You can experiment with wideband magnetic loop design with the LTSpice Magnetic Loop Model. Download here.
This fall, I have spent a lot of time studying antenna theory and developing an understanding of how and why wideband magnetic loop antennas work. Whew. I learned a lot and have written some articles describing theory and practice.
Early on, I discovered a great article from Lionel Loudet describing loop theory and containing an LTSpice Magnetic Loop Model. Unfortunately, there were two challenges with this model. First, it was only partially documented, with no details on how radiation resistance or AC loss resistance were calculated. Second, there was no download. So, I decided to reproduce the Loudet model and add in the missing details as best as I could figure them out.
Here is the result of my efforts, a complete equivalent circuit model for a magnetic loop antenna. What’s more, I am making the model available for you to download and use.
You can read complete documentation for all the formulas used. Just extract the files into a separate folder for use with LTSpice. The circuit is quite complex, but you should be able to understand everything I did and why.
LTSpice Magnetic Loop Model – How to Use It
So, how can you use this model, and why? Three things.
First, you will be able to follow the Loudet model from his article, and experiment with different antenna voltages and currents. Second, this model gives you a good on-ramp for using LTSpice in your circuit designs, if you have not already started down this path. LTSpice is free and not that hard to learn if you have a basic electronics understanding.
Third, and most important, you can now use LTSpice for evaluating different amplifiers and system designs. So far, I have tried the model with a variety of published amplifiers and loop articles. More on these experiments later.
To get started, just use the Test Jig included with the WML_C files. This model is designed as a Hierarchical Bloc that you can just insert into your LTSpice model. Three parameters are available for you to adjust. Two are physical – loop and wire diameter for a single turn aluminum loop. The third parameter is the strength of the radio signal in volts per meter.