RF transformers considered as transmission line devices

The lumped element circuit model for broad-band transformers has been in use for at least 50 years. It was developed for audio frequency transformers. Unfortunately, it ceases to give accurate results when the length of the windings becomes significant with respect to the signal wavelength. This is the case in RF broad-band transformers. For these, a model based on transmission lines is proposed. This model will help the designer to visualise how the device works, enable him to set achievable design goals, and allow him to perform more accurate computer simulations of his RF circuits.