This dissertation presents the investigation of antennas with improved performances at microwave frequencies. It covers the following three topics: the study of the metamaterial with near-zero index of refraction and its application in directive antenna design, the design technique of a wideband circularly polarized patch antenna for 60GHz wireless application and the investigation of a novel direction of arrival (DOA) estimation technique inspired by human auditory system. First, the metamaterial composed of two-dimensional (2-D) metallic wire arrays is investigated as an effective medium with an effective index of refraction less than unity (n(eff) < 1). The effective medium parameters (permittivity ε(eff), permeability μ(eff) and n(eff)) of a wire array are extracted from the finite-element simulated scattering parameters and verified through a 2-D electromagnetic band gap (EBG) structure case study. A simple design methodology for directive monopole antennas is introduced by embedding a monopole within a metallic wire array with n(eff) < 1 at the antenna operating frequencies. The narrow beam effect of the monopole antenna is demonstrated in both simulation and experiment at X-band (8 – 12 GHz). The measured antenna properties including return loss and radiation patterns are in good agreement with simulation results. Parametric studies of the antenna system are performed. The physical principles and interpretations of the directive monopole antenna embedded in the wire array medium are also discussed. Second, a fully packaged wideband circularly polarized patch antenna is designed for 60GHz wireless communication. The patch antenna incorporates a diagonal slot at the center and features a superstrate and an air cavity backing to achieve desired performances including wide bandwidth, high efficiency and low axial ratio. The detailed design procedure of the circularly polarized antenna, including the design of the microstrip-fed patch antenna and the comparison of the performances of the antenna with different feeding interfaces, is described. The experimental results of the final packaged antenna agree reasonably with the simulation results. Third, an improved two-antenna direction of arrival (DOA) estimation technique is explored, which is inspired by the human auditory system. The idea of this work is to utilize a lossy scatter, which emulates the low-pass filtering function of the human head at high frequency, to achieve more accurate DOA estimation. A simple 2-monopole example is studied and the multiple signal classification (MUSIC) algorithm is applied to calculate the DOA. The improved estimation accuracy is demonstrated in both simulation and experiment. Furthermore, inspired by the sound localization capability of human using just a single ear, a novel direction of arrival estimation technique using a single UWB antenna is proposed and studied. The DOA estimation accuracies of the single UWB antenna are studied in the x-y, x-z and y-z planes with different Signal to Noise Ratios (SNR). The proposed single antenna DOA technique is demonstrated in both simulation and experiment, although with reduced accuracy comparing with the case of two antennas with a scatter in between. At the end, the conclusions of this dissertation are drawn and possible future works are discussed.

The thesis deals with the design and implementation of broadband and narrowband antennas and their applications in practical environment. In this thesis, a new concept for designing the UWB antenna is proposed based on the CRLH metamaterials and this UWB antenna covers a frequency range from 2.45 GHz to 11.6 GHz. Based on the design of the UWB antenna, another antenna is developed that can cover a very wide bandwidth i.e from 0.66 GHz to 120 GHz. This antenna can not only be used for UWB applications but also for other communication systems working below the UWB spectrum such as GSM, GPS, PCS and Bluetooth. The proposed antenna covering the bandwidth from 0.66 GHz to 120 GHz is by far the largest bandwidth antenna developed based on metamaterials. Wide band antennas are not preferred for sensing purpose as it is difficult to differentiate the received signals. A multiband antenna which can be used as a strain sensor for structural health monitoring is proposed. The idea is to correlate the strain applied along the length or width with the multiple resonant frequencies. This gives the advantage of detecting the strain applied along any direction (either length or width), thus increasing the sensing accuracy. Design and application of a narrow-band antenna as a temperature sensor is also presented. This sensor can be used to detect very high temperature changes (>10000C). This sensor does not require a battery, can be probed wirelessly, simple and can be easily fabricated, can withstand harsh environmental conditions.

No description available.

A direction of arrival (DoA) estimation technique for broadband microwave signals is proposed using a single ultrawideband antenna. It is inspired by the sound source localization ability of a human auditory system using just one ear (monaural localization). By exploiting the incident angle-dependent frequency response of a wideband antenna, the DoA of a broadband microwave signal can be estimated. The DoA estimation accuracies are evaluated for two antenna configurations and microwave signals with different signal-to-noise ratios. Encouraging the DoA estimation performance of the proposed technique is demonstrated in both simulation and experiment.

