Construction of Green's functions of parallel plates with periodic texture with application to gap waveguides - A plane wave spectral domain approach

This study presents Green's functions of parallel-plate structures, where one plate has a smooth conducting surface and the other an artificial surface realised by a one-dimensional or two-dimensional periodic metamaterial-type texture. The purpose of the periodic texture is to provide cut-off of the lowest order parallel-plate modes, thereby forcing electromagnetic energy to follow conducting ridges or strips, that is, to form a gap waveguide as recently introduced. The Green's functions are constructed by using the appropriate homogenised ideal or asymptotic boundary conditions in the plane-wave spectral domain, thereby avoiding the complexity of the Floquet-mode expansions. In the special case of a single ridge or strip, an additional numerical search for propagation constants is needed and performed in order to satisfy the boundary condition on the considered ridge or strip in the spatial domain. The results reveal the dispersion characteristics of the quasi-transverse electromagnetic modes that propagate along the ridges or strips, including their lower and upper cut-off frequencies, as well as the theoretical decay of the modal field in the transverse cut-off direction. This lateral decay shows values of 50-100 dB per wavelength for realisable geometries, indicating that the gap waveguide modes are extremely confined. The analytical formulas for the location of the stopband of the lowest order parallel-plate modes obtained by small-argument approximation of the dispersion equation are also shown. To verify the proposed analysis approach, the results are compared with the results obtained with a general electromagnetic solver showing very good agreement

Exploring lean production in the flexible manufacturing systems environment: some tensions between features of advanced manufacturing technologies and new wave manufacturing strategies

Exploring lean production in the flexible manufacturing systems environment: some tensions between features of advanced manufacturing technologies and new wave manufacturing strategie

Ultra-High Q-Factor Silicon Resonator for High Frequency Oscillators

The thesis focuses on the investigation and characterisation of ultra-high Q-factor low loss Silicon resonators with transverse electric (TE)-like electromagnetic band-gap determined by two dimensional periodic structure made of a Silicon slab having a triangular lattice of air cylinders. A band-gap is observed where no energy is propagated through the slab, however engineering defects are created and optimised within the lattice producing resonant cavities and waveguides. The structure being excited with the fundamental TE10 mode can be coupled to external circuits via waveguides and its respective transitions in co-planar waveguide transmission line used to convey the millimetre-wave frequency signals. The ultimate goal is to investigate and characterise the promising low loss and high frequency Silicon resonators suitable for millimetre-wave communications such as used in low phase noise oscillator application and band pass filters. The results clearly show that electromagnetic band-gap structures or photonic crystals (PC) can be utilized for application in high frequency oscillators directly in fundamental mode with great benefits in obtaining ultra-high Q-factor and therefore low phase noise; and with better performance than alternative state-of-art technologies such as crystal oscillators in combination with frequency multiplication or frequency synthesis causing an increase in the overall phase noise by 20 log rule. By successfully demonstrating the experiment of using electromagnetic band-gap structures with oscillators, it is a great contribution towards the solution of the problem of high phase noise affecting high frequency oscillators operating at millimetre-wave band

Computational studies of the electromagnetic properties of metamaterials and applications

In this thesis computational studies on electromagnetic properties of metamaterials and applications are introduced. The studies include an introduction to the time-domain transmission line modelling (TLM) method and the fundamental scattering properties of metamaterials. The first major objective of the thesis is directed to predicting the resonant frequencies of some forms of cut-wire (CW) metamaterials by using approximate equivalent circuits. The second objective is the improvement of metamaterial simulation efficiency based on two approaches: a simulation method based on retrieved metamaterial electromagnetic properties and one based on digital filtering (DF) techniques. By using the DF techniques, metamaterials are effectively modelled and the simulation times are significantly reduced. The third objective is focused on studying CW metamaterial as potential absorbers by deliberately including conductive losses. The proposed CW metamaterials are found to exhibit customisable absorptance characteristics with arbitrary polarisation. This metamaterial absorber study includes an experimental validation

Low-Profile, Electrically Small, Huygens Source Antenna with Pattern-Reconfigurability That Covers the Entire Azimuthal Plane

© 1963-2012 IEEE. A pattern-reconfigurable, low-profile, efficient, electrically small, near-field resonant parasitic (NFRP), Huygens source antenna is presented. The design incorporates both electric and magnetic NFRP elements. The electric ones are made reconfigurable by the inclusion of a set of p-i-n diodes. By arranging these electric and magnetic NFRP elements properly, a set of three Huygens sources are attained, each covering a 120° sector. Pattern reconfigurability is obtained by switching the diodes on or off; it encompasses the entire 360° azimuth range. A prototype was fabricated and tested. The numerical and experimental studies are in good agreement. The experimental results indicate that in each of its instantaneous states at = 1.564$ GHz, the antenna provides uniform peak realized gains, front-to-back ratios, and radiation efficiencies, respectively, as high as 3.55 dBi, 17.5 dB, and 84.9%, even though it is electrically small: 0.92 , and low profile

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

Computational studies of the electromagnetic properties of metamaterials and applications

In this thesis computational studies on electromagnetic properties of metamaterials and applications are introduced. The studies include an introduction to the time-domain transmission line modelling (TLM) method and the fundamental scattering properties of metamaterials. The first major objective of the thesis is directed to predicting the resonant frequencies of some forms of cut-wire (CW) metamaterials by using approximate equivalent circuits. The second objective is the improvement of metamaterial simulation efficiency based on two approaches: a simulation method based on retrieved metamaterial electromagnetic properties and one based on digital filtering (DF) techniques. By using the DF techniques, metamaterials are effectively modelled and the simulation times are significantly reduced. The third objective is focused on studying CW metamaterial as potential absorbers by deliberately including conductive losses. The proposed CW metamaterials are found to exhibit customisable absorptance characteristics with arbitrary polarisation. This metamaterial absorber study includes an experimental validation

