Small but Tubby: A Magnetic Loop Antenna Made from 100 mm Copper Tubing
Abstract
This paper presents the electrical model, key equations, and practical construction of a small transmitting magnetic loop antenna built from unusually large 100 mm diameter copper tubing. The large conductor surface area and wide-area transitions to the vacuum capacitors were designed to minimize resistive losses. The frequency range from 1.8 MHz to 31 MHz is unusually wide. Frequency, impedance matching, and azimuth are all adjusted automatically by servo motors. Indoor losses originate predominantly from near-field coupling to the environment rather than from the antenna itself. Temperature-rise measurements confirm that the bulk of the dissipated power is absorbed by the environment, not by the antenna components. The conducted H-field measurements demonstrate good agreement between the measured H-field and the theoretical free-space H-field calculated from the antenna geometry and an estimated loop current. The loop current was estimated from the measured antenna bandwidth and the applied transmit power. The antenna was developed for indoor operation where outdoor installation is not possible.
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BibTeX
@misc{marki2026small,
title = {{Small but Tubby: A Magnetic Loop Antenna Made from 100 mm Copper Tubing}},
author = {Peter Märki and Markus Niese},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.10828},
eprint = {2607.10828},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.10828},
}
RIS
TY - UNPB
TI - Small but Tubby: A Magnetic Loop Antenna Made from 100 mm Copper Tubing
AU - Peter Märki
AU - Markus Niese
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2607.10828
UR - https://arxiv.org/abs/2607.10828
AB - This paper presents the electrical model, key equations, and practical construction of a small transmitting magnetic loop antenna built from unusually large 100 mm diameter copper tubing. The large conductor surface area and wide-area transitions to the vacuum capacitors were designed to minimize resistive losses. The frequency range from 1.8 MHz to 31 MHz is unusually wide. Frequency, impedance matching, and azimuth are all adjusted automatically by servo motors. Indoor losses originate predominantly from near-field coupling to the environment rather than from the antenna itself. Temperature-rise measurements confirm that the bulk of the dissipated power is absorbed by the environment, not by the antenna components. The conducted H-field measurements demonstrate good agreement between the measured H-field and the theoretical free-space H-field calculated from the antenna geometry and an estimated loop current. The loop current was estimated from the measured antenna bandwidth and the applied transmit power. The antenna was developed for indoor operation where outdoor installation is not possible.
ER -