The Kootwijk VLF Antenna: A Numerical Model
A comprehensive analysis of the historical Kootwijk VLF (Very Low Frequency, which covers 3-30 kHz) antenna, including the development of a numerical model to gain insight into its operation.
The Kootwijk VLF antenna played a significant role in long-range communication during the early 20th century. The paper addresses the challenge of accurately modelling this electrically small antenna due to limited historical technical information and its complex design.
The main goal is to understand if the antenna’s radiation efficiency might explain why “results were disappointing” for the Kootwijk to Malabar (Indonesia) communications link.
Through simulations and comparisons with historical records, the numerical model reveals that the Kootwijk VLF antenna had a low radiation efficiency – about 8.9% – for such a long-distance link.
This work discusses additional loss mechanisms in the antenna system that might not have been considered previously, including increased transmission-line losses as a result of impedance mismatch, wires having a lower effective conductivity than copper and inductor quality factors being lower than expected.
The study provides insights into key antenna parameters, such as the radiation pattern, the antenna’s quality factor, half-power bandwidth and effective height, as well as the radiated power level and the power lost through dissipation.
This research presents the first documented numerical analysis of the Kootwijk VLF antenna and contributes to a better understanding of its historical performance.
While the focus has been at VLF, this work can aid future modelling efforts for electrically small antennas at other frequency bands.
M. C. Walden, “The Kootwijk VLF Antenna: A Numerical Model”, 18th European Conference on Antennas and Propagation, EuCAP 2024, Glasgow, UK, 17–22 March 2024.
doi: 10.23919/EuCAP60739.2024.10501016
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