RESEARCH TITLE : DUAL BAND MICROSTRIP ARRAYS AND ULTRA WIDE BAND ANTENNAS WITH ELECTROMAGNETIC BAND GAP STRUCTURES
Researcher : THELAHA MASRI (PhD-GRADUATED 2009)
This research focuses on the possibilities of integrating Electromagnetic Band Gap (EBG) structures with Dual Band Microstrip Antenna’s Array (DbMSAA) and Ultra Wide Band (UWB) antenna, with an objective to further improve the antennas’ performance by reducing, if not eliminating, the limitation that they have. From the parametric study of the already established two-dimensional mushroom shaped EBG structures, novel designs of dual band-gaps EBG structures are proposed and fractal shapes were implemented to achieve the objective. As a result, guidelines, graphs and tables of the EBG structures’ designs and configurations were put forward for reference. A DbMSAA has been purposely designed to represent a problematic antenna and, through the incorporation of EBG structures via novel and innovative techniques, the performance of the antenna has been improved, upgraded and realized. The grating lobes diminished, radiation patterns become more symmetrical and its gain increased. On the other hand, UWB systems could become a jammer for the numerous licensed services if it does not comply with the regulations mandated by the Federal Communication Commission. To solve this problem, a single unit of EBG lattice is incorporated into a model of the UWB antenna to act as a ‘band stop filter’ in such a way that the radiating power is reduced to a level that will not intrude any existing channels. Finally, other filtering techniques, which seem to be much simpler such as stubs and defected ground plane (DGS) techniques were also investigated and compared to the EBG structures. Stubs could filter out and stop the targeted band of frequencies but undesirably, it upset the input impedance of the antennas, while the DGS technique is only suitable for thin substrate of less than 0.5 mm. These circumstances confirmed that the EBG structures performed better, and validate the works and concept proposed. Further research and works that needs to be carried out are also proposed in the conclusion of this thesis
RESEARCH TITLE : BROADBAND AND MULTIBAND DIELECTRIC RESONATOR ANTENNA
Researcher : MOHSEN KHALILY (PhD-GRADUATED 2010)
In recent years, dielectric resonator antennas (DRAs) have been targeted as a potential solution for wideband and multiband antennas; they provide wider bandwidth and smaller size than microstrip antennas. The problem in designing this kind of antennas is to design a smaller size broadband antenna especially at low frequencies, because the bandwidth and size of the antenna depend on dielectric resonator constant. This research investigate different methods for wideband and multiband-dielectric-resonator antennas. In the first design, a novel hybrid dielectric resonator antenna excited by a printed monopole antenna is proposed and implemented for multiband application. Measured results show that the proposed DRA can be used in multiband wireless operations ranging from 1.54 GHz to 6.2 GHz. Second design presents a new modified planar dielectric resonator antenna for wideband and multiband applications. Dielectric resonator consists of a rectangular ring-shaped, housed inside the dielectric substrate above the vertical ground plane edge. Peak gain and directivity enhancement are achieved by using only one or two narrow strips, connected to the ground plane. The measured bandwidths are about 73% (2.78~5.95 GHz) for wideband DRA as well as 8% (2.4~2.6 GHz)and 56% (3.3~5.85 GHz) for the dual band DRA. The third design presents simple and compact wideband rectangular dielectric resonator antenna. The bandwidth is enhanced using a proper tapered strip excitation from one side of the dielectric resonator and by adding a shorted narrow strip to the opposite side of the excitation. The proposed DRA with good radiation characteristics offers a measured bandwidth of 96% between 2.13 and 6.08 GHz. Finally, the fourth design is a novel P-shape dielectric resonator antenna for wireless application. Using this P-shape dielectric resonator, a wideband antenna is achieved. The prototype is fabricated and the antenna characteristics are measured. The measured bandwidth is about 80% from 3.5 to 8.2 GHz.
