Developing Novel 3D Antennas Using Advanced Additive Manufacturing Technology

In today’s world of wireless communication systems, antenna engineering is rapidly advancing as the wireless services continue to expand in support of emerging commercial applications. Antennas play a key role in the performance of advanced transceiver systems where they serve to convert electric power to electromagnetic waves and vice versa. Researchers have held significant interest in developing this crucial component for wireless communication systems by employing a variety of design techniques. In the past few years, demands for electrically small antennas continues to increase, particularly among portable and mobile wireless devices, medical electronics and aerospace systems. This trend toward smaller electronic devices makes the three dimensional (3D) antennas very appealing, since they can be designed in a way to use every available space inside the devise. Additive Manufacturing (AM) method could help to find great solutions for the antennas design for next generation of wireless communication systems. In this thesis, the design and fabrication of 3D printed antennas using AM technology is studied. To demonstrate this application of AM, different types of antennas structures have been designed and fabricated using various manufacturing processes. This thesis studies, for the first time, embedded conductive 3D printed antennas using PolyLactic Acid (PLA) and Acrylonitrile Butadiene Styrene (ABS) for substrate parts and high temperature carbon paste for conductive parts which can be a good candidate to overcome the limitations of direct printing on 3D surfaces that is the most popular method to fabricate conductive parts of the antennas. This thesis also studies, for the first time, the fabrication of antennas with 3D printed conductive parts which can contribute to the new generation of 3D printed antennas

Long-term effects of thermal variation on the performance of Balanced Twisted Pair Cabling

