Theses & Dissertations

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https://hdl.handle.net/20.500.14170/209

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Now showing 1 - 5 of 156
  • Publication
    Three-dimensional printed horn antennas with dielectric lens for free-space constitutive parameters measurement
    ( 2024)
    Renukka Sivakumar
    Over the last two decades, there has been significant development in mm-wave and terahertz (THz) technologies, driven by their appealing properties in various applications, including automotive paint materials, metamaterial structures, radio astronomy, military, and medical field. Additionally, the use of dielectric properties for material identification has proven valuable in mm-wave imaging systems. As a result of the increased demand for mm-wave components and systems, there is a greater need for cost-effective measurement solutions in this frequency range and beyond. The free-space measurement technique is widely used methods for determining the electrical characteristics of materials. This doctoral research aims to focus on the development of a free space material measurement system capable of accurately determining materials' permeability and permittivity. A software program through modified NRW algorithm which could determine the materials’ permeability and permittivity with high accuracy was developed rather than expensive commercial software. Also, the permeability and permittivity of MUTs were determined with high accuracy through the software with and without lens for the commercial horn antenna and 3-D printed horn antennas. High gain K-band and Ka-band horn antennas from 18 GHz to 39 GHz using 3D printing technology were designed in order to overcome the need for costly commercial measurement systems. To mitigate the measurement inaccuracies, 3-D printed dielectric lens was designed and fabricated through 3-D printing technology in which beam focus of antenna optimized. 3-D printed horn antennas showed a good agreement with the commercial horn antenna in terms of S11, VSWR, gain and 3- dB beamwidth. As for the gain, with the use of lens the gain increased with a maximum gain of 25.7 dBi at 26 GHz when compared to the gain without the use of lens with a maximum gain of 15.6 dBi at 26 GHz for the K-band horn antenna. Also, for the gain, with the use of lens the gain increased with a maximum gain of 26.5 dBi at 32 GHz when compared to the gain without the use of lens with a maximum gain of 15.5 dBi at 32 GHz for the Ka-band horn antenna. Without the use of lens, 3- dB beamwidth is in the range of 33º to 41.5º while with the use of lens, the 3- dB beamwidth is in the range of 8.9º to 9.7º for the K-band horn antenna. Use of lens allows narrowed beamwidth which focus signals in particular direction throughout the K-band frequency range. As for the Ka-band horn antenna without the use of lens, 3- dB beamwidth is in the range of 28º to 50º while with the use of lens, the 3- dB beamwidth is in the range of 7º to 9º. As for the E-field distribution for the dielectric lens, it increased as the frequency increased which is from 549 V/m at 18 GHz to 855 V/m at 26 GHz for the K-band horn antenna. As for the Ka-band horn antenna, the E-field distribution for the dielectric lens increased from 855 V/m at 26 GHz to 941 V/m at 39 GHz.
