<p dir="ltr">Accurately locating a radio-frequency (RF) emitter is imperative in the defense sector, and passive direction finding systems are intriguing due to relatively low cost. This approach involves using the time difference between a signal’s impact at equispaced antennas to determine the location of the emitter, a particular challenge for wideband waveforms operating near the noise floor. Microwave photonic systems have been demonstrated for passive direction finding. These techniques possessed drawbacks, such as reliance on the incoming signal’s bandwidth, dependence on laser power, or the inability to recover an angle from wideband pulses. This thesis presents a novel approach to passive direction finding by translating the methods of spectral interferometry from the optical domain to RF. Spectral interferometry involves interfering a time-delayed reference pulse with a “signal” pulse that has passed through an unknown system. By removing the spectral phase of the reference pulse from the resulting interferogram, the spectral phase of the uncharacterized system is recovered. This enables direction-finding for many waveforms, including the wideband low peak power chirps frequently used in radar. Incorporating an analog optical delay line into both a hard-wired RF interferometer and a two-element antenna array demonstrated spectral interferometric processing of chirped signals with up to 1 GHz instantaneous bandwidth. The technique extracted accurate delays and angles to within 2$\degree$ throughout testing. This approach only requires the imposed delay be longer than the autocorrelation of the bandwidth limited pulses. With additional backend processing, this method could simultaneously determine the angle and classify the incoming signal.</p>

Yes / This is the ninth workshop to be organised under the postgraduate programmes in electrical and electronic engineering (EEE). The workshop concludes the Research Seminar Series, which has provided a platform for disseminating the latest research activities in related technologies through its weekly seminars. The EEE courses cover a broad range of technologies and this is reflected in the variety of topics presented during the workshop. In total, forty-four papers have been selected for the proceedings, which have been divided into eight sections. The workshop aims to be as close to a `real¿ event as possible. Hence, authors have responded to a Call for Papers with an abstract, prior to the submission of the final paper. This has been a novel experience for many, if not all of the contributors. As usual, authors have taken up the challenge with enthusiasm, resulting in a collection of papers that reflects today¿s research challenges. / School of Engineering, Design and Technology

Yes / This is the eighth workshop to be organised under the postgraduate programmes in electrical and electronic engineering (EEE). The workshop concludes the Research Seminar Series, which has provided a platform for disseminating the latest research activities in related technologies through its weekly seminars. The EEE courses cover a broad range of technologies and this is reflected in the variety of topics presented during the workshop. In total, thirty-three papers have been selected for the proceedings, which have been divided into seven sections. The workshop aims to be as close to a `real¿ event as possible. Hence, authors have responded to a Call for Papers with an abstract, prior to the submission of the final paper. This has been a novel experience for many, if not all of the contributors. Clearly, authors have taken up the challenge with enthusiasm, resulting in what promises to be an interesting and informative workshop.

Radio frequency interference (RFI) poses significant challenges for passive microwave radiometry used in climate studies and Earth science. Despite operating in protected frequency bands, microwave radiometers often encounter RFI from sources like air surveillance radars, 5G communications, and unmanned aerial vehicles. Traditional RFI detection methods rely on handcrafted algorithms designed for specific RFI types. This study proposes a deep learning (DL) approach, leveraging convolutional neural networks to detect various RFI types on a global scale. By learning directly from radiometer data, this data-driven method enhances detection accuracy and generalization. The DL framework processes raw moment data and Stokes parameters, dynamically labeled using quality flags, offering a robust and efficient solution for RFI detection. This approach demonstrates the potential for improved RFI mitigation in passive remote sensing applications.

Thesis (M. Tech.) - Central University of Technology, Free State, 2010 / The main aim of this research was to automate student attendance registration, thereby reducing human involvement in the whole process. This was made possible using Radio Frequency Identification (RFID) technology. The Central University of Technology uses student cards that are compatible for use with RFID technology. As a result, no initial investment (except for the existing personal computer’s and the constructed RFID reader) in infrastructure was required for this project. The basic working of the project was as follows. The students belonging to a specific class had their vital educational data (Student number, Name) entered into a database table at the time of registration. A student card containing a serial number, with reference to the data contained in the database table, was given to the students after registration. The students walk into their respective classes and scan their student cards with the RFID reader. The serial number stored in the student card is transferred to the reader and from there wirelessly to the main server using ZigBee technology. In the main server, using Java programming language, the card serial number is sent to the Integrated Development Environment (IDE). In this project the Netbeans IDE (Java platform) was used. The Netbeans IDE is connected to the Apache Derby database using Java Database Connector (JDBC), so the serial number (which is referenced to the educational data of the students) from the student card is automatically compared with the original database created at the time of registration. Once a match is confirmed between the two entries, the data is entered into a separate database table which serves as the basic attendance sheet for a specific day.

