AAU-ETD :: Browsing by Author "Murad, Ridwan (PhD)"

Browsing by Author "Murad, Ridwan (PhD)"

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Comparative Analysis of Blind Spectrum Sensing Techniques over Fading Channel
(Addis Ababa University, 2018-12) Milkias, Hailu; Murad, Ridwan (PhD)
A spectrum is a scarce and precious natural resource and a matter of concern with the rapidly growing wireless communications. However, studies show that licensed spectrum is underutilized. Cognitive radio system allows unlicensed users also called secondary users to access licensed spectrum band also known as spectrum hole of primary user when they are not occupied. To do this the secondary users need to continuously monitor the licensed user’s activity to find the unused band. Spectrum sensing is the key task for cognitive radio which prevents the unwanted interferences with authorized users to recognize available radio spectrum and enhance the usage of spectrum. Spectrum sensing is also a tough task because of shadowing, fading, and time-varying nature of wireless channels. This thesis investigates the difference in performance of energy detection and eigenvalue based blind spectrum sensing techniques (without having prior knowledge) by implementing it over different environmental models and compares the Receiver Operating Characteristics (ROC) curves. Evaluation and analysis of performance is done by using Monte Carlo method with MATLAB software. The implementation gives detail comparison between blind spectrum sensing technique performances over fading channel and multiple network nodes. In particular, the result shows the minimum required energy level for optimal detection (with acceptable interference) over fading channel and also how effectively cooperative
Comparative Analysis of Non-Blind Algorithms on the basis of Sidelobe Level for Smart Antenna System
(Addis Ababa University, 2018-07) Seid, Ahmed; Murad, Ridwan (PhD)
From time to time the need for good quality communication is required in different aspects of life. Many challenges can face service providers for implementing different communication facilities. One of these great challenges is the limitation of available radio frequency. So it is mandatory to use the scarce resource most efficiently in parallel with providing good quality of service for the customers. One of the way, for efficient utilization of limited radio frequency (RF) spectrum is to use smart antenna system. Smart antenna radiates not only narrow beam towards desired users exploiting signal processing capability but also places null towards interferers, thus optimizing the signal quality and enhancing capacity. The efficiency of the smart antenna can depend on different parameters like angle of separation between the desired and the interferer signal, the number of elements of the array and the spacing between the array elements. Different researches showed that the performance of smart antenna can be improved by using an array with a relatively large number of elements having an optimum spacing between them with a relatively large angle of separation between the desired and the interferer signal. The central aim of this thesis work is comparing the performance of smart antenna in terms of reducing radiation in unintended direction. This is achieved by using an algorithm that produces lower sidelobe level in the radiation pattern of the antenna. Comparative analysis of three nonblind algorithms, Least Mean Square (LMS), Sample Matrix Inversion (SMI) and Recursive Least Square (RLS), on the basis of Sidelobe Level (SLL) is studied in this thesis work. Smart antenna incorporates these algorithms to calculate complex weights according to the signal environment. Simulation results reveal that all the three algorithms have their own beamforming characteristics. But the LMS produces lower sidelobe level as compared to the other two algorithms. Therefore, the LMS algorithm is found the most efficient because of its simplicity, lower complexity and sidelobe level for communication through a flat fading channel. In addition, as the number of elements increases, the sidelobe level of array factor pattern decreases for the case of LMS algorithm.