No / A miniaturized modified planar inverted-F antenna (PIFA) is presented and experimentally studied. This antenna consists of a planar rectangular monopole top-loaded with a rectangular patch attached to two rectangular plates, one shorted to the ground and the other suspended, both placed at the optimum distance on each side of the planar monopole. The fabricated antenna prototype had a measured impedance bandwidth of 125%, covering 3 to 13GHz for reflection coefficient better than -10 dB. The radiator size was 20 x 10 x 7.5 mm(3), making it electrically small over most of the band and suitable for incorporation in mobile devices. The radiation patterns and gains of this antenna have been cross-validated numerically and experimentally and confirm that this antenna has adequate characteristics for short range ultra-wideband wireless applications.

Yes / An efficient multi-object evolutionary algorithms are proposed for optimizing frequency characteristics of antennas based on an interfacing created by Matlab environment. This interface makes a link with CST Microwave studio where the electromagnetic investigation of antenna is realized. Very small, compact printed monopole antenna is optimized for ultra- wideband (UWB) applications. Two objective functions are introduced; the first function intends to increase the impedance bandwidth, and second function to tune the antenna to resonate at a particular frequency. The two functions operate in the range of 3.2 to 10.6 GHz and depend on the level of return loss. The computed results provide a set of proper design for UWB system in which the bandwidth achieved is 7.5GHz at the resonance frequency 4.48GHz, including relatively stable gain and radiation patterns across the operating band.

Yes / A novel dual-polarized patch antenna for ultra-wideband (UWB) applications is presented. The antenna consists of a square patch and four capacitively coupled feeds to enhance the impedance bandwidth. Each feed is formed by a vertical isosceles trapezoidal patch and a horizontal isosceles triangular patch. The four feeds are connected to the microstrip lines that are printed on the bottom layer of the grounded FR4 substrate. Two tapered baluns are utilized to excite the antenna to achieve high isolation between the ports and reduce the cross-polarization levels. In order to increase the antenna gain and reduce the backward radiation, a compact surface mounted cavity is integrated with the antenna. The antenna prototype has achieved an impedance bandwidth of 112% at (|S11| ≤ -10 dB) whereas the coupling between the two ports is below -28 dB across the operating frequency range. The measured antenna gain varies from 3.91 to 10.2 dBi for port 1 and from 3.38 to 9.21 dBi for port 2, with a 3-dB gain bandwidth of 107%. / IEEE Antennas and Propagation Society

No / To mitigate potential interferences with coexisting wireless systems operating over 3.3-3.6 GHz, 5.15-5.35 GHz, or 5.725-5.825 GHz bands, four novel band-notched antennas suitable for ultra-wideband (UWB) applications are proposed. These include UWB antennas with a single wide notched band, a single narrow notched band, dual notched bands, and triple notched bands. Each antenna comprises a half-circle shaped patch with an open rectangular slot and a half-circle shaped ground plane. Good band-notched performance is achieved by using high permittivity and low dielectric loss substrate, and inserting quarter-wavelength horizontal/vertical stubs or alternatively embedding quarter-wavelength open-ended slots within the feed line. The results of both simulation and measurement confirm that the gain suppression of the single and multiple band-notched antennas in each desired notched band are over 15 dB and 10 dB, respectively. The radiation pattern of the proposed triple band-notched design is relatively stable across the operating frequency band.

No / A compact-size asymmetrical linearly tapered slot antenna required for portable ultra-wideband (UWB) imaging systems is presented. The total antenna size is reduced compared with the conventional linearly tapered slot antenna by using a triangular slot on the left-hand side of the tapered-shaped radiator, whereas introducing a corrugated pattern of cuts on the right side. The antenna operates over a wide bandwidth extending from 3.1 to 10.6 GHz with a maximum gain of 8.5 dBi. Stable radiation patterns are observed across the operational bandwidth, with cross-polarization levels below 20 dB. The realized antenna structure occupies a volume of 35 x 36 x 0.8 mm3, and possesses the essential time domain fidelity needed for UWB imaging applications. (c) 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Libyan Ministry of Higher Education. / The full text will be available at the end of the embargo: 28th Nov 2024 / Subtitle: Simulation and Measurement of Reconfigurable Antennas for Cognitive Radio, UWB Applications, Investigation of Antenna Gain and Efficiency, Frequency Tuneable Range, Antenna Radiation Performance and Antenna Design Optimization using Parametric Studies as well as using MIMO antenna for wireless body area networks