Over the course of history, different means of object and person identification as well as verification have evolved for user authentication. In recent years, a new concern has emerged regarding the accuracy of verifiable authentication and protection of personal identifying information (PII), because previous misuses have resulted in significant financial loss. Such losses have escalated more noticeably because of human identity-theft incidents due to breaches of PII within multiple public-access environments. Although the use of various biometric and radio frequency identification (RFID) technologies is expanding, resistance to using these technologies for user authentication remains an issue. This study addressed the effect of individuals’ perceptions on their resistance to using multi-method authentication systems (RMS) in public-access environments and uncovered key constructs that may significantly contribute to such resistance. This study was a predictive study to assess the contributions of individuals’ perceptions of the importance of organizational protection of their PII, noted as Perceived Value of Organizational Protection of PII (PVOP), authentication complexity (AC), and invasion of privacy (IOP) on their resistance to using multi-method authentication systems (RMS) in public-access environments. Moreover, this study also investigated if there were any significant differences on the aforementioned constructs based on age, gender, prior experience with identity theft, and acquaintance experience with identity theft. As part of this study, a rollout project was implemented of multi-factor biometric and RFID technologies for system authentication prior to electronic-commerce (e-commerce) use in public-access environments. The experimental group experienced the multi-factor authentication and also was trained on its use. Computer users (faculty & students) from a small, private university participated in the study to determine their level of PVOP, IOP, and AC on their resistance to using the technology in public-access environments. Multiple Linear Regression (MLR) was used to formulate a model and test predictive power along with the significance of the contribution of the aforementioned constructs on RMS. The results show that all construct measures demonstrated very high reliability. The results also indicate that the experimental group of the multi-factor authentication had lower resistance than the control group that didn’t use the technology. The mean increases indicate an overall statistically significant difference between the experimental and control groups overall. The results also demonstrate that students and participants’ increased levels of education indicate an overall statistically significant decrease in resistance. The findings demonstrate that overall computer authentication training do provide added value in the context of measuring resistance to using newer multi-method authentication technology.