Remote powering over the Ethernet (including PoE, PoE+ and PoE++) is currently trending as a cost-effective option to power networked devices using balanced twisted pair cabling. As technology advances and Ethernet penetration grows, more devices are deployed, thereby increasing the cabling density to support these devices. Power delivery through Ethernet cables has numerous benefits, including cost and space saving. However, concurrent high-power transmission and installation conditions could induce local heating, and thus, thermal variation may occur in the cable bundles, and these can be exacerbated by the installation conditions, and sometimes by extreme weather conditions. Over a long time, all these could modify the cable properties, thus affecting the performance of the cabling system and thereby impacting the Ethernet signal integrity. Although Joule heating of the cable bundle is primarily assumed to be concomitants of current transmission through the cable, several fundamental questions around these processes are not yet fully answered. They include: Do cable heating and thermal variations influence the designed transmission parameters of the cable? If yes, how can the cause(s) and effects be accurately measured and reliably validated? In answering some of these questions, a series of experiments were developed and adopted to (1) assess cable bundle heating (2) assess the performance of Balanced Twisted Pair cables subject to repeated thermal variation, both within the specified operating range and beyond to account for the situations where high temperature and localised heating might stress the cables beyond the designed or expected levels (3) assess the performance of Ethernet cable dielectrics to understand some of the root causes of Ethernet cable performance degradation. The outcome of the research showed that high power (100 watts) deployment over bundled and insulated unshielded Ethernet cables triggered an extremely high-temperature increase (~ 1400C) that resulted in mechanical failure of the cables’ dielectrics and a short circuit between the copper conductors of the cables. Larger cable conductor size, screening of the twisted pair along with Fluoropolymers as the conductor insulation helped the shielded cables not to reach a point of failure when tested in the insulated environments and at high power levels even though there was a temperature rise on the cables. Moreover, repeated resistive and non- resistive heating have adverse effects on the electrical properties and transmission parameters of Balanced Twisted Pair cables, most notably in the first few cycles. The impact was more pronounced during the cooling phase than the heating phase. Also, the thermal impact was more accentuated in insulated operating condition than in ventilated operating condition. The electrical length of the cable measured by the tester decreased by 0.7 m 5 due to the effect of repeated non-resistive heating in an insulated environment and at a high temperature of ~1200C but decreased by 0.4 m with ~700C in a similar insulated environment. Phase drifts in Balanced Twisted Pair cables were observed to be dependent on the combined effects of mechanical dimension, dielectric constant and frequency. Thermal variation caused a phase change in the Return Loss (RL) signal from 630 to 900, from 900 to 1350 and from 1350 to 3150 respectively. The RL performance of Category 6 U/UTP CoMmunications Plenum rated (CMP) cable failed at 200C and recovered at 230C initially, but after the electrical length of the cable had decreased, subsequent failure and recovery temperatures accelerated towards higher temperature (400C). Similarly, the transition temperatures of the bandwidth of the cavity loaded with the Fluorinated Ethylene Propylene (FEP) from the Category 6 U/UTP CMP cable accelerated during the prolonged thermal cycling. The maximum reduction in the RL value of Category 6A F/UTP cable due to the 40 thermal cycles conducted was observed to be 5 % per degree, whereas the maximum Insertion Loss (IL) increase was 5.8 % per degree. Moreover, for the 24 thermal cycles conducted on Category 6 U/UTP CMP cable, an increase in IL of ~8.3 % per degree was observed while RL decreased by ~6.8 % per degree. Using the Features Selective Validation technique, the comparison between the baseline performance and long-term performance of Category 6A F/UTP permanent link (PL) showed a fair agreement, which implies degradation in the performance of the cable. Furthermore, results showed that impedance varied significantly along the length of the cable due to localised heating of the cable. The impedance along the unheated sides of the cable reverted at every 2 (0.4 m) and 4 (0.2 m) but the impedance profile of the heated middle portion of the cable varied significantly. The results of the Scanning Electron Microscope revealed the deformation in the conductor insulation of a twisted pair sample. Furthermore, the adhesion of the twisted pair conductor insulation to its copper conductor was also observed to be affected near the end of the twisted pair sample. Connector impedance mismatch was observed to be severe on the split pair pins (pair 3,6) than other pairs in the cable. The connector impedance mismatch also dominated the Near End Crosstalk (NEXT) loss at frequencies around 35 MHz. The repeated heating of the cable to a higher temperature of 1200C caused the loss of the PL at room temperature and a DC contact resistance issue which of course resulted in poor intra-pair resistance unbalance between the split pair. The Transverse Conversion Loss (TCL) and Equal Level Transverse Conversion Transfer Loss (ELTCTL) of Category 6 U/UTP CMP PL revealed some imbalances in the structure of the twisted pairs. Also, the equivalent differential mode noise voltages for the TCL values of the cable revealed a voltage spike following the decrease in the electrical length of the cable. More also, Crosstalk performance between the longest and shortest pair in the Category 6A 6 F/UTP cable was also observed to be better due to the heating of the cable in comparison to the crosstalk loss measured due to the cooling of the cable. Crosstalk performance of the portion insulated cables was initially worse during the first few heating and cooling cycles but improved afterwards. In addition, crosstalk, which was not initially present at the reference plane of the permanent link, was observed to increase rapidly from the point where the electrical length decreased. The increase in temperature to ~650C caused an accentuated frequency shift in the resonance of the FEP, which is the probable cause of the immediate performance degradation of the Category 6 U/UTP CMP cable. The dielectric constant of the extracted FEP rod sample from Category 6 U/UTP CMP cable increased as a consequence of prolonged thermal cycling, particularly during the cooling phase, which also suggests the root cause of the poor RL performance observed during the cooling phase. The increased loss tangent of the FEP during thermal cycling also indicates that IL performance degradation of the Ethernet cables will increase during the heating and cooling process in Ethernet cables. Also, on a long-term, IL performance will drift due to thermal cycling. Furthermore, various signal phase transitions were recorded during the heating and cooling of the cable and its dielectric due to the different behaviour of the molecular transitions. As a result, an echo of RL was measured during the transition between the intermittent and prolonged thermal cycling of the cable, of which can be correlated to the spurious resonance, observed in the resonance of the FEP sample during the transition period. Thus, it could be inferred that immediate and longterm effects of thermal variation influence the designed electrical properties and transmission parameters of Balanced Twisted Pair cables. Also, an immediate and long-term effect of thermal variation on the conductor insulation of the cable has a direct effect on the performance of Balanced Twisted Pair Cables

Design, fabrication and testing of a novel W-band monolithic millimetre-wave integrated circuit mixer

