or some plastics and offer information on a length scale between 100 µm and 1 mm. Moreover, terahertz radiation can be employed for wireless communications, because it is able to sustain terabit-per-second wireless links, opening to the possibility of a new generation of data networks. However, the terahertz band is a challenging range of the electromagnetic spectrum in terms of technological development and it falls amidst the microwave and optical techniques. Even though this so-called “terahertz gap” is progressively narrowing, the demand of efficient terahertz sources and detectors, as well as passive components for the management of terahertz radiation, is still high. In fact, novel strategies are currently under investigation, aiming at improving the performance of terahertz devices and, at the same time, at reducing their structure complexity and fabrication costs. In this PhD work, two classes of devices are studied, one for near-field focusing and one for far-field radiation with high directivity. Some solutions for their practical implementation are presented. The first class encompasses several configurations of diffractive lenses for focusing terahertz radiation. A configuration for a terahertz diffractive lens is proposed, numerically optimized, and experimentally evaluated. It shows a better resolution than a standard configuration. Moreover, this lens is investigated with regard to the possibility to develop terahertz diffractive lenses with a tunable focal length by means of an electro-optical control. Preliminary numerical data present a dual-focus capability at terahertz frequencies. The second class encompasses advanced radiating systems for controlling the far-field radiating features at terahertz frequencies. These are designed by means of the formalism of leaky-wave theory. Specifically, the use of an electro-optical material is considered for the design of a leaky-wave antenna operating in the terahertz range, achieving very promising results in terms of reconfigurability, efficiency, and radiating capabilities. Furthermore, different metasurface topologies are studied. Their analytical and numerical investigation reveals a high directivity in radiating performance. Directions for the fabrication and experimental test at terahertz frequencies of the proposed radiating structures are addressed

Design and analysis of miniaturized substrate integrated waveguide reconfigurable filters for mm-wave applications.

Doctoral Degree. University of KwaZulu-Natal, Durban.Microwave filters are an integral part of communication systems. With the advent of new technologies, microwave devices, such as filters, need to have superior performance in terms of power handling, selectivity, size, insertion loss etc. During the past decade, many applications have been added to the communication networks, resulting in communication systems having to operate at high frequencies in the region of THz to achieve the stringent bandwidth requirements. To achieve the requirements of the modern communication system, tunability and reconfigurability have become fundamental requirements to reduce the footprint of communication devices. However, the communication systems that are more prevalent such as planar circuits have either a large footprint or are not able to handle large amounts of power due to radiation leakage. In this thesis, Substrate Integrated Waveguide (SIW) technology has been employed. The SIW has the same properties as the conventional rectangular waveguide; hence it benefits from the high quality (Q) factor and can handle large powers with small radiation loss. The Half-mode (HMSIW), Quarter-mode (QMSIW), and Eighth-mode (EMSIW) cavity resonators have been designed and used for the miniaturization of the microwave filters. The coupling matrix method was used to implement a filter that uses cross-coupled EMSIW and HMSIW cavity resonators to improve the selectivity of the filter. Balanced circuit techniques have been used to design the circuits that preserve communication systems integrity whereby the Common Mode (CM) signal was suppressed using Deformed Ground Structure (DGS) and a center conductor patch with meandered line. For the designed dual-band filter, the common mode signal was suppressed to -90 dB and - 40 dB for the first and second passband, respectively. The insertion loss observed is 2.8 dB and 1.6 dB for the first and second passband, respectively. For tunability of the filter, a dual-band filter utilizing triangular HMSIW resonators has been designed and reconfigurability is achieved by perturbing the substrate permittivity by dielectric rods. The dielectric rods’ permittivity was changed to achieve tunability in the first instance, and then the rods’ diameter changed in the second instance. For the lowerband, frequency is tunable from 8.1 GHz to 9.15 GHz, while the upper band is tuned from 14.61 GHz to 16.10 GHz. A second order SIW filter with a two layer substrate was then designed to operate in the THz region. For reconfigurability, Graphene was sandwiched between the Silicon Di-Oxide substrate and the top gold plate of the filter, and the chemical potential of Graphene was then varied by applying a dc bias voltage. With a change in dc voltage the chemical potential of Graphene changes accordingly. From the results, a chemical potential change of 0.1 eV to 0.6 eV brings about a frequency change from 1.289 THz to 1.297 THz