Cooperative Communication in Mobile Ad-hoc Networks Using DSR Protocol
(AAU, 2016-05) Mosisa, Ebsa; Murad, Ridwan (PhD)
A mobile Ad-hoc network (MANET) is consists of mobile platforms which are simply referred to as "nodes" which are free to move about arbitrarily without requiring centralized administration or fixed network infrastructure. The nodes may be in or on airplanes, ships, trucks, cars, perhaps even on people or very small devices, and there may be multiple hosts per router. Through cooperatively forwarding packets for each other, nodes in mobile Ad-hoc networks can communicate with other nodes out of their direct transmission ranges. MANET nodes are equipped with wireless transmitters and receivers using antennas which may be omnidirectional (broadcast), highly-directional (point-to-point), possibly steerable, or some combination thereof. In many situations, such as military or emergency applications, nodes in an Ad-hoc network belong to the same authority and pursue the common goals. Under such circumstances, fully cooperative behavior, such as unconditionally forwarding packets for each other, can be assumed. We refer to such Ad-hoc networks as cooperative Ad-hoc networks. The common theme of most research in this area is to optimize physical layer performance measures without considering in much detail how cooperation interacts with higher layers and improves network performance measures. Because these issues are important for enabling cooperative communications to practice in real-world networks, especially for the increasingly important class of mobile Ad-hoc networks. Cooperative routing technology can efficiently improve the performance of the network by initiatively selecting cooperative nodes to forward the data. In this research, cooperative routing algorithms is proposed and implemented in mobile Ad-hoc networks and the performance of the proposed cooperative Ad-hoc algorithms are compared with noncooperative Ad-hoc dynamic-source-routing (DSR) protocol using the network simulator (NS2).
Cross Boarder Interference on UMTS Mobile Network and Its Impact on Revenue: the Case of Border Town Togowchale
(Addis Ababa University, 2018-11) Hagere, Demessie; Murad, Ridwan (PhD)
Universal Mobile Telecommunications System (UMTS) which has been standardized by the 3rd Generation partnership project (3GPP) organization, utilizes Wideband Code Division Multiple Access (WCDMA) as radio access technology. UMTS are designed to meet the increasing demands for high data rate applications and greater mobility. High data rate applications include voice, video telephony, Video streaming, File Transfer protocol (FTP), high quality image and wireless internet access. But there are many factors like loading of cell, interference etc. that limits to access these high data rate services or limits the capacity of the systems. The uplink channel is, by nature, an interference-constrained multiple-access channel. Cross border interference is caused due to the usage of the same set frequencies between two adjacent boundaries of different operators. This is the case where other operator locates their base stations in close proximity in order to provide comparable coverage to their customers. This thesis attempts to identify cross boarder interference, analysis to its impacts to the uplink capacity of all service in UMTS systems and loss of revenues is presented. The work starts with UMTS overview and learn some important concept about UMTS uplink channel interference. Then go deep into uplink channel capacity and apply the two load analysis methods to estimate the capacity loss. In the end revenue is calculated using the tariff incurred for each types of service. Ethio telecom can use this research to gain a better understanding of the problem in order to plan a strategy required to be profitable. The results described in this thesis will be a valuable contribution towards the awareness of how interference of another operator’s network (which we can’ t control) affects the performance of the network elements at boarder town.
Dual Band UMTS Network Energy Saving using Base Station Sleeping Mode: The Case of ethio telecom
(Addis Ababa University, 2019-12) Netsanet, Fekadu; Murad, Ridwan (PhD)
Base stations represent the core contributor to the energy consumption of a mobile network. Since traffic load in mobile networks significantly fluctuates during a day and night time, it is important to quantify the influence of these variations on the base station energy consumption. Therefore, this thesis proposes energy-saving technique to reduce energy consumption at the base station level. One of the approaches is the base station sleeping technique which takes advantage of varying traffic patterns on a daily or weekly basis and selectively switches some lightly loaded base stations to the sleep mode. Various literatures have investigated the potential of energy-saving technique. However, those studies have made a simplifying assumptions that leads to inaccuracy in overall results. This thesis considers the effect of trafﬁc load on energy consumption instead of making assumptions. Ethio telecom deployed UMTS network on two separate frequency bands: 900MHz and 2100 MHz. While applying energy-saving techniques, data service and radio coverages provided by the remaining active base stations need to guarantee the requirement over the whole area at all times. To this end, optimization of the SINR value of the coverage area is carried out by considering received signals of the base stations using genetic algorithms. As input data, real traffic statistics are used on a fully operated base station traffic load along with its power consumption. The tools utilized for analysis include MATLAB, MapInfo and WinProp. Performance results show that the proposed energy saving technique and algorithm can achieve energy savings of up to 25%, corresponding to the annual reduction of over 2,520 KWh per-site. Considering the selected case study area of ethio telecom mobile network, the use of energy-saving solutions allowed annual savings of more than 73,990.00 Birr per 12 square kilometers.