  • Publication
    Characterizations of multiwavelength brillouin fiber laser by utilizing semiconductor optical amplifier in single and double nonlinear optical loop mirror
    ( 2021)
    Siti Noraini Che Abdul Jalil
    This thesis demonstrated the research work on the multi-wavelength Brillouin fiber laser by utilizing semiconductor optical amplifier in single and double nonlinear optical loop mirror configuration. By exploiting the stimulated Brillouin scattering effect and the used of a semiconductor optical amplifier placed in the loop mirror able to increase the performance of the signals. It has the potential to amplify and increase the output number of signals that pass through the fiber link, particularly in dense wavelength division multiplexing systems. The research begins with the investigation on two different of the gain medium used in the configuration such as single-mode fiber and dispersion compensating fiber. Meanwhile, the generation number of signals was analysed based on four different injection currents of semiconductor optical amplifier at 0.5 A, 0.6 A, 0.7 A and 0.8 A with different fiber lengths from 5 km to 15 km. Therefore, the results from the study indicate that utilizing dispersion compensating fiber at 13 km length with maximum semiconductor optical amplifier current at 0.7A generated more than 30 output signals. Henceforward, comparisons have been made by utilizing single-mode fiber to replace the dispersion compensating fiber in the loop mirror configurations. The use of dispersion compensating fiber at 6 km and 0.8A of maximum semiconductor optical amplifier current able to generate 11 output signals. The higher injection current of semiconductor optical amplifier at a shorter length of single-mode fiber capable to generate more output number of signals. In conclusion, the parameter of different injections current at semiconductor optical amplifier and fiber length of the gain medium plays a vital role in producing the output number of signals. Next, the studies expanded into a double nonlinear optical loop mirror configuration whereby consists of two devices of semiconductor optical amplifier located in each loop mirrors. The 6km length of single-mode fiber also placed in the loop mirrors. Onward, the characterization based on the effect of injected Brillouin pump power into configurations with a different range from -12 dBm until 12 dBm was demonstrated. The comparison had been made between single and double nonlinear optical loop mirrors. As a result, the double loop mirror able to provide more output number of signals when utilized low level of input Brillouin pump power at -8 dBm. The average optical signal to noise ratio was recorded at ~26 dB by utilizing lower input Brillouin pump power at -11 dBm. Meanwhile, the single nonlinear optical loop mirrors configurations able to produce more output number of signals at high input Brillouin pump power. At 5 dBm, 6 dBm and 7 dBm of input Brillouin pump power, can produce an 11 output number of signals, respectively. Therefore, the higher average of the optical signal to noise ratio was observed at ~22.2 dB by utilizing 8 dBm of input Brillouin pump power. The result can be seen clearly at the end of the thesis whereby utilizing a semiconductor optical amplifier to generated multi-wavelength signals able to increase the performance of the fiber laser system. Furthermore, the nonlinear effects involve in the configuration also play an important role in fiber laser system.
  • Publication
    Development of RTL platform validation methodology for customized wireless microcontroller unit
    ( 2021)
    Nurul Zhafirah Muhammad
    Demand for customized wireless microcontroller unit (MCU) has been expanding due to the requirement of end-to-end IoT solution, product requirement, and potential IP. As such, the development for design complexity growth poses by the evolution of the SoC technology, causing the issue of time spent in the area of validation has increasing for the newly complex design developed. Thus, this research was highlighted on the RTL Platform Validation methodology by utilizing the existing method for newly developed MCU to overcome the time spent on the validation. As the goal of this research to find the fastest method that can be customized to the current MCU design, hence this RTL validation were divided into two levels which were module level and system level. For module level, the verification was focused on the IP’s source code. Thus, in this module level, the simulation-based method, which is code coverage technique was utilized and being implemented in white box environment as to verified the quality of the codes and to obtain the maximum reasonable coverage to be covered. For this MCU system, the reasonable coverage that needs to be obtained at the module level was more than 80%. The advantage of the code coverage technique was the bugs and errors of the design can be detected at the early stage. As if the IP only achieves the targeted coverage than will move to the next level of verification, which is system level. Otherwise, the IP design was declared as unsuccessful and resulting to redesign as specified. Meanwhile, for system level, the verification was based on the implementation of test bench as to verify the system with a set of test vector. The detailed on the techniques used and the results of this research were presented in the thesis.
