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Modelling Small Transmitting Loops

Altair Forum User

I have successfully modelled several types of antennas in FEKO, but am having trouble modelling Small Transmitting Loops (aka magnetic loops). I'm using a faraday feed, small loop within the exterior loop (the exterior loop being less than 10% of the operating wavelength). I've followed the design principles of using a faraday loop that is 20% of the exterior loop. I include a capacitive load on the exterior loop. I've obtained empirical data on existing loops, but none of my models come even close to the measured values. Does anyone know of any tutorial material on modelling STLs in FEKO or have any suggestions?

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Mel

Hi Paul

Can you provide a model or at least a screen shot. It's way too difficult to comment otherwise.

Altair Forum User

Mel,

Thank you for replying. Here is more in-depth description of an STL. An STL is a large coil with a capacitor added to bring the system into resonance. It is unlike a large resonant loop in that the loop size must be smaller than a 1/4 wavelength and does not resonate on its own. With most STLs the loop size is typically 1/10 of a wavelength or smaller. The loop is brought into resonance by attaching a capacitor to the loop. The loop is tuned by changing the value of the capacitor. I've included the CADFEKO basic model I'm using as an attachment (for accuracy purposes it is necessary to use double precision in the FEKO solver). According to design documents and some empirical test data I was able to obtain, this loop should resonate at 14 MHz. However, I cannot find a resonance point. Any assistance would be very much appreciated.

Unable to find an attachment - read this blog

Mel

Hi Paul

Some suggestions.

Widen your frequency range. Perhaps the resonance is just off.

The small loop comes very close to the larger loop. Wires will quite likely not accurately model the coupling as they can only model axial current. I would model the loops with cylinders meshed into triangles. You can path sweep a circle around a loop to create them.

You would need a much much smaller than 'Standard' mesh. I would use 'Custom'. Especially where they almost touch, there the mesh triangles need to be of the same size roughly as the separation distance between the loops.

Altair Forum User

Thank you for the suggestions. I decided to try using Octagons with cylinders as the sides. I took this approach since the literature I have read about STLs states that Octagons perform similar to circular loops. I also expanded the frequency range as you recommended and was able to locate a resonance point in the new design. This will allow me to experiment so that I can understand the interactions between the various parameters. I am confident now that I can eventually get to the point where I can model circular loops. Thank you very much for the advice.