Abstract available: p. [1

The Random Line-of-Sight Over-the-Air Measurement System

As our society becomes increasingly connected, a growing number of devices rely on wireless connectivity. The type, use and form factor of these devices range from wearables to entire vehicles. Additionally, the fifth generation of wireless communication (5G) introduces new communication bands, also at higher frequencies. At these millimeter-wave frequencies, large portions of bandwidth are available which are needed in order to increase the data rates.In this scenario, testing and verifying the wireless communication performance has an increasingly important role. In modern devices, testing needs to be performed over-the-air (OTA), as direct conducted measurements to the antenna ports become unfeasible. Moreover, there is still ongoing research to understand how testing should be performed for devices with large form-factors, such as vehicles, as well as for higher frequencies. The proposed methods are mainly based on techniques for mobile phone testing at the current communication bands, i.e., sub-6 GHz. However, scaling and adapting these methods to work for future needs presents challenges. A possible solution to meet the future testing requirements is offered by the following hypothesis: "If a wireless device is tested with good performance in both pure-LOS and RIMP environments, it will also perform well in real-life environments and situations, in a statistical sense". The rich isotropic multipath (RIMP) and the random line-of-sight (random-LOS) are therefore identified as the two representative edge environments for testing. This thesis focuses on the random-LOS environment, and its practical realization to test the wireless performance of different devices. The thesis is divided into three main parts. The first part describes the practical realization of random-LOS OTA measurement setups. Three different setups are presented, a virtual planar array and two reflector antennas. One reflector system is aimed at vehicular testing for frequencies below 6 GHz, while the other targets smaller devices at 28 GHz. The second part of the thesis focuses on numerical and experimental verification of the random-LOS measurement setups. In the verification, numerical simulations and measurements of the test zone variations are compared for the proposed OTA measurement systems.The third and last part focuses on how passive and active measurements can be performed using a random-LOS measurement setup. The measurements demonstrate the application of the designed OTA measurement systems for passive antenna measurements, as well as active 2x2 multiple-input multiple-output (MIMO) measurements on a complete vehicle

Development and performance evaluation of a multistatic radar system

Multistatic radar systems are of emerging interest as they can exploit spatial diversity, enabling improved performance and new applications. Their development is being fuelled by advances in enabling technologies in such fields as communications and Digital Signal Processing (DSP). Such systems differ from typical modern active radar systems through consisting of multiple spatially diverse transmitter and receiver sites. Due to this spatial diversity, these systems present challenges in managing their operation as well as in usefully combining the multiple sources of information to give an output to the radar operator. In this work, a novel digital Commercial Off-The-Shelf (COTS) based coherent multistatic radar system designed at University College London, named ‘NetRad’, has been developed to produce some of the first published experimental results, investigating the challenges of operating such a system, and determining what level of performance might be achievable. Full detail of the various stages involved in the combination of data from the component transmitter-receiver pairs within a multistatic system is investigated, and many of the practical issues inherent are discussed. Simulation and subsequent experimental verification of several centralised and decentralised detection algorithms in terms of localisation (resolution and parameter estimation) of targets was undertaken. The computational cost of the DSP involved in multistatic data fusion is also considered. This gave a clear demonstration of several of the benefits of multistatic radar. Resolution of multiple targets that would have been unresolvable in a conventional monostatic system was shown. Targets were also shown to be plotted as two-dimensional vector position and velocities from use of time delay and Doppler shift information only. A range of targets were used including some such as walking people which were particularly challenging due to the variability of Radar Cross Section (RCS). Performance improvements were found to be dependant on the type of multistatic radar, method of data fusion and target characteristics in question. It is likely that future work will look to further explore the optimisation of multistatic radar for the various measures of performance identified and discussed in this work

Free-Space Measurements of Dielectrics and Three-Dimensional Periodic Metamaterials

This thesis presents the free-space measurements of a periodic metamaterial structure. The metamaterial unit cell consists of two dielectric sheets intersecting at 90 degrees. The dielectric is a polyetherimide-based material 0.001” thick. Each sheet has a copper capacitively-loaded loop (CLL) structure on the front and a cut-wire structure on the back. Foam material is used to support the unit cells. The unit cell repeats 40 times in the x-direction, 58 times in the y-direction and 5 times in the z-direction. The sample measures 12” × 12” × 1” in total. We use a free-space broadband system comprised of a pair of dielectric-lens horn antennas with bandwidth from 5.8 GHz to 110 GHz, which are connected to a HP PNA series network analyzer. The dielectric lenses focus the incident beam to a footprint measuring 1 wavelength by 1 wavelength. The sample holder is positioned at the focal point between the two antennas. In this work, the coefficients of transmission and reflection (the S-parameters S21 and S11) are measured at frequencies from 12.4 GHz up to 30 GHz. Simulations are used to validate the measurements, using the Ansys HFSS commercial software package on the Arkansas High Performance Computing Center cluster. The simulation results successfully validate the S-parameters measurements, in particular the amplitudes. An algorithm based on the Nicolson-Ross-Weir (NRW) method is implemented to extract the permittivity and permeability values of the metamaterial under test. The results show epsilon-negative, mu-negative and double-negative parameters within the measured frequency range

