Tunable antennas have emerged as a promising technology to address the challenges of achieving optimal performance across a wide range of frequencies. This abstract presents a study focused on designing and implementing an ideal antenna system design within a closed-loop system. Background. Tunable antennas offer a solution for achieving efficient signal transmission and reception over a broad spectrum. Traditionally fixed-frequency antennas have limitations in terms of bandwidth and efficiency, making them unfit for applications requiring adaptability to varying frequencies. The integration of tunable components in antenna systems results in greater flexibility and improved performance. Objectives. The main objective of this research is to evaluate and determine the ideal antenna design for closed-loop antenna systems which achieves maximum frequency coverage and efficiency. This involves the design of an architecture that seamlessly integrates components. Methods. The experimental methodology involves designing an antenna system design. The selected components are interconnected in a closed loop, allowing continuous monitoring and adjustment of the antenna’s characteristics. The Micro Controlling Unit (MCU) is programmed using the Arduino Integrated Development Environment (IDE), serves as the controller for managing the antenna tuner’s settings based on real-time feedback from the directional coupler and power detector. The bi-directional logic level converter ensures proper voltage compatibility between the MCU and the antenna tuner. Results. The results of the study showed that the proposed antenna system architecture was able to achieve the desired goals. The implemented closed-loop system demonstrates significant enhancements in frequency coverage and efficiency of the selected antenna. The antenna system was also able to maintain its efficiency even when the environment changed. Conclusions. The experimental results show that in closed-loop systems the performance of an antenna is optimised. The integration of the components enables dynamic frequency tuning, by enhancing the antenna’s maximum frequency coverage and efficiency. The results underscore the potential of tunable antennas in revolutionizing wireless communication systems, showing the way for more adaptable and high-performance devices in various applications.

The increasing energy demand, combined with the use of harmful non-renewable energy sources calls for the search of alternative methods to cover our energy need.Renewable energy can be harvested in different ways, through the movement of wind and water, biomass, or directly from the rays of the sun, as in the case of photovoltaic (PV) devices. Whilst crystalline silicon (c-Si) is the most common absorber used for solar cells, other technologies are emerging. Solar cells with copper indium gallium diselenide (CIGS) as an absorber have the possibility of being flexible, which is an advantage due to the many more application possibilities that appear compared to the rigid and heavy c-Si solar cells. CIGS solar cells have some long-term stability issues, especially regarding ingression of atmospheric species through the front contact layer. This calls for further research in the front contact of the CIGS solar cell, exploring alternative materials to prevent degradation. The front contact of a solar cell must be both optically transparent and conduct electricity. Transparent conductive oxides (TCO) are materials characterized by the ability to conduct electricity, while also possessing a certain degree of optical transparency. The combination of conductivity and transparency makes TCOs ideal as front contacts in solar cells. A very common TCO for front contacts in CIGS solar cells is aluminum-doped zinc oxide (AZO) due to its low cost, good electrical conductivity and optical transparency. Because of its low resistance to degradation in humid environments more robust TCO alternatives, such as indium-doped tin oxide (ITO), are being investigated. Indium-doped tin oxide possesses similar electrical and optical properties as AZO, but better stability in humid environments.The ITO was deposited through RF magnetron sputtering, on a glass substrate to be able to measure optical properties. Initially, experiments focusing on oxygen content in the deposition atmosphere were done, together with a reproducibility experiment. This gave useful information about sputtering parameters and stability of the deposition. Thereon, an experiment was done varying three parameters: oxygen content in deposition atmosphere, sputtering power and temperature of substrate. A statistical software was used to analyze the data, identifying the effects of the changing parameters. The best performing samples were made with an oxygen content of 0,4-0,6 vol%. A high sensibility for oxygen in the system was also observed, as a result of the initial reproducibility experiments. This led to the introduction of a sacrificial deposition step after the machine had been shut down. Optimal substrate temperature was around 150°Cand it was not possible to go higher due to sensibility of the underlying solar cell layers.A lower threshold for the film thickness, located somewhere between 125 and 175 nm, was observed. Films with thickness below this threshold experienced a large resistivityincrease. Further depositions with higher oxygen content are advised to see if the properties of the films further improve.