Enhancing Mobile Banking Service Availability Using Machine Learning
(2018-10) Said, Ahmed Said; Murad, Ridwan (PhD)
One of the main obstacles for adoption of mobile banking is that of security concern. This concern is becoming a reality in the case of mobile core inter-node protocol, Signaling System number 7 (SS7). SS7 was developed with the assumption of trusted network within and among operators. With growing number of value-added service providers and roaming partners connecting to operators, the trusted network is no longer a closed network. Attackers continue to exploit vulnerabilities of SS7 network to conduct attacks that compromise confidentiality, integrity and availability of mobile banking users and mobile network operators. In Ethiopia, Short Message Service (SMS) and Unstructured Supplementary Service Data (USSD) are mainly used for mobile banking. These services are both vulnerable to availability attacks. This thesis is an effort to detect SMS availability attacks on Mobile Application Part (MAP) layer of SS7. To mitigate these attacks, machine learning techniques using real SMS traffic data from ethio telecom is used for adaptive detection of abnormal SMS. A novel approach of using aggregation of Message Origination (MO) error codes is proposed for class feature extraction. A combination of expert judgments, literature reviews and information gain are used for optimal feature selection. As a result, it is recommended to use origination, destination, and mobile switching center address and write time as optimal features. To solve the problem of attack message detection, PART, Random Forest and J48 algorithms are compared. It is found that J48 has a superior performance with an accuracy of 98.6465% and model build time of 3.71 seconds.
Feasibility Study on Aircraft Location Accuracy Using Multilateration System in the Case of Addis Ababa Bole international Airport
(Addis Ababa University, 2021-12) Kibreab, Kibebew; Murad, Ridwan (PhD)
The aviation sector must be safe. Information errors which are provided from ground aids Communication, Navigation and Surveillance (CNS) systems can put the aircraft at risk. Therefore, all ground-based flight aids should always be accurately calibrated. In addition, flight delays can lead to unnecessary fuel consumption and air pollution. Accordingly, in order to provide an efficient air transport system, it is important to have modern, fast and accurate ground based flight aids that provide real and timely information. Air Navigation Aeronautical multilateration systems enable the localization of an aircraft based on the Time Difference of Arrival (TDoA) of its signal to three or more strategically placed receiving ground station antennas, located around an area of interest, providing continuous air traffic surveillance. The main objective of this thesis is to show how to install an optimized multilateration system that can provide an aircraft information (position & identification) and to study the performance analysis of approach type multilateration systems in Ethiopia, specifically in Addis Ababa Bole international airport approach and terminal maneuvering area concerning radio coverage and aircraft location accuracy by considering ground stations’ location, their antennas radiation patterns, transmitted power, receiver sensitivity, and the corresponding parameters for the aircraft. Line of Sight situation is assessed by taking into considerationof Digital Elevation, Fresnel’s Ellipsoid, and the Effective Earth’s Radius Models. The Free-Space Path Loss Model is likewise used, with fading margins being set to model power oscillations due to multipath and the airplane orientation uncertainty. The position accuracy of the aircraftis estimated from the system’s Geometric Dilution of Precision, taking into considerationof error components due to troposphere delay, multipath, receiver noise, quantization, and clock bias. The model will be implemented in a simulator with results in agreement with data from the literature and previously implemented systems.