Micro/Nano Structures and Systems

Micro/Nano Structures and Systems: Analysis, Design, Manufacturing, and Reliability is a comprehensive guide that explores the various aspects of micro- and nanostructures and systems. From analysis and design to manufacturing and reliability, this reprint provides a thorough understanding of the latest methods and techniques used in the field. With an emphasis on modern computational and analytical methods and their integration with experimental techniques, this reprint is an invaluable resource for researchers and engineers working in the field of micro- and nanosystems, including micromachines, additive manufacturing at the microscale, micro/nano-electromechanical systems, and more. Written by leading experts in the field, this reprint offers a complete understanding of the physical and mechanical behavior of micro- and nanostructures, making it an essential reference for professionals in this field

An investigation of nanoscale materials and their incorporation in patch antenna for high frequency applications

The rapid development in the polymer-based electronic contribute a strong determination for using these materials as substitute to the high-cost materials commonly used as medium substrate in the fabrication of Microstrip Patch Antenna (MPA). Antenna technology can strongly gain from the utilisation of low-cost, flexible, light weight with suitable fabrication techniques. The uniqueness of this work is the use of variety of common but unexplored different polymer materials such as Polyethylene (PE), Polypropylene (PP), Polyvinyl chloride, (PVC) Polystyrene (PS), Polystyrene fibre (PSF) as the substrates for the design and fabrication of different MPAs for communication and sensing applications in millimetre wave (MMW)region. Electrospinning (ES) technique is used to reconstruct PS and produced PSF material of low dielectric constant. A co-solvent vehicle(comprising 50:50 ratio) of Dichloromethane (DCM) and acetone was utilised with processing condition of solution infusion flow-rate of 60μL/min and an applied voltage of 12± kV yielded rigid PSF substrates. The PSF Produced has complex permittivity of 1.36±5% and a loss tangent of 2.4E-04±4.8E-04 which was measured using Spilt-Post Dielectric Resonators (SPDR) technique at National Physics Laboratory, Teddington, London. A diamond-shaped MPAs on RT Duriod material were simulated and fabricated using photo-lithography for different inner lengths to work in the frequencies range from (1-10 GHz). The resonant frequency is approximated as a function of inner length L1 in the form of a polynomial equation. The fabricated diamond-shaped MPA more compact (physical geometry) as compared with a traditional monopole antenna. This MPAs experimentally measured and have a good agreement with the simulated results. The coplanar waveguide (CPW) diamond-shaped MPA working in the MMW region was designed and fabricated with polymer materials as substrates using thermal evaporation technique and the RF measurement was carried out using Vector Network Analyser (VNA). The resonant frequencies of the CPW diamond shaped MPAs for (PE, PP, PVC, PS and PSF) were found to be 67.5 GHz, 72.36 GHz, 62.41 GHz, 63.25 GHz and 80.58 GHz, respectively. The antenna fabricated on PSF were resonating at higher frequency when compared to the other polymers materials. In adding an air-bridge to the CPW diamond-shaped MPA the resonating frequency increased from ≈55 GHz to≈ 62 GHz. Three different shaped nano-patch antennas (Diamond shaped, diamond shaped array and T-shaped) have been designed, simulated and fabricated on Silicon substrate with DLC deposition using focused Ion Beam (FIB) technique, these antennas were found to resonate at 1.42 THz with (-19 dB return loss), 2.42 THz with (-14 dB return loss) and 1.3 THz with (-45 dB return loss) respectively

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