The objective of this research work is to investigate, design and measurement of a digital predistortion linearizer that is able to compensate the dynamic nonlinear distortion of a High Power Amplifier (PA). The effectiveness of the proposed baseband predistorter (PD) on the performance of a WLAN OFDM transmitter utilizing a nonlinear PA with memory effect is observed and discussed. For this purpose, a 10W Class-A/B power amplifier with a gain of 22 dB, operated over the 3.5 GHz frequency band was designed and implemented. The proposed baseband PD is independent of the operating RF frequency and can be used in multiband applications. Its operation is based on the Hammerstein system, taking into account PA memory effect compensation, and demonstrates a noticeable improvement compared to memoryless predistorters. Different types of modelling procedures and linearizers were introduced and investigated, in which accurate behavioural models of Radio Frequency (RF) PAs exhibiting linear and nonlinear memory effects were presented and considered, based on the Wiener approach employing a linear parametric estimation technique. Three new linear methods of parameter estimation were investigated, with the aim of reducing the complexity of the required filtering process in linear memory compensation. Moreover, an improved wiener model is represented to include the nonlinear memory effect in the system. The validity of the PA modelling approaches and predistortion techniques for compensation of nonlinearities of a PA were verified by several tests and measurements. The approaches presented, based on the Wiener system, have the capacity to deal with the existing trade-off between accuracy and convergence speed compared to more computationally complex behavioural modelling algorithms considering memory effects, such as those based on Volterra series and Neural Networks. In addition, nonlinear and linear crosstalks introduced by the power amplifier nonlinear behaviour and antennas mutual coupling due to the compact size of a MIMO OFDM transmitter have been investigated.

The aim of this study is to analysis, investigate and find out the solutions for the problems associated with the implementations of antennas RFID Reader and Tag for various applications. In particular, the efficiency of the RFID reader antenna and the detection range of the RFID tag antenna, subject to a small and compact antenna¿s design configuration have been studied. The present work has been addressed directly to reduce the cost, size and increase the detection range and communication reliability of the RFID framework antennas. Furthermore, the modelling concept of RFID passive tags mounted on various materials including the novel design of RFID reader antenna using Genetic Algorithm (GA) are considered and discussed to maintain reliable and efficient antenna radiation performances. The main benefit of applying GA is to provide fast, accurate and reliable solutions of antenna¿s structure. Therefore, the GA has been successfully employed to design examples: meander-line, two linear cross elements and compact Helical- Spiral antennas. In addition, a hybrid method to model the human body interaction with RFID tag antenna operating at 900MHz has been studied. The near field distribution and the radiation pattern together with the statistical distribution of the radiation efficiency and the absorbed power in terms of cumulative distribution functions for different orientation and location of RFID¿s tag antenna on the human body have been demonstrated. Several tag antennas wi th symmetrical and unsymmetrical structure configurations operating in the European UHF band 850-950 MHz have been fabricated and tested. . The measured and simulated results have been found to be in a good agreement with reasonable impedance matching to the typical input impedance of an RFID integrated circuit chip and nominal power gain and radiation patterns.

Sewer and oil pipeline spillage issues have become major causes of pollution in urban and rural areas usually caused by blockages in the water storage and drainage system, and oil spillage of underground oil pipelines. An effective way of avoiding this problem will be by deploying some mechanism to monitor these installations at each point in time and reporting unusual liquid activity to the relevant authorities for prompt action to avoid a flooding or spillage occurrence. This research work presents a low cost energy efficient liquid level monitoring technique using Radio Frequency Identification Technology. Passive UHF RFID tags have been designed, modelled and optimized. A simple rectangular tag, the P-shaped tag and S-shaped tag with UHF band frequency of operation (850-950 MHz) has been designed and modelled. Detailed parametric analysis of the rectangular tag is made and the optimised design results analysed and presented in HFSS and Matlab. The optimised rectangular tag designs are then deployed as level sensors in a gully pot. Identical tags were deployed to detect 4 distinct levels in alternate positions and a few inches in seperation distance within the gully pot height (Low, Mid, High and Ultra high). The radiation characteristic of tag sensors in deployment as modelled on HFSS is observed to show consistent performance with application requirements. An in-manhole chamber antenna for an underground communication system is analysed, designed, deployed and measured. The antenna covers dual-band impedance bandwidths (i.e. 824 to 960 MHz, and 1710 to 2170 MHz). The results show that the antenna prototype exhibits sufficient impedance bandwidth, suitable radiation characteristics, and adequate gains for the required underground wireless sensor applications. Finally, a Linearly Shifted Quadrifilar Helical Antenna (LSQHA) designed using Genetic Algorithm optimisation technique for adoption as an RFID reader antenna is proposed and investigated. The new antenna confirms coverage of the RFID bandwidth 860-960 MHz with acceptable power gain of 13.1 dBi. / Petroleum Technology Development Fund (PTDF) and National Space Research and Development Agency (NASRDA).