RESEARCH TITLE : Triple-Band Dipole Antenna With Artificial Magnetic Conductor For Radio Frequency Identification
Researcher : MAISARAH ABU (PhD-GRADUATED 2010)
The radiation characteristics and input impedance of the dipole antenna will be distorted when the antenna is placed on a metal object. The electromagnetic wave of the antenna is reflected almost entirely by the metallic surface and a 180° phase shift is occurred. In addition, a common dipole antenna has low gain which is about 2.15 dBi. Owing to the high impedance, surface structure called Artificial Magnetic Conductor (AMC) is developed as a ground plane for the dipole antenna to prevent the performance degradation of the antenna caused by metallic objects and to increase the antenna’s gain. Due to the reflected wave of the AMC is in-phase with the antenna current (reflection phase equals to zero), it improves the radiation efficiency and subsequently enhances the gain of the dipole antenna. Thus, due to the great demand in multiband antenna, this research has developed a triple-band dipole antenna with straight and meander structures at Ultra-high Frequency (UHF) and Microwave Frequency (MWF) Radio Frequency Identification (RFID) frequencies; 0.92 GHz, 2.45 GHz and 5.8 GHz respectively. Firstly, the single-band square-patches AMCs are investigated. Then, to obtain a smaller structure of AMC and suitable for RFID applications, two new structures of AMC-HIS are developed. They are single-band AMC called zigzag dipole and dual-band AMC called rectangular-patch with slotted rectangular and I-shaped slot. The parameters that affect the AMC performance are discussed and the performances of the antenna with and without the AMC GP are investigated in terms of return loss, total gain, total efficiency and directivity. From the results gained, in general the power received of the dipole antenna with AMC GP is higher than the power received of the dipole antenna with the absent of AMC GP. Furthermore, a longer reading distance is recorded for the dipole tag antenna backed by AMC structures. For instance, the reading distance for the UHF meandered dipole tag antenna with the 2x2 rectangular-patch with slotted rectangular and I-shaped slot has achieved two times higher compared with the dipole antenna without the AMC GP. While at MWF, its reading distance is increased from 0.8 m to 1.25 m. The performance of the dipole tag antenna with AMC GP attached to the metallic plate size is also tested to verify the dipole tag antenna with AMC GP can be used for metallic object detection in RFID applications.
RESEARCH TITLE : Textile Ultra Wide-Band Antennas For Wearable Applications
Researcher : MAI ABDEL RAHMAN OSMAN (PhD-GRADUATED 2011)
In wearable textile antennas, there are several objectives to be achieved to ensure the robustness and flexibility of wearable devices. This research aimed at investigating the possibilities of designing and fabricating wearable antennas where substrate and conducting parts of the proposed designs are made from textiles. Several types of fabrics for usage as antennas substrates are considered in this investigation. The dielectric properties of substrate materials are examined and measured. To study the feasibility of using fabric substrate materials, rectangular microstrip patch antenna designs are introduced and sufficiently resonated at the ISM band frequency of 5.8 GHz. Further investigations are made with the intention to achieve the objectives by designing two new Ultra Wide-Band (UWB) antennas.Conducting materials that are prominent as Electro-textiles are successfully used for conducting parts of the UWB antennas prototypes. Experiments are carried out where results reveal several scenarios. For fabric substrate materials types, flannel and jeans fabrics are tested and require further investigations, while lint and songket fabrics are considered as non-suitable choice for further investigations. Investigation indicates that flannel and jeans fabrics are recommended for stacking layer purposes. Measured results of UWB antennas using Electro-textile materials such as copper conducting fabric, Shieldit conducting fabric, and conducting thread showed comparable results with ideal copper conducting sheet results. Considering one-layer and three-stacked-layer configurations, the Electro-textile UWB antennas prototypes produces bandwidth results of more than 12 GHz and 17 GHz respectively. Results exposed that the decision on the preferable conducting material depends totally on application requirements, while each of the prototypes has its pros and cons during fabrication and measurements. The measured results of bending effects found to be not significant on textile antennas performances. This research has profound implications for future studies that may one day help to provide the wearer with reliable and comfortable wearable standalone suite.