Geolocation of Narrow Band Radio Frequency Emitter Using RSS based Localization Techniques: The Case of Addis Ababa
(Addis Ababa University, 2021-09) Kebe, Adugna; Murad, Ridwan (PhD)
Currently, determining the coordinate of fixed or moving objects using propagation features of radio waves such as signal strength, propagation delay, signal phase, and angle of arrival have been a subject of interest in radiodetermination. Radiodetermination can be categorized into radiolocation, ranging, and radio navigation. Ranging is to estimate the distance between the receiver and the transmitter. Radiolocation (geolocation for the object on the earth) predicts the position of an object. Radio navigation encompasses both ranging and radiolocation. Triangulateration and trilateration (range-based) techniques use for radiolocation purposes. Triangulateration technique relies on line of bearing from receiver to emitter incorporating with antenna arrays. Whereas, Trilateration considers received signal strength (radio-wave propagation path loss models) and propagation delay. Following radio wave properties and applied technologies, measurements have been taken by deploying radio wave measurement systems on the ground, or in aircraft. In this thesis, passive radio frequency (RF) emitter geolocation was analyzed by considering received signal strength (RSS) techniques to compare and analyze the performance of RSS-based geolocation techniques and algorithms. For this purpose, data were gathered using a mobile radio spectrum monitoring unit (receiver), and it was analyzed using software tools such as excel and Python. Radio wave propagation is statistically modeled using the lognormal shadowing model and regressive methods to determine the distance. The results indicate that the error of estimated distance with regressive and clustering approach on average by 96% over the non-clustered approach. With this approach, weighted least square (WLS) estimates location with the error of 170 meters, whereas linear least-squares (LLS) estimate with the error of 206 meters. The lognormal model estimates distance with a minimum error than the regressive method when the standard deviation of data is less than 2dB. At the end, there is a positive correlation between estimated distance and location. It means the error of estimated location increases, as the error of estimated distance increases.
Investigating of SU-MIMO Techniques for LTE- Release 8 in Highly Scattering Environment
(AAU, 2017-07) Nebiyu, Suleyman; Murad, Ridwan (PhD)
LTE systems promise of delivering large data rate to users which is substantially larger than what the previous third generation (3G) systems offered. However, as user traffic grows it will put greater demands on network capacity. More importantly, in urban environment the construction of buildings, which are taller than base station’s height, create highly scattering environment for radio signal which leads to multipath fading. Small antenna height has in turn negative effect on both coverage and capacity. Multiple Input Multiple Output (MIMO) antenna systems are one of the most efficient leading innovations to accommodate high data traffic and eliminate the effect of multipath scattering environment. MIMO systems can turn multipath propagation, traditionally a pitfall of wireless transmission, into a benefit for the user. It can also be used to achieve improved system performance, including improved system capacity and improved coverage, as well as improved service with higher per-user data rates. The operator can achieve all these without increasing average transmit power or frequency bandwidth. This thesis investigates the performance evaluation of different schemes of Single User MIMO (SU-MIMO) for the downlink of LTE. This evaluation will be based on performance metrics such as ergodic capacity and average Bit Error Rates (BER) for different MIMO antenna transmission schemes and their tradeoff. For this case study, the ideal MIMO radio channel models assume a Rayleigh fading environment which is used as a reasonable model for the effect of heavily built-up urban. It will be shown analytically and with MATLAB simulation the impressive improvements in capacity and BER brought about by the use of SU-MIMO techniques. Finally suggestion will be given to which modes of MIMO to use for different kind of highly scattering environment depending upon the speed (fast and slow moving) and location (cell-centered and cell-edge) of the user equipment (UE). The developed techniques can be applied to fast and accurate performance evaluation for future network planning, deployment and optimization of LTE-MIMO systems.