This research work has made an effort to understand a novel line of radio frequency power amplifiers (RFPAs) that address initiatives for efficiency enhancement and linearity compensation to harmonize the fifth generation (5G) campaign. The objective is to enhance the performance of an orthogonal frequency division multiplexing-long term evolution (OFDM-LTE) transmitter by reducing the nonlinear distortion of the RFPA. The first part of this work explores the design and implementation of 15.5 W class AB RF power amplifier, adopting a balanced technique to stimulate efficiency enhancement and redeeming exhibition of excessive power in the transmitter. Consequently, this work goes beyond improving efficiency over a linear RF power amplifier design; in which a comprehensive investigation on the fundamental and harmonic components of class F RF power amplifier using a load-pull approach to realise an optimum load impedance and the matching network is presented. The frequency bandwidth for both amplifiers was allocated to operate in the 2.620-2.690 GHz of mobile LTE applications. The second part explores the development of the behavioural model for the class AB power amplifier. A particular novel, Hammerstein-Wiener based model is proposed to describe the dynamic nonlinear behaviour of the power amplifier. The RF power amplifier nonlinear distortion is approximated using a new linear parameter approximation approach. The first and second-order Hammerstein-Wiener using the Normalised Least Mean Square Error (NLMSE) algorithm is used with the aim of easing the complexity of filtering process during linear memory cancellation. Moreover, an enhanced adaptive Wiener model is proposed to explore the nonlinear memory effect in the system. The proposed approach is able to balance between convergence speed and high-level accuracy when compared with behavioural modelling algorithms that are more complex in computation. Finally, the adaptive predistorter technique is implemented and verified in the OFDM transceiver test-bed. The results were compared against the computed one from MATLAB simulation for OFDM and 5G modulation transmitters. The results have confirmed the reliability of the model and the effectiveness of the proposed predistorter. / Fundacão para a Ciência e a Tecnologia, Portugal, under European Union’s Horizon 2020 research and innovation programme ... grant agreement H2020-MSCA-ITN- 2016 SECRET-722424 I also acknowledge the role of the National Space Research and Development Agency (NASRDA) Sokoto State Government Petroleum Technology Trust Fund (PTDF)

The demand for high-performance Radio Frequency (RF) passive devices has been steadily increasing due to the growing complexity and sophistication of wireless communication systems. The Quality factor (Q-factor) is a key parameter for describing the signal losses and the energy efficiency of resonators. Previous studies have been done on the spin coating technique of intermediate coating, which presented some limitations in terms of 3D resonators. In this master thesis, we investigate the development of a intermediate layer using dip coating to enhance the Q-factor, i.e., the performance of RF passive devices. The dip coating method is applied to add a nano ceramic coating to the 3D structure as the intermediate layer between the resonator ceramic substrate and the conductive silver coating. After the fabrication process, the samples are observed under Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) and tested with Vector Network Analysis (VNA). Analysis and calculations are mainly conducted with the software Matlab and Gwyddion. The proposed technique improves the smoothness of the samples by 78.95%, and the Q-factor is tested to have a 20.87% enhancement using VNA. The results demonstrate that the intermediate layer with the dip coating technique significantly improves the performance of RF passive devices by reducing the roughness of the resonator surface. These findings open up new opportunities for the design and development of high-performance RF passive devices in various applications, including wireless communication systems, radar systems, and satellite communication. Further studies can be carried out to reduce defects during fabrication and to stabilize the performance of the silver coating. / Efterfrågan på högpresterande passiva RF-enheter har stadigt ökat på grund av den växande komplexiteten och sofistikeringen hos trådlösa kommunikationssystem. Q-faktorn är en viktig parameter för att beskriva signalförluster och energieffektivitet hos resonatorer. Tidigare studier har gjorts på spin coating-tekniken för intermediära beläggningar, vilket presenterade vissa begränsningar för 3D-resonatorer. I denna masteruppsats undersöker vi utvecklingen av ett intermediärt lager med hjälp av doppbeläggning för att förbättra Q-faktorn, det vill säga prestandan hos passiva RF-enheter. Doppbeläggningstekniken tillämpas för att lägga till en nanokeramisk beläggning på 3D-strukturen som intermediärt lager mellan resonatorns keramiska substrat och den ledande silverbeläggningen. Efter tillverkningsprocessen observeras proverna med SEM och AFM och testas med VNA. Analys och beräkningar utförs främst med programvaran Matlab och Gwyddion. Den föreslagna tekniken förbättrar provernas släthet med 78.95%, och Q-faktorn testas och visar en förbättring med 20.87% med hjälp av VNA. Resultaten visar att det intermediära lagret med doppbeläggningstekniken signifikant förbättrar prestandan hos passiva RF-enheter genom att minska ojämnheten på resonatorns yta. Dessa resultat öppnar upp nya möjligheter för design och utveckling av högpresterande passiva RF-enheter inom olika tillämpningsområden, inklusive trådlösa kommunikationssystem, radarssystem och satellitkommunikation. Ytterligare studier kan genomföras för att minska defekter under tillverkningen och stabilisera prestandan hos silverbeläggningen.

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