Precision Simulations with AN-SOF for Magnetic Loop Antennas

Magnetic loop antennas are widely used in amateur radio. A common design involves a dual-loop configuration where a larger loop, equipped with a tuning capacitor, is magnetically coupled to a smaller, internal loop. The coaxial cable feeding the antenna connects to the smaller loop. This antenna is simple to construct using readily available coaxial cable. Importantly, the interaction between the loops is inductive, not physical.

The accompanying figure shows a simulation of a magnetic loop antenna. The larger loop, made from RG-8 cable, has a diameter of 70 cm, while the smaller loop, made from RG-6 cable, has a diameter of 15 cm. The loops are separated by 2 cm at the base. The required tuning capacitor values for resonance at 3.5, 7, 14, 21, and 29 MHz are indicated.

Placed one meter above a ground plane, the antenna’s radiation pattern deviates from the typical toroidal shape expected of a small loop in free space. The color scale on the loops represents current distribution at each resonant frequency.

The AN-SOF Antenna Simulator enables accurate simulations of this antenna design using the Conformal Method of Moments with curved segments to precisely model loop shapes. AN-SOF’s exact Kernel accurately handles the close proximity of the loops at the antenna’s base.

The simulator streamlines the calculation process by automating resonance calculations for the five specified frequencies. To access this feature, go to the AN-SOF main menu and select “Run Bulk Simulation” under the “Run” category. This allows you to easily run calculations on the five provided .nec files, which can be downloaded by pressing the “Download Model” button above. Importantly, this feature is available in the trial version of AN-SOF.