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Precision Simulations with AN-SOF for Magnetic Loop Antennas

Magnetic loop antennas find extensive application within the realm of amateur radio pursuits. One prevalent design employs a dual loop configuration, wherein a larger loop, equipped with a tuning capacitor at one end, is magnetically linked to a smaller loop positioned inside it. The smaller loop serves as the connection point for the coaxial cable, which feeds the antenna. This antenna’s construction is remarkably straightforward, as it capitalizes on the adaptability of coaxial cable wires for assembly. It is important to emphasize that the interplay between the two loops is rooted in induction rather than physical linkage.

Illustrated in the accompanying image, the simulation delves into an instance where the larger loop, fashioned from RG-8 cable, spans a diameter of 70 cm, while the smaller loop, crafted from RG-6 cable, boasts a 15 cm diameter. Maintaining a separation of 2 cm between the loops at the antenna’s base, the provided diagram outlines the requisite tuning capacitor settings for achieving resonance across five distinct frequencies: 3.5, 7, 14, 21, and 29 MHz.

Sequence of images depicting radiation pattern, current distribution, and tuning capacitor values for magnetic loop antenna at 5 resonant frequencies.
A series of images showcasing radiation patterns, current distributions, and tuning capacitor values for the magnetic loop antenna across 3.5, 7, 14, 21, and 29 MHz. Simulated using AN-SOF Antenna Simulator.

Sited a meter above a typical ground plane, the antenna showcases a radiation pattern that diverges from the conventional toroidal shape anticipated for a small loop positioned in free space. The color scale displayed on the loops indicates the current intensity corresponding to each resonant frequency.

Facilitating precise simulations of this antenna design, the AN-SOF Antenna Simulator leverages the Conformal Method of Moments featuring curved segments. This enables the meticulous replication of loop contours. A noteworthy attribute of AN-SOF lies in its use of an exact Kernel, which accommodates close proximity of both loops at the antenna’s base.

The simulator further streamlines the calculation process by permitting sequential and automated execution of the antenna’s resonance calculations across the five specified frequencies. This eliminates the need for manual execution of each calculation. To access this feature, navigate to the AN-SOF main menu and select Run Bulk Simulation under the “Run” category. This function allows you to effortlessly run calculations on the five “.nec” files, available for download via the provided button. Importantly, this functionality is available even with the trial version of AN-SOF.

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