E-plane parallel coupled resonators for waveguide bandpass filter applications

High skirt selectivity and extended out-of-band rejection is a major challenge for the successful progress of in-line microwave filters. This thesis presents novel filter realizations with improved performance, compatible with the standard single thin all-metal insert in a split-block housing and therefore maintaining the low-cost fabrication characteristics. In addition, significant filter performance improvement is achieved. The synthesis procedure implemented for the filter concept consists of a few steps. Some preliminary steps are a rigorous characterization of a double-ridge coaxial waveguide, and the modelling of an equivalent circuit model for the parallel coupled ridge waveguide devised in the filter concept. From these elements, a full wave electromagnetic analysis shows that parallel-coupled asymmetric ridge waveguides produce strongly dispersive coupling which introduces a transmission zero. Later on this property is extended to parallel-coupled asymmetric ridge waveguide resonators, where it is demonstrated that it is possible to independently control the coupling coefficient and the frequency of the transmission zero. This allows the realization of pseudo-elliptic narrowband in-line bandpass filters in E-plane technology. A general synthesis procedure for high order filters is outlined and numerical and experimental results are presented for validation. The elements employed for the synthesis procedure of the bandpass prototypes are also applied to investigate structures suitable for different applications. In particular, stopband and dual stopband filters are presented with numerical and experimental results. Finally, the study of a microwave chemical/biochemical sensing device for the characterization and detection of cells in chemical substances and cells in solution in micro-litre volumes is also reported.Engineering and Physical Sciences Research Council(EPSRC

Directive antennas based on two-dimensional dielectric EBG crystals

The aim of this work is the design and analysis of novel antennas realised with electromagnetic bandgap (EBG) structures based on simple two-dimensional cylindrical, triangular and square lattices of dielectric rods. In particular, we focused our attention on designing antennas with high directivity and front-to-back-ratio (FTBR) on the azimuthal plane. Several EBG structures have been investigated, divided in two main categories: multilayer EBG structures with an angular defect window and EBG corner reflectors. The former are based on a feeding source excited within a cavity: fields at badgap frequencies are trapped inside the cavity and opening an angular defect window allows propagation in that privileged directions leading to directive radiation patterns. The latter are based on a source placed in front of an EBG corner reflector: at bandgap frequencies, the excited fields are reflected toward the corner aperture (in a similar fashion to metallic corners of analogous dimensions) enhancing radiation patterns’ directivity. The analysed structures have been also modified to host multiple sources to create multiple-feed antenna structures with the ability of rotating the radiation patterns on the azimuthal plane. Antennas have been modelled using an in-house developed Finite-Difference Time- Domain solver and the commercial Finite Element Method solver Ansoft HFSS, focusing on structures designed to operate in the X-band frequency region (8.2GHz-12.4GHz) in order to take advantage of the available equipment and facilities at Heriot-Watt University for prototypes testing. The proposed structures can be nevertheless scaled up or down in size in order to respectively scale down or up of the same factor the frequency of operation. The main achievements of the analysed multilayer EBG structures and corner EBG reflectors are the large impedance bandwidth (greater than 30%) with stable radiation patterns within, high gain (>12dBi) and high FTBR (greater than 25dB) accomplished using EBG structures made with a small number (10-20) of low-loss ceramic rods arranged in very simple two-dimensional crystals. EBG corner reflectors have been also found basically equivalent (at badgap frequencies) to metal reflectors in terms of achieved gain and radiation patterns, suggesting them as possible substitutes for high frequencies applications where dielectric losses would be smaller than metal losses

A Planar Dual Notched Band Vivaldi Antenna for Wireless Communication Applications

With the aim of realizing a Vivaldi Antenna (VA) with stop bands for wireless communication applications, this paper introduces a novel, uncomplicated, easily fabricated, and compact planar VA featuring two distinctive rejected&nbsp;frequency bands. The designed VA is engraved onto an FR4-epoxy substrate, measuring 0.4243λ0×0.4296λ0&nbsp;×0.01315λ0&nbsp;at 2.63 GHz. The integration of dual notched band functionality is ingeniously achieved through the implementation&nbsp;of a simple additional strip and a U-formed slit. A physical prototype of the VA was successfully constructed&nbsp;and meticulously measured with the R&amp;S®ZNB Vector Network Analyser. The measured impedance bandwidth&nbsp;demonstrates that the realised VA operates from 2.63 GHz to beyond 12 GHz while effectively excluding two&nbsp;bands: 3.46-4.16 GHz (18.37 %) and 5.32-6.5 GHz (19.97 %). Simulated results indicate that the designed VA can&nbsp;provide stable unidirectional radiation patterns, reasonable realized gain, and acceptable radiation efficiency across&nbsp;its operating ranges, with notable drops observed at the two notched bands. As a result, these findings highlight&nbsp;the practical value of the designed VA for wireless communication applications, particularly in scenarios where the&nbsp;integration of filtering structures in antennas becomes essential to prevent interference with co-existing systems. The&nbsp;presented VA opens new avenues for enhancing wireless communication performance, catering to the increasing&nbsp;demand for reliable and interference-resistant solutions