Thesis (PhD)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Square Kilometre Array (SKA) and its demonstrator MeerKAT are being designed to operate over a wide frequency range and are expected to achieve greater sensitivity and resolution than existing telescopes. The radio astronomy community is well aware of the negative impact that radio frequency interference (RFI) has on observations in the proposed frequency band. This is because weak radio signals such as those from pulsars and distant galaxies are difficult to detect on their own. The presence of RFI sources in the telescope’s operating area can severely corrupt observation data, leading to inaccurate or misleading results. Power-line interference and radiation from electric fences are examples of RFI sources. Mitigation techniques for these interference sources in the SKA system’s electromagnetic environment are essential to ensure the success of this project. These techniques can be achieved with appropriate understanding of the characteristics of the noise sources. Overhead power-line interference is known to be caused mainly by corona and gap-type (commonly known as sparking noise) discharges. Sparking noise is the dominant interference for the SKA. It is mainly encountered on wooden pole lines, which are usually distribution lines operated at up to 66 kV AC in the South African network. At this voltage level, the voltage gradients on the lines are insufficient to generate conductor corona. The power requirements for SKA precursors will be below this voltage level. The aim of the research in this dissertation is to evaluate the power line sparking characteristics through measurements and simulation of line radiation and propagation characteristics. An artificially made sparking noise generator, which is mounted on a power line, is used as noise source and the radiation characteristics are measured. Measurements were carried out in different environments, which included a high-voltage laboratory (HV-Lab), a 40m test-line, and another 22-kV test line of approximately 1.5 km. The key sparking noise parameters of interest were the temporal and spectral characteristics. The time domain features considered were the pulse shape and the repetition rate. The lateral, longitudinal and height attenuation profiles were also quantified. Since sparking noise current pulses are injected or induced onto power line conductors, the line will act as an unintentional antenna. The far-field radiation characteristics of the line were evaluated through measurements on physical scale-model structures and simulations. 1/120th and 1/200th scaled lines, using an absorbing material and metallic ground planes, respectively, were simulated in FEKO. The measurements of the constructed scale models were taken in the anechoic chamber. Both measurements and simulations showed that the line exhibits an end-fire antenna pattern mode. Line length, pulse injection point and line configuration were some of the parameters found to affect the radiation patterns. The findings from this study are used to determine techniques to identify the sparking noise, and locate and correct the sources when they occur on the line hardware. Appropriate equipment is recommended to be used for the location and correction of sparking noise. / AFRIKAANSE OPSOMMING: Die Vierkante Kilometer Reeks (SKA) en sy demonstrasie projek, die Karoo Reeks Teleskoop (KAT), word ontwerp om oor 'n wye frekwensie-bereik te funksioneer. Beide sal na verwagting beter sensitiwiteit en resolusie as bestaande radioteleskope he. Die radio-astronomie-gemeenskap is deeglik bewus van die negatiewe impak wat radio-frekwensie steurnisse (RFS) op waarnemings in die voorgestelde frekwensieband het. Die rede hiervoor is dat swak radio-seine soos die van pulsars en verafgelee sterrestelsels inherent moeilik is om te bepaal. Die teenwoordigheid van RFS bronne in die teleskoop se onmiddellike operasionele gebied kan waarnemings nadelig beinvloed. Dit lei uiteindelik tot onakkurate of misleidende resultate. Kraglyne en uitstralings van elektriese heinings is voorbeelde van RFS bronne. Metodes om die oorsake van die steurnisse van die SKA se elektromagnetiese omgewing te verminder is noodsaaklik om die sukses van hierdie projekt te verseker. Dit vereis egter deeglike begrip van die eienskappe van hierdie bronne. Steurnisse as gevolg van oorhoofse kraglyne word hoofsaaklik veroorsaak deur korona en gapingtipe ontladings (algemeen bekend as vonkontladings). Vonkontladings word hier beskou as die belangrikste oorsaak van steurnisse vir die SKA. Dit word in die Suid-Afrikaanse netwerk hoofsaaklik aangetref op houtpaal-installasies, wat gewoonlik bestaan uit distribusie lyne wat tot en met 66 kV wisselstroom (WS) bedryf word. By hierdie operasionele spanning is die spanningsgradient op die lyn onvoldoende om korona op te wek. Die kragvereistes vir die SKA se voorafgaande projekte sal sodanig wees dat hierdie spanningsvlak nie oorskry sal word nie. Die doel van die navorsing omskryf in hierdie proefskrif is om die eienskappe van vonkontladings rondom kraglyne te evalueer. Dit word gedoen met behulp van metings en simulasies van uitstralings- en voortplantingspatrone wat met 'n spesifieke lyn geassosieer kan word. 'n Kunsmatige vonkontladingsopwekker word op 'n kraglyn geplaas en dien as bron om die uitstralingspatrone te meet. Metings is uitgevoer in verskillende omgewings, insluitende 'n hoogspanningslaboratorium (HV-Lab), 'n 40 m toetslyn en 'n 22 kV WS toetslyn van ongeveer 1.5 km lank. Die hoof vonkontladings eienskappe van belang is die temporale en spektrale eienskappe. Die tydgebiedeienskappe wat ondersoek is, is die pulsvorm asook die pulsherhalingskoers. Die laterale, longitudinale en hoogte-attenuasie profiele word ook gekwantifiseer. Aangesien stroompulse deur vonkontladings op die kraglyn geplaas of geinduseer word, sal die lyn as 'n ongewenste antenna optree. Die ver-veld uitstralingskenmerke van die lyn is ook geëvalueer deur gebruik te maak van fisiese skaalmodelstrukture en -simulasies. 1/120ste en 1/200ste geskaleerde lynmodelle, wat onderskeidelik 'n absorberende- en metaalgrondvlak bevat, was gebruik om 'n 3 spanlengte kraglyn te simuleer met behulp van FEKO. Metings van die fisiese skaalmodel strukture is in 'n anegoise kamer geneem. Beide die metings en die simulasies toon dat die lyn 'n endpunt uitstralingspatroon het. Lynlengte, die opwekkingsposisie van die stroompuls en die lynkonfigurasie is 'n paar van die parameters wat die uitstralingpatroon beïnvloed, soos in die navorsing aangedui. Die bevindinge van hierdie studie word gebruik om steurnisse as gevolg van vonkontladings op die kraglyn te identifiseer, op te spoor en uiteindelik reg te stel. Toepaslike toerusting word voorgestel wat gebruik kan word vir die identifisering en opsporing van vonkontladings.

