Whyte, Griogair W.M. (2008) Antennas for wireless sensor network applications. PhD thesis, University of Glasgow.
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Abstract
The objective of this thesis is to present an analysis of antennas, which are applicable to wireless sensor networks and, in particular, to the requirements of the Speckled Computing Network Consortium. This was done through a review of the scientific literature on the subject, and the design, computer simulation, and experimental verification, of various suitable designs of antenna The first part of this thesis outlines what an antenna is and how it radiates. An insight is also given to the fundamental limitations of antennas. As antennas investigated in this thesis are planar-printed designs, an insight into the types of feed lines applicable, such as microstrip, CPW and slotline, is given. To help characterise the antennas investigated, the fundamental antenna analysis parameters, such as impedance bandwidth, S-parameters, radiation pattern, directivity, antenna efficiency, gain and polarisation are discussed. Also discussed is the 3D electromagnetic simulation software, HFSS, which was used to simulate the antennas in this thesis. To help illustrate the use of HFSS, a proximity-coupled patch antenna, operating at 5.8 GHz, was used as an example. A range of antennas were designed, manufactured and tested. These used conventional printed circuit boards (PCBs) and Gallium Arsenide (GaAs) substrates, operating at a range of frequencies from 2.4 GHz to 12 GHz. A review was conducted into relevant, suitable radio architectures such as, conventional narrowband systems, Ultra-Wide Band (UWB), and simplified radio architectures such as those based on the diode rectifier method, and Super Regenerative Receivers (SRR). There were several UWB antennas designed, which operate over a 3.1 – 10.16 GHz operational band with a VSWR ≤ 2. All the UWB antennas were required to transmit a UWB pulse with minimal distortion, which placed a requirement of linear phase and low values of group delay to minimise distortion on the pulse. UWB antennas investigated included a Vivaldi antenna, which was large, directional and gave excellent pulse transmission characteristics. A CPW-fed monopole was also investigated, which was small, omni-directional and had poor pulse transmission characteristics. A UWB dipole was designed for use in a UWB channel modelling experiment in collaboration with Strathclyde University. The initial UWB dipole investigated was a microstrip-fed structure that had unpredictable behaviour due to the feed, which excited leakage current down the feed cable and, as a result, distorted both the radiation pattern and the pulse. To minimise the leakage current, three other UWB dipoles were investigated. These were a CPW-fed UWB dipole with slots, a hybrid-feed UWB dipole, and a tapered-feed UWB dipole. Presented for these UWB dipoles are S-parameter results, obtained using a vector network analyser, and radiation pattern results obtained using an anechoic chamber. There were several antennas investigated in this thesis directly related to the Speckled Computing Consortiums objective of designing a 5mm3 ‘Speck’. These antennas were conventional narrowband antenna designs operating at either 2.45 GHz or 5.8 GHz. A Rectaxial antenna was designed at 2.45 GHz, which had excellent matching (S11 = -20dB) at the frequency of operation, and an omni-directional radiation pattern with a maximum gain of 2.69 dBi as measured in a far-field anechoic chamber. Attempts were made to increase the frequency of operation but this proved unsuccessful. Also investigated were antennas that were designed to be integrated with a 5.8 GHz MMIC transceiver. The first antenna investigated was a compact-folded dipole, which provided an insight into miniaturisation of antennas and the effect on antenna efficiency. The second antenna investigated was a ‘patch’ antenna. The ‘patch’ antenna utilised the entire geometry of the transceiver as a radiation mechanism and, as a result, had a much improved gain compared to the compact-folded dipole antenna. As the entire transceiver was an antenna, an investigation was carried into the amount of power flow through the transceiver with respect to the input power.
