Recent years have witnessed a growing demand for broadband wireless communication services such as on-the-go web-browsing, high speed data transfer and streaming of high definition multimedia. In response to this growth, there has been a rapid progress in research and development of technologies supporting high-speed wireless networks offering flexibility and scalability to heterogeneous consumer requirements. A fundamental challenge to the reliable operation of a wireless communication link is the wireless channel which is influenced by time-variant noise, interference, multipath and scarcity of the available frequency spectrum. Due to the wireless nature of the signal transmission and the manner in which energy is distributed or collected, an antenna has a profound influence on an efficient operation of wireless link. Because nowadays an antenna is required to work with many wireless standards, it poses one of the most difficult design and development technological problems. In the past, many antenna designs were concentrated on conventional outdoor applications such as satellite communications, terrestrial point to point communications and cellular base stations. In these applications, the primary design goal was the antenna electrical performance. In case of indoor applications, the designer has to pay attention not only to the electrical performance but also to mechanical, environmental and aesthetic features of antenna. In this thesis, the investigations into design and development of antenna for indoor wireless communication systems that are either currently widespread or quickly entering the consumer market are carried out. First, a single band circularly polarized Radial Line Slot Array antenna covering 2.4GHz ISM frequency spectrum of IEEE 802.11b/g protocol is proposed. Then, an access point antenna for IEEE 802.11a/b/g WLAN applications operating in a dual frequency band covering 2.4GHz and 5.2GHz frequency spectra is described. It consists of a RLSA antenna and a patch antenna combined in one body. During the design stage, in addition to characteristics such as return loss, radiation pattern and polarization, attention is paid to mechanical rigidity, light weight and low visual impact of these radiating structures. A low manufacturing cost is also part of the design strategy. This is important because of competitive commercial market of WLAN applications which is sensitive to the development cost. In theoretical investigations, a Field Matching Method is utilized to achieve a first order approximation to the coaxial-to-waveguide transition forming the feeding element of the RLSA antenna. Next, the full EM analysis (HFSS™) based on Field Element Method is applied to simulate the single and dual band antennas. Both types of access point antennas are manufactured and tested. Experimental results are compared with simulation results. The next part of this thesis presents the investigations into antenna diversity techniques for a wireless communication link in an indoor environment. The design of the automated experimental testbed is presented. This testing facility is used to measure the signal strength levels of a communication link between a mobile wireless device and an access point when they are equipped with multiple element antennas (MEAs). Special attention is given to the benefits of using MEA in a rich scattering environment that is accompanied the experiment. Full design details including electrical and mechanical features are provided. For a given feeding configuration, the testbed allows for measuring the received signal strength when the receiving module is moved over a circular area in an indoor environment. First set of experiments concerns the MEA system that utilizes two single-port transceivers each equipped with either 180º or 90º 3dB hybrid. By using alternatively one of the two input ports of the hybrids to feed a pair of monopole antennas several different transmission or reception modes of the 2x2 MEA communication link are investigated. The next set of experiments focuses on the performances of an indoor wireless system which uses either linearly or circularly polarized antennas at the two sides of the communication link. The overall diversity results indicate that by marginally increasing an overall system complexity (by using simple hybrid circuits and antennas), traditional transceiver systems equipped with MEA can provide significant improvements in the quality of indoor wireless link. The final part of this thesis presents the investigations into the design of planar monopole antennas that offer good return loss and omni-directional radiation pattern characteristics over an Ultra Wide frequency Band (UWB) spanning from 3.1GHz to 10.6GHz. Two types of planar monopole antennas are investigated. First, the ring type square with semi-circular base monopole antenna placed vertically above a finite ground plane is introduced followed by its design, manufacturing and testing. The second UWB antenna which is proposed in this thesis is a printed square with semi-circular base monopole antenna. This antenna is positioned in the same plane as ground and thus offers direct integration with a front-end circuitry of wireless transceiver. Several variations of this type of antenna featuring different outlines are designed, manufactured and tested. The obtained experimental results show a good agreement with the simulation results, as accomplished with the full EM analysis and simulation software HFSS™.
| Identifer | oai:union.ndltd.org:ADTP/286108 |
| Creators | Serguei Zagriatski |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
Page generated in 0.0026 seconds