Channel characteristics for intra-vehicle wireless communications

Vehicles are continuously being improved to enhance the driving experience by integrating new technologies. Recent luxury vehicles may have over 70 Electronic Control Units (ECU) and 2200 cables. It is estimated that the number of ECUs and connections between ECUs and sensors will continuously increase to meet growing network requirements. The wire harness is the third most expensive component in a vehicle, reducing the number of cables through wireless communications would consequently result in space, cost, and fuel savings. However, the behaviour of the intra-vehicle channel and suitable wireless network technologies for an intra-vehicle network have not been fully addressed. In this research, the intra-vehicle narrowband loss performance in non-line-of-sight and line-of-sight condition was investigated and compared through real field tests. The results indicate that fading behaviour is primarily caused by small-scale rather than large-scale fading. An empirical-based path loss model is proposed with its parameters extracted from the real field test measurements. Further analysis of the small-scale fading through Rician K-factor reveals the dependence of the K-factor with distance and locations. These investigations suggest that for a narrowband system whereby the bandwidth of the transmitted signal is lower than the coherence bandwidth; the channel can be modelled using Rician fading. Furthermore, the wideband and ultra-wideband channel was characteristics through a real field tests. The results demonstrate that the multipath fading of intra-vehicle channel is much worse than other type of environments such as factory workshops and hospitals. Finally, the time-varying characteristics of the intra-vehicle channel, tested under various scenarios, suggest that the channel's coherence time is primarily impacted by passenger motion in the vehicle. Considering both the channel loss and time-varying characteristics, the performance trade-off's of the cooperative communication system against retransmission was evaluated

Design of Circuits to enhances the performace of high frequency planar Gunn diodes

The project contains adventurous research, with an aim to understand and design a planar Gunn diode with a novel integrated circuit configuration to extract the 2nd harmonic. This will potentially enhance the Gunn diode as a high frequency source towards frequencies in excess of 600 GHz. The RF performance from the above integrated circuit was achieved by design and simulation of radial and diamond stub resonators, which were used to short the fundamental oscillation frequency while allowing the second harmonic frequency to pass through to the load. The diamond stub resonator is a new configuration offering a number of advantages which include a higher loaded quality factor and occupies 55% less chip area than a comparable radial stub resonator. The designed novel circuits with integrated planar Gunn diode were fabricated using microwave monolithic integrated circuits (MMIC) technology at the James Watt Nanofabrication centre in Glasgow University. Full DC and microwave characterisation of the diodes and integrated circuits with diodes was carried out using a semiconductor analyser, network analyser (10 MHz to 110GHz) and spectrum analyser (10 MHz to 125GHz). The microwave measurements were carried out at the high frequency RF laboratories in Glasgow University. Both GaAs and InP based Gunn diodes were characterised and RF characterisation work showed that higher fundamental frequencies could be obtained from Gunn diodes fabricated on InGaAs on a lattice matched InP substrate. Planar Gunn diodes with an anode to cathode spacing of 4 microns giving a fundamental frequency of oscillation of 60 GHz were fabricated as an integrated circuit with coplanar waveguide (CPW) circuit elements to extract the second harmonic. A second harmonic frequency of 120 GHz with an RF output power of -14.11 dBm was extracted with very good fundamental frequency suppression. To the authors knowledge this was the first time second harmonic frequencies have been extracted from a planar Gunn diode technology. Aluminium gallium arsenide (AlGaAs) planar Gunn diodes were also designed with an integrated series inductor to match the diode at the fundamental frequency to obtain higher RF output powers. Devices with a 1 micron anode to cathode separation gave the highest fundamental oscillation frequency of 121 GHz the highest reported for a GaAs based Gunn diode and with an RF output power of -9 dBm. These circuits will have potential applications in secure communications, terahertz imaging etc. The research programme was in collaboration with the University of Glasgowwould like to thank the staff of the James Watt Nanofabrication Centre at the University of Glasgow for help in fabricating the devices which is reported in this thesis. ‘Part of this work was supported by ESPRC through EP/H011862/1, and EP/H012966/1

Architectures and Algorithms for the Signal Processing of Advanced MIMO Radar Systems