  • Publication
    Mutual coupling reduction between pattern reconfigurable antenna arrays using electromagnetic band gap
    ( 2024)
    Jaya Bharath Gopalakrishnan
    Antenna is a widely used device in wireless communication system to transmit and receive the electromagnetic wave. Sometimes the antenna faces difficulties to perform well with signal reception because of the interferences caused by the unwanted signals. To overcome this problem, the radiation pattern reconfigurable (RPR) antennas have been widely used. This antenna has a capability to alter the radiation pattern which steers towards a desired signal. On the other hand, due to increasing of high demand from the user, researcher came out with multiple-input-multiple-output (MIMO) antenna. This is because, in earlier time the internet and data usage are still new, thus the demand was not high. However, in this new era of technology the internet and data usage increase tremendously and have improved without a limit. Most of the existing research focuses on frequency reconfigurable MIMO antenna that specifically used for mobile terminal application. Limited studies were conducted regarding pattern reconfigurable MIMO antenna. The mutual coupling caused by MIMO system may not only affect the S21 performance, but could further affect the beam steering performance of the RPR antenna. A comprehensive analysis is conducted in the proposed work to identify the challenges of implementing the RPR antenna as MIMO. Hence, this thesis mainly focuses on the following: analyze the beam steering performance of RPR antenna when implemented as MIMO; and to reduce the mutual coupling effect towards the beam steering performance, an hexagonal split ring resonator (SRR) electromagnetic band gap (EBG) is proposed. First, to enhance capability of the antenna to serve more users the RPR antenna is implemented as MIMO, taking RPR-MIMO as the design name. The RPRMIMO antenna is designed to operate at 3.5 GHz with S11 < -10 dB, S21 < -15 dB, steered angle of more than 20° and minimum average gain of 5 dBi at all steered directions. The RPR-MIMO was modelled in, three configurations, namely configuration 1, 2 and 3. From analysis, configuration 3 was identified that gives minimal effect to the RPR beam steering performance and mutual coupling in terms of S21. On the other hand, the proposed SRR-EBG produced band-gap region from 3.3 GHz frequency to 3.6 GHz frequency. The EBG based RPR-MIMO (RPR-MIMO-EBG) helps to improve the steering angle. Then DC biasing was applied to the RPR-MIMO-EBG antenna before fabrication was carried out. The experimental verifications have demonstrated that the measured results agree well with the simulation. The future work may consider implementing the embedded system with the proposed RPR-MIMO to monitor and track the high demand of network user and will serve toward accordingly.
  • Publication
    Design and development of scheduling algorithms for downlink transmission system of Long Term Evolution (LTE) network
    ( 2015)
    Normaliza Omar
    In today‟s technology development, people need internet access wherever they are, mobile broadband will grow up actively. Therefore, service providers gradually compete to produce the maximum internet speed for public uses. To enable high-speed data services to mobile users, scheduling technique gained significant attention in wireless access networks. A feature of the wireless environment is that the quality of the different channels of the user population due to a conflict path loss and effect of the attenuation. The best scheduler should provide high throughput, low latency system and the best coverage gains. In order to develop the best scheduling, the scheduler must be aware of the channel quality and scheduler should have associate of the channel quality for each sub carrier and each user. In order to exploit the diversity of multiuser in addition to deliver further compliance in resource allocation, an algorithm is proposed in this work where system latency is considered as the first priority in scheduling steps and followed by arrangement of user equipments (UEs) according to the Channel Quality Indicator (CQI) scheduler for Long Term Evolution (LTE) structure. The analysis and the comparison of these scheduling algorithms were prepared over simulations done by a MATLAB-based downlink system level simulator from the Vienna University. The main target in this thesis is to propose a new scheduling for resources allocation that may be compromise between throughput and fairness to avoid useless space in a scheduler. Useless space may cause the latency that may cause of delay in transmission. The Round Robin (RR) scheduler and best CQI scheduler are considered in this research work. There are two (2) enhanced scheduling algorithms proposed in this research work which are Resource Fairness (RF) and Maximum Throughput (Max TP) scheduling algorithm. The enhanced scheduling algorithms have been proposed based on Proportional Fair (PF) scheduling algorithm. PF is one‟s of scheduling algorithm that have compromise between throughput and fairness. From the observation, it shows that RF scheduling algorithm has been achieved about 19% of improvement in term of fairness index compared to other scheduling algorithm for all type of network scenarios. While Max TP scheduling algorithm has provide about 25% of improvement in term of throughput for all network scenario. Since RF scheduling algorithm provide second highest throughput value which having about 11% of improvement compared to other scheduling algorithm, it may be considered that RF scheduling algorithm has achieved high compromise between fairness and throughput compared to PF scheduling algorithm.