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Transmission Line Transformer on Ferrite Core (Closed Form): XFERTL1



XFERTL1 is a behavioral model of a Guanella Balun transformer. This transformer consists of several Tx lines wound on ferrite core. Inputs of all lines are connected in parallel, and outputs are connected in series. This Tx line transformer provides highly efficient impedance matching within a relatively wide frequency bandpass.

Equivalent Circuit


Name Description Unit Type Default
ID Element ID Text XU#
Zo Char. imped of Tx line Resistance 50 ohm
Len Physical length of Tx line Length L1
Er Effective dielectric constant of Tx line   1
A Attenuation constant of Tx line (dB/m)   0
F Frequency for scaling of Tx line attenuation Frequency 0 GHz
N Number of turns of line around the ferrite core   1
AL Inductive index (inductance/turn)[1]) Inductance 1 nH
Order Number of Tx lines   1

[1] User-modifiable default. Modify by editing under $DEFAULT_VALUES in the default.lpf file in the root installation directory.

Implementation Details

XFERTL1 is comprised of several four-port two-conductor Tx lines. The number of lines is equal to Order. Inputs of all lines are connected in parallel, outputs are connected in series. Characteristic parameters of each line are specified via XFERTL1 parameters. Conductors of each Tx line have choke inductances Lc attached in parallel (see "Equivalent Circuit"). These inductances actually account for the presence of ferrite core. To define Lc, you must specify the number of turns (of Tx line winding on ferrite core) and inductance per turn. The resulting transformer provides transformation ratio N = Order2:1.

The choking inductance, Lc, is

The attenuation A(F) has the following frequency dependence:

where f is a simulation frequency.


This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.


[1] Jerry Sevick, Transmission Line Transformers, 4th Ed., SciTech Publishing, 2001.

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