This thesis focuses on the research, development and implementation of novel concepts, architectures, demonstrator systems and algorithms for the signal processing of advanced Multiple Input Multiple Output (MIMO) radar systems. The key concept is to address compact system, which have high resolutions and are able to perform a fast radar signal processing, three-dimensional (3D), and four-dimensional (4D) beamforming for radar image generation and target estimation. The idea is to obtain a complete sensing of range, Azimuth and elevation (additionally Doppler as the fourth dimension) from the targets in the radar captures. The radar technology investigated, aims at addressing sev- eral civil and military applications, such as surveillance and detection of targets, both air and ground based, and situational awareness, both in cars and in flying platforms, from helicopters, to Unmanned Aerial Vehicles (UAV) and air-taxis. Several major topics have been targeted. The development of complete systems and innovative FPGA, ARM and software based digital architectures for 3D imaging MIMO radars, which operate in both Time Division Multiplexing (TDM) and Frequency Divi- sion Multiplexing (FDM) modes, with Frequency Modulated Continuous Wave (FMCW) and Orthogonal Frequency Division Multiplexing (OFDM) signals, respectively. The de- velopment of real-time radar signal processing, beamforming and Direction-Of-Arrival (DOA) algorithms for target detection, with particular focus on FFT based, hardware implementable techniques. The study and implementation of advanced system concepts, parametrisation and simulation of next generation real-time digital radars (e.g. OFDM based). The design and development of novel constant envelope orthogonal waveforms for real-time 3D OFDM MIMO radar systems. The MIMO architectures presented in this thesis are a collection of system concepts, de- sign and simulations, as well as complete radar demonstrators systems, with indoor and outdoor measurements. Several of the results shown, come in the form of radar images which have been captured in field-test, in different scenarios, which aid in showing the proper functionality of the systems. The research activities for this thesis, have been carried out on the premises of Air- bus, based in Munich (Germany), as part of a Ph.D. candidate joint program between Airbus and the Polytechnic Department of Engineering and Architecture (Dipartimento Politecnico di Ingegneria e Architettura), of the University of Udine, based in Udine (Italy).Questa tesi si concentra sulla ricerca, lo sviluppo e l\u2019implementazione di nuovi concetti, architetture, sistemi dimostrativi e algoritmi per l\u2019elaborazione dei segnali in sistemi radar avanzati, basati su tecnologia Multiple Input Multiple Output (MIMO). Il con- cetto chiave `e quello di ottenere sistemi compatti, dalle elevate risoluzioni e in grado di eseguire un\u2019elaborazione del segnale radar veloce, un beam-forming tri-dimensionale (3D) e quadri-dimensionale (4D) per la generazione di immagini radar e la stima delle informazioni dei bersagli, detti target. L\u2019idea `e di ottenere una stima completa, che includa la distanza, l\u2019Azimuth e l\u2019elevazione (addizionalmente Doppler come quarta di- mensione) dai target nelle acquisizioni radar. La tecnologia radar indagata ha lo scopo di affrontare diverse applicazioni civili e militari, come la sorveglianza e la rilevazione di targets, sia a livello aereo che a terra, e la consapevolezza situazionale, sia nelle auto che nelle piattaforme di volo, dagli elicotteri, ai Unmanned Aerial Vehicels (UAV) e taxi volanti (air-taxis). Le tematiche affrontante sono molte. Lo sviluppo di sistemi completi e di architetture digitali innovative, basate su tecnologia FPGA, ARM e software, per radar 3D MIMO, che operano in modalit`a Multiplexing Time Division Multiplexing (TDM) e Multiplexing Frequency Diversion (FDM), con segnali di tipo FMCW (Frequency Modulated Contin- uous Wave) e Orthogonal Frequency Division Multiplexing (OFDM), rispettivamente. Lo sviluppo di tecniche di elaborazione del segnale radar in tempo reale, algoritmi di beam-forming e di stima della direzione di arrivo, Direction-Of-Arrival (DOA), dei seg- nali radar, per il rilevamento dei target, con particolare attenzione a processi basati su trasformate di Fourier (FFT). Lo studio e l\u2019implementazione di concetti di sistema avan- zati, parametrizzazione e simulazione di radar digitali di prossima generazione, capaci di operare in tempo reale (ad esempio basati su architetture OFDM). Progettazione e sviluppo di nuove forme d\u2019onda ortogonali ad inviluppo costante per sistemi radar 3D di tipo OFDM MIMO, operanti in tempo reale. Le attivit`a di ricerca di questa tesi sono state svolte presso la compagnia Airbus, con sede a Monaco di Baviera (Germania), nell\u2019ambito di un programma di dottorato, svoltosi in maniera congiunta tra Airbus ed il Dipartimento Politecnico di Ingegneria e Architettura dell\u2019Universit`a di Udine, con sede a Udine