Hashmi, Muhammad Abdur Rehman; (2023) Antenna design and optimisation for UHF glacial environmental sensor networks. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Our planet’s ice masses play an important role in regulating numerous natural phenomena vital to keep our planet habitable by humans as well as other living species. Since few decades, global climate changes are probably responsible for an increased melt rate of the ice masses causing catastrophes. It is therefore desirable to monitor our planet’s ice masses for predicting catastrophes and timely initiating disaster management measures. This monitoring can also provide scientific evidence for supporting anti-climate change efforts. This research contributes to a joint UCL (University College London) – BAS (British Antarctic Survey) project that aims to develop and deploy an Environmental Sensor Network (ESN) at the Thwaites glacier, Antarctica. Glacial ESNs reported in the last two decades are reviewed, focusing on the antenna types used. A link budget framework for designing such antenna systems is presented. As an example, the framework has been used to design an antenna system for deployment at the Thwaites glacier, Antarctica. Design details of six circularly polarized (CP) antennas, one for the englacial sensor probes and five for supraglacial surface receivers are presented. The probe antenna is a 3D bent cross dipole that fits within a borehole of 8 cm diameter while providing a 1 dBic gain at 433 MHz in ice. The other five antennas are printed ones made for use with glacier surface receivers to receive information transmitted by the englacial sensor probes. Out of five, three are cross dipole antennas, while the remaining two are of Archimedean spiral type. All these six antennas provide 3 dB beamwidths of at least 50º in the xz and yz vertical planes catering for transmitter-receiver antenna misalignments caused by extended deployments. The printed cross dipole versions 1 and 2, and the half ring shaped cross dipole antennas for surface receivers provide realized gains of 6.1 dBic, 5.9 dBic, and 5.9 dBic respectively with a quarter wave reflector. The version 2 antenna provides size reduction at the cost of minor gain loss compared to the version 1 antenna. The half ring cross dipole antenna provides improvements in terms of a lower profile, wider 3 dB beamwidth, smaller axial ratio, and purer polarization over all the other antennas developed for use with surface receivers. The axial ratios of all four cross dipole antennas remained below 1.1 dB within the 330-580 MHz band while the co-polarizations remained adequately stronger than the cross polarizations within a 40º beamwidth in both the vertical planes. The spiral antenna version 1 provides a gain of 7.4 dBic at 433 MHz and a -10 dB fractional bandwidth of 47% in snow. Through some design modifications, the version 2 spiral antenna provides significant improvements in the antenna’s reflection coefficient, gain, total efficiency, and axial ratio over the version 1 spiral antenna. None of the previous works used these antenna types for the said applications. The previous works used helical, coil ferrite, and Dielectric Resonator antennas for the sensor probe. Types of antennas previously used with surface receivers included Yagi, helical, non-printed cross dipole, and log periodic dipole array. Lastly, the feasibility of 433 MHz band has been investigated for communication ranges up to 2300 metres through ice. Previous works used lower frequencies like 30 MHz, and 151 MHz to achieve such ranges.

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