Minimization of Coupling Loss in Micro strip Antenna Arrays Using Defected Ground Structure & Frequency Selective Surface
(Addis Ababa University, 2021-04) Leyla, Ahmed; Murad, Ridwan (PhD)
The performance of microstrip antenna arrays is greatly undermined by the excitation of space waves and surface waves which cause mutual coupling between microstrip antenna elements. Mutual coupling between antenna elements can affect the side lobe levels, beam position and frequency bandwidth of arrays. Mutual coupling through space waves are very strong if the array elements are very close to each other, and they can be suppressed by increasing the interelement spacing between the array elements. Defected ground structure (DGS) is a type of metamaterials designed at ground that is used to minimize the surface wave and prevents the degrading in performance of an antenna. Frequency Selective Surface (FSS) is also useful in miniaturization of a designed antenna. In this thesis work, a ground plane is loaded with defected ground structure and frequency selective surface techniques to minimize the effect of coupling loss and to enhance the performance of the MSPA. A rectangular-aperture coupled microstrip patch antenna is first designed for S-band application and 2x1 MSPA antenna array is formed by using the optimized design of the individual antenna for an inter element spacing l/4 (where l is the operating wave length of the antenna which is equal to 130.43mm). Then a simulation is carried out to measure the S11, S12, and other parameters of the antenna. Finally, DGS &FSS are applied on the antenna and the reduction in coupling loss is analyzed using HFSS Software. The result of the study indicates, 2X1 rectangular micro strip patch antenna array inserting FSS at the ground plane were proposed for 2.3GHz which has an improved bandwidth of 71.8MHzand mutual coupling effect is -35.668dB when compared with an antenna array with DGS.
Modeling GSM Spectrum Occupancy Using Time Series Analysis: The case of Ethio telecom
(Addis Ababa University, 2021-09) Anteneh, Atnafu; Murad, Ridwan (PhD)
Spectrum occupancy models can help you make better use of the radio spectrum. It has also been extensively researched in recent decades as it is critical for developing new regulations for spectrum allocation for future technologies as well as monitoring the activities that take place on that spectrum. Understanding the amount of available spectrum is critical for future wireless technologies that want to address the so-called spectrum scarcity issue. Spectrum occupancy measurements provide critical data for frequency planning and optimization, as well as assist in smart decision-making. The goal of time series modeling is to collect and thoroughly examine previous data from a time series in order to construct an appropriate model that accurately captures the series’ intrinsic structure. This thesis examines three types of time series analysis methods: Holt-winters, Seasonal Auto Regressive Integrated Moving Average (SARIMA), and SARIMA eXogenous regresses (SARIMAX) based models, as well as their inherent prediction strengths and weaknesses. Time series modeling principles such as trend, stationarity, seasonality, residual, and so on have also been covered. To assess the accuracy rate, we fitted multiple models to a time series using five primary metrics. Among the methods used are mean square error, mean absolute error (MAE), root-mean-square error, mean absolute percentage error, and R-squared. At 1800MHz, the maximum spectrum occupancy is 60.35%, and at 900MHz, it is 44.71%. For 900MHz MAE, the SARIMAX model produced better predictions (35.34% and 50.1% lower than the SARIMA and Holt-Winter models, respectively), while for 1800MHz, the SARIMAX model produced 42.6% and 52.6% lower than the SARIMA and Holt-Winter models, respectively
Parametric Study and Performance Analysis of PIFA Array Antenna At Ka-Band
(AAU, 2018-07) Behailu, Gobanti; Murad, Ridwan (PhD)
Planar inverted F-antenna are playing an important role in wireless communication systems because of their many advantages like light weight, low profile, low cost, easy integration with planar structure and easy fabrication. The main objective of this thesis is to discuss the characteristics of PIFA antenna using different change of design parameters such as shortening plate width, ground plane width ground plane length, patch width, and patch length and height. The design issues include PIFA antenna dimensions, feeding techniques and various polarization mechanisms whereas the performance issues include voltage standing wave ratio, radiation pattern, directivity and specific absorption rate. In this thesis, both single element and four by four elements of PIFA antenna at Ka-band are designed using the CAD-FEKO simulation software. To design it, standard formulas are used to calculate different parameters of the antenna. The proposed antenna is designed to work at 28GHz frequency band and simulation results shows that 4.66 dB and 7.63dB of directivity for single element and four by four elements of PIFA antenna were attained respectively and also SAR values of 2.26w/kg for single element and 0.613w/kg for four by four elements design were attained. To achieve all the above results both single element and planar array of PIFA antenna were designed with micro-strip line feeding based on quarter wave impedance matching technique using CAD-FEKO simulation software.