Microelectromechanical systems (MEMS) devices have been increasing in popularity for radio frequency (RF) and microwave communication systems due to the ability of MEMS devices to improve the performance of these circuits and systems. This interdisciplinary field combines the aspects of lithographic fabrication, mechanics, materials science, and RF/microwave circuit technology to produce moving structures with feature dimensions on the micron scale (micro-structures). MEMS technology has been used to improve switches, varactors, and inductors to name a few specific examples. Most MEMS devices have been fabricated using planar micro fabrication techniques that are similar to current integrated circuit (IC) fabrication techniques. These techniques limit the thickness of individual layers to a few microns, and restrict the structures to have planar and not vertical features. One micro fabrication technology that has not seen much application to microwave MEMS devices is LIGA, a German acronym for X-ray lithography, electroforming, and moulding. LIGA uses X-ray lithography to produce very tall structures (hundreds of microns) with excellent structural quality, and with lateral feature sizes smaller than a micron. These unique properties have led to an increased interest in LIGA for the development of high performance microwave devices, particularly as operating frequencies increase and physical device size decreases. Existing work using LIGA for microwave devices has concentrated on statically operating structures such as transmission lines, filters, couplers, and antennas. This research uses these unique fabrication capabilities to develop dynamically operating microwave devices with high frequency performance. This thesis documents the design, fabrication and testing of LIGA-MEMS variable capacitors that exploit the vertical dimension. Also included are methods to improve both the reliable fabrication and operation of these devices as well as material property characterization. Variable capacitors can be found in systems such as voltage-controlled oscillators, filters, impedance matching networks and phase shifters. Important figures-of-merit for these devices include the quality factor (Q), tuning range and tuning voltage. Two different types of variable capacitors are presented, a pull-away design and a design based on the principle of leveraged bending. The pull-away style variable capacitors were found to have high Q-factors, especially the devices fabricated using a thick gold device layer. As an example, the small gold half capacitance electrode design features a Q-factor of 95 at an operating frequency of 5.6 GHz and a tuning ratio of 1.36:1 with a tuning voltage range of 0 to 7.8 V. The design based on leveraged bending significantly improves the tuning ratio to a value of 1.9:1 while still maintaining a high Q-factor similar to those found in the pull-away style designs. A further increase in tuning ratio to a value of approximately 2.7:1 would be possible, based on simulated results, by simply changing the angle of the capacitance electrode in the layout. To improve device performance and fabrication reliability, modifications were made to both the fabrication process and the device layout. In the fabrication process the exposure step, electroplating step, and the etching process were modified to improve the quality of the resulting devices. In the layout, anti-stiction measures were introduced that reduce the contact area during collapse. To improve device characterization as well as the feedback link between simulation and fabrication, a set of test structures called VM-TEST was developed to accurately determine the important mechanical material properties of thick electroplated layers. These structures utilize the measurement of the pull-in voltage in cantilever and fixed-fixed beams, along with measured structure dimensions, to accurately extract the mechanical properties. Both nickel and gold test structures were analyzed with extracted Young’s modulus values of 186.2 and 60.8 GPa respectively. Also presented is a study of the gap shape in cantilever and fixed-fixed beams that significantly reduces the pull-in voltage while still maintaining a required maximum actuator displacement. It was shown that in the case of cantilever beam actuators, an approximately 40% reduction in pull-in voltage is possible, and in the case of fixed-fixed beam actuators, an approximately 30% reduction is possible by simply varying the shape of the gap between the beam and actuator electrode. These results can be used to significantly reduce the pull-in voltage of future designs. These promising results show that the LIGA fabrication process is capable of producing high performance dynamically operating RF MEMS devices, by exploiting the vertical dimension, not typically performed in most existing RF MEMS designs.

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.

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.