RESEARCH TITLE: FREQUENCY RECONFIGURABLE MICROSTRIP SLOT ANTENNA (Graduated)
Researcher: HUDA A. MAJID (PhD- GRADUATED 2013)
Cognitive radio system needs a wideband antenna for spectrum sensing and a narrowband reconfigurable antenna for communication link. Presented here are frequency reconfigurable antennas which are capable for narrowband to narrowband reconfiguration and wideband to narrowband reconfiguration. These concepts are introduced to give high flexibility to a wireless terminal to operate in different bands. The proposed antennas are potentially useful for future wireless communication system such as cognitive radio. Four novel frequency reconfigurable antennas are presented and discussed. Microstrip slot technique is used as a basis for all design of the narrowband reconfigurable antennas. First, a frequency reconfigurable slot antenna is proposed to have a capability for narrowband to narrowband reconfiguration. The antenna is capable to reconfigure up to six different narrowbands from 2.2 GHz to 4.75 GHz. Second, a frequency reconfigurable slot integrated with patch antenna is proposed. The proposed antenna is capable to reconfigure into nine different narrowbands from 1.98 GHz to 3.41 GHz. Here, the omni-directional radiation pattern is introduced in slot mode while directional radiation pattern is obtained in patch mode. The third designed antenna is a monopole wideband antenna integrated with frequency reconfigurable slot antenna. This concepts offer wideband to narrowband reconfigurablility. The significant advantage of this approach is, it offers pre-filtering for the front end cognitive radio system, which reduces the interference level at the receiver. The proposed antenna has the capability to reconfigure between wideband (2 GHz - 6 GHz) and three different narrowbands from 3.02 GHz to 4.56 GHz. Finally, a frequency reconfigurable slot antenna with added function of tuneable radiation pattern is also been presented. The antenna has the ability to reconfigure three different narrowbands from 1.75 GHz to 2.1 GHz and is also capable for beam shifting at three different angles (0o, +30o and -30o). Computer Simulation Technology (CST) software is used for antenna simulation. PIN diode switches and hard wire switches are used to represent switches in the simulation and measurement. Very good agreement between simulated and measured results such as return loss, radiation pattern and gain are presented, thus verifying the proposed antennas concepts.
RESEARCH TITLE : DESIGN AND DEVELOPMENT OF WIDEBAND METAMATERIAL ANTENNA
Researcher : BASHIR D BALA (PHD-GRADUATED 2013)
There has been increasing interest in Metamaterials in the past 10 years in the scientific communities. However, metamaterials are sometimes regarded as left-Handed materials (LHM) or negative index materials by a lot of people including researchers. Since the concept of artificial LHM were proposed and experimentally realised researchers tried various ways to bring these special material with unusual electromagnetic properties into practical application. At microwave frequencies, some of the potential applications of LHM’s include substrate materials for antenna and microwave components, absorbing materials for engineering and radar applications, high impedance surfaces and Artificial Magnetic Conductors (AMC) and Tunable materials among others. In this research work, LHM will be studied for antenna application with the aim of achieving a wider bandwidth. Currently metameterials based on resonant approach suffers from narrow bandwidth and high material loss. This is attributed to the dependence of the resonance frequency of the DNG structures on its size. To achieve wideband metamaterial antenna, transmission line or non-resonant approach will employed with the aim of merging resonant modes together- the negative order, zero order and positive order modes. Different types of metamaterial antenna will be realised for specific applications such as multi-band, wideband and frequency reconfigurable antennas. Computer Simulation Technology (CST) microwave studio will be employed as the simulation tool and measurement of the result will be obtain via Vector network analyser (VNA) and Anechoic Chamber. The preliminary results obtain is promising when a Slab of DNG structure used as superstrate on a patch antenna improves its bandwidth at 2.4GHz. Also metamaterial antenna using triangular resonator was design for wide band application with the novelty of having only the resonator as the main radiating element.
RESEARCH TITLE: TEXTILE ARTFICIAL MAGNETIC CONDUCTOR WAVEGUIDE SHEET FOR TRANSMISSION ENHANCEMENT BETWEEN ANTENNAS FOR BODY CENTRIC COMMUNICATION
Researcher: KAMILIA KAMARDIN (PhD- GRADUATED 2014)
The rising interest in body centric communication is due to the need of a more reliable short-range wireless communication within a human body. Wireless Body Area Network (WBAN) associates with wearable devices that offers networking within human body which allows new conveniences and services. However, wearable antennas suffer performance degradation due to the distinct properties of human body itself. Radiation characteristics and input impedance of wearable antennas will be distorted when placed on human body. In addition, the radiation that goes towards human body is a major health concern. The presence of human body also introduces high transmission loss between on-body antennas. Good transmission between antennas are crucial for an efficient wireless networking system within human body. High transmission loss can lead to a non-reliable system that is undesired. This study proposes an artificial magnetic conductor (AMC) waveguide sheet that improves wireless on-body transmission. The sheet-like waveguide provides an independent transmission path which can reduce all distortions caused by human body. The proposed AMC waveguide sheet consists of textile substrate with radiating patches and ground plane made of conductive fabric. The flexibility of textile material make it suitable for wearable communications. The transmission characteristics between antennas was studied rigorously in this work. Compared to S21 transmission for antennas in free space, above metal plate, above dielectrics and on human body, the transmission between two antennas are greatly improved with the presence of AMC sheet. Transmission loss between the antennas have been significantly reduced apart from minimizing the radiation towards human body. In addition, body centric measurements were also investigated which includes bending, wetness, presence of human body and SAR. Different orientation and placement of the antennas were considered. The textile-based AMC waveguide sheet will act as a new approach for an efficient wearable wireless body-centric communications.