Performance Analysis of Linear Precoding for Multiuser Multiple-Input and Multiple-Output Broadcast Channels
(Addis Ababa University, 2023-09) Worku, Tamene; Murad, Ridwan (PhD)
Multiuser Multiple Input and Multiple Output is an antenna technology for wireless communication in which number of users or wireless terminals each with one or more number of antennas communicate with each other. Precoding in multiuser MIMO systems is important to minimize or mitigate the multiuser interference. As a consequence, the design of suitable precoding algorithms with a low computational complexity and a good overall performance is a challenging scenario when system dimensions are high. A linear precoding technique such as regularized channel inversion (minimum mean square error), channel inversion (zero forcing), and Block diagonalization techniques for multi-user multiple input multiple-output broadcast channels are able to eliminate the multiuser interference per antenna or sum power constraint. After conducting this thesis an enhanced performance is measured from this thesis. In case, analysis of the MU-MIMO with fewer number of antennas may reduce the cost of antenna and some complexities in large antenna system. Different researches are conducted in multiuser MIMO with single antenna receivers and conducted mostly in Rayleigh channel conditions. Besides, the performance of multiuser MIMO linear precoding under different channel conditions together with two or more antenna receivers have been investigated in this work. In this research, the performance of linear precoding in multiuser MIMO under Rayleigh, Rician and Deterministic channel conditions are illustrated in different performance metrics like data rate, channel capacity and spectral efficiencies. The performance of linear precoding under multiuser MIMO with two antenna users have a great performance due to the combined effect of the antennas. In addition, the Rican channels achieves minimum bit error rate than Rayleigh and deterministic channels. Furthermore, this study has advantage of detail comparative analysis when the users are more, and this analysis have a direct impact when the congested number of users are involved.
Performance Analysis of Printed Array Antennas for 5G Mobile Communications
(Addis Ababa University, 2021-10) Muzey, Tsigab; Murad, Ridwan (PhD)
Nowadays with the limited spectrum bands the mobile operators have been challenged to deliver multimedia applications with higher data rates, low latency and better quality of service of mobile communications to a growing number of users. This has led to a big number of inventions and technology advancement in past decades which is the prime goals of the upcoming 5th generation (5G) mobile networks. The millimeter wave (mmWave) is a suitable candidate for 5G with its high frequency range from 30 GHz up to 300 GHz. This thesis aims to design, analyze, simulate and compare the single and array elements of printed dipole, microstrip patch and planar inverted-F (PIFA) antennas regarding to their performances at the same operating frequency of 28 GHz using computer simulated technology (CST) microwave studio electromagnetic simulator. The comparison is based on simulated results of radiation pattern, gain, directivity, VSWR, return loss and e ciency. Based on the results obtained 4 1 array antennas have maximum gain and directivity of 9.87 dBi and 10.12 dBi for printed dipole antenna, 12.09 dBi and 12.37 dBi for microstrip patch antenna, and 9.79 dBi and 9.812 dBi for PIFA, respectively. The VSWR and return loss value, respectively, is found to be 2.4 and -7.57 dB for printed dipole array antenna, 1.09 and -27.37 dB for microstrip patch array antenna, and 2.6 and -6.5 dB for array of PIFA. The radiation e ciency for printed dipole array antenna is -0.248, for microstrip patch array antenna is -0.275, and for array of PIFA is -0.18. In this regard, the analysis shows that the microstrip patch antenna is quite capable of achieving the highest performances and represent an obvious choice for mobile applications. Moreover, to achieve an optimum design parameter the microstrip patch array antenna is also simulated with varying values of the substrate height, substrate thickness, patch length and patch width. The e ect of these parameters on antenna performance is analyzed.
Planning Efficient Microwave Link for EBC (Main Studio)
(AAU, 2018-06) Berhanu, Teshome; Murad, Ridwan (PhD)
Microwave links play an important role in the broadcasting industry by linking main radio and television studios with remote transmitter stations. With the currently increasing number of locally and internationally broadcasted television and radio stations the need for such links is expected to increase significantly. Furthermore, the expected links are also required to overcome the dynamic nature of the country’s main cities. To emphasize on the matter, the country’s main broadcasting corporation, i.e., Ethiopian broadcasting corporation (EBC), can be taken as an example. The corporation currently utilizes microwave links for transmission of programs from production studios to transmitter station and also from the temporary outside broadcast (OB) studios to main head office studios. But due to topological nature of Addis Ababa and intensive constructions of new tall buildings microwave links have become one of the many reasons for most live television broadcasting failures. Overcoming the stated problem on locally existing microwave links requires a careful planning and analysis that are in phase with the dynamics of the cities. This thesis thus provides a solution for improving the quality of microwave links that are currently utilized by Ethiopian Broadcasting Corporation (EBC). To accomplish the task, three frequently utilized microwave link sites, located at Addis Ababa stadium, Janmeda, and Millennium hall, are selected. Afterwards, planning and antenna height selection for repeater stations were performed. Based on the planning ten repeater sites are found to be in line of sight to the temporary stations. Finally, the quality of established link between the repeaters and temporary studios were analyzed using a simulation software namely Radio Mobile. The analysis has shown that, as compared to existing microwave links the proposed solution improved field strength by 61.66% and fading margin by 64.44%. Furthermore, out of selected repeater sites Gomakuteba is found to be the best links for Janmeda & Milinim Hall whereas Legehar for Stadium. In general, the thesis has set preliminary results that are found to be promising.
Side Lobe Suppression in Linear Polarized Antenna Arrays
(Addis Ababa University, 2020-01) Zewdie, Ayalew; Murad, Ridwan (PhD)
Side lobe suppression is one of the most important design considerations of linear antenna array to reduce interference and wastage of radiation power. Side lobe level reduction also avoid indicating false target. The reduction of side lobes can be achieved by proper calibration of inter element spacing, excitation amplitude or both inter element spacing and excitation amplitude at a time. In addition to these commonly used methods of side lobe suppression, changing the orientation of selected elements by rotating them about the normal of the array axis can change the polarization of the element pattern. This technique can produce polarization variation as compared with uniformly oriented elements. The purpose of the rotation of elements is to create interference in the side lobe direction of non-rotated array elements. Due to this created interference, the side lobe level of the whole array can be suppressed. This thesis presented side lobe level suppression of linear antenna arrays employing rotation of array elements. Simulations were performed using MATLAB and genetic algorithm optimization tool has been used to find angle of rotation, inter element spacing and excitation amplitude. Employing rotation of symmetrically positioned array elements, side lobe levels of -17.15dB for uniformly spaced & uniformly excited linear array, -20.40dB for non-uniformly spaced & uniformly excited linear array, -27.25dB for uniformly spaced & non-uniformly excited linear array and finally -28.02dB for non-uniformly spaced & non-uniformly excited linear arrays have been obtained, as can be seen on result, for a total of 10 array elements. As compared to radiation pattern of uniform linear arrays without rotation of elements, the obtained results show significant reduction of side lobe level. As a result of this side lobe reduction, energy wastage and interference outside of the main beam can be minimized with considerable amount and the performance of the array can be improved.

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