RESEARCH TITLE : MIMO CHANNEL CHARACTERIZATION WITH POLARIZATION DIVERSITY
Researcher: MOHD ZOINOL ABIDIN ABD AZIZ (PhD - GRADUATED 2015)
In recent years, the remarkable growth of wireless communication systems mainly in data transmission such as huge files, video and voice has increased the demand of higher data transfer rate. Thus, lead to the demand of higher channel capacity. MIMO (multiple input multiple output) systems which allow multiple parallel channel to be transmitted or received simultaneously is considered a breakthrough in solving the problem. In MIMO, the channel capacity is increased without additional transmit power or bandwidth. Furthermore, the technique called diversity has been proven to increase the channel capacity in MIMO systems. This project focus on the development of front end 4 X 4 wireless MIMO systems at 2.4GHz. The double stage diversity which combined polarization diversity and spatial diversity have been employed. X-polarized antenna with single port technique has been design to produce X linear polarization wave at 2.4GHz frequency. The design simulation and fabrication was done by using CST software and chemical etching technique. The configuration of typical, spatial diversity and polarization diversity has been set up and measured in indoor environment. Channel capacity for spatial and polarization diversity has improved up to 14.4% and 27.9% respectively. Meanwhile, X-polarized (double stage diversity) channel capacity has improved up to 17.75%.
RESEARCH TITLE: DESIGN AND DEVELOPMENT OF METAMATERIAL ABSORBER AT X BAND FREQUENCY
Researcher: OSMAN BIN AYOP (PhD - GRADUATED 2016)
This research proposes the design of microwave absorber based on metamaterial structure working at X-band frequency range. New structures of metamaterial are proposed to work at narrow band, multi-band, and wideband operating frequency. The research involves the critical analysis of each structures based on their reflectance, transmittance and absorbing performance from the interaction of incident electromagnetic waves with the designed structures. A perfect metamaterial absorber is obtained if the reflectance and transmittance values go to zero indicate that the structure is efficiently attenuates the incident electromagnetic waves through the structure. The absorbance value is then lead up to the maximum value (1) indicates that the 100% absorbance is achieved. These results obtained under a condition that the designed structures have the same surface impedance as the free space impedance during resonance. To achieve this impedance value, the complex frequency dependent effective permittivity and the effective permeability of the structure are the same value. In addition, the imaginary part of refractive index of the structures must be as high as possible to maximize the absorption. In the end of the research, new structures of metamaterial absorber will be designed, simulated, fabricated, measured and analysed for X-band frequency.
RESEARCH TITLE: RECONFIGURABLE ANTENNA WITH POLARIZATION AND PATTERN DIVERSITIES FOR LIMITED SPACE MIMO SYSTEMS
Researcher : MUHAMAD NASRUN OSMAN (PHD - GRADUATED 2016)
Wireless communication undergoes a dramatically change in recent years. More and more people are using modern communication services, thus increasing the need for more capacity in transmission. Since bandwidth is limited resources, and there is a limitation in term of high degree in modulation and power transmitted, the strongly increased demand in high transmission capacity has to be satisfied by a better use of existing frequency bands and channel conditions. One of the recent technical breakthroughs, which will be able to provide the necessary data rates and to meet the demands by the users, is the use of multiple antennas at both link ends known as Multiple-Input-Multiple-Output (MIMO) system. MIMO systems are capable of realizing higher throughput without increasing bandwidth or radiating power. In traditional MIMO normally adopted space separated antenna. Two famous techniques used in MIMO for space separated are spatial multiplexing and transmit/receive diversity. To employ these techniques required enough and extra space. However, for the limited-spaced applications like mobile terminals or portable access points, where there is no space available, these techniques are no longer an advantage. Due to this limitations, reconfigurable antenna has been found out can enhance the performance of the systems without required extra space, hence space resources can be saved and utilized. Reconfigurable antenna with radiation pattern only or polarization only has been examined can increase some percentages of capacity with compare to none reconfigure antenna. Thus, by exploit both radiation pattern and polarization diversity, it was great potential to increase the channel capacity offered by the MIMO systems.