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The Wilkinson power divider is a common three-port power divider circuit used to split an input signal into two equal output signals, or to combine two signals into one. Unlike resistive or T-junction power dividers, the Wilkinson power divider allows for almost complete isolation between the two ports and does not add resistive losses to the power division. Due to these properties, Wilkinson dividers are widely used in radio communication systems due to their ability to prevent crosstalk between channels (a phenomenon where one signal (or channel) affects the transmission of another signal (or channel)). Here, we will see how to model a Wilkinson divider using COMSOL Multiphysics and the RF Module.
Modeling a Wilkinson Power Divider
A Wilkinson power divider uses two microstrip lines mounted on a dielectric substrate to split an input signal into two equal outputs with a resistor mounted between the two output ports.
The geometry of the Wilkinson power divider model consists of a three-port device consisting of a 50 Ω microstrip line and a 70.7 Ω microstrip line, and a 100 Ω resistor between the ports. The relative dielectric constant, ε r, of the 60 mil substrate is 3.38. In addition, the geometry includes a metal frame that holds the voltage divider, four screws, and an SMA connector for each of the three ports.
These components can all be modeled using the Perfect Electric Conductor (PEC) boundary feature, while the 100 Ω resistor is modeled using a lumped element with an impedance of 100 Ω. The figure below shows the symmetrical electric field distribution at the top of the voltage divider, demonstrating how the input energy is coupled equally to both output ports.
The electric field norm shows that the input power is divided equally between the two output ports.
In the figure below, the S-parameters are plotted showing the frequency response of the voltage divider. At 3 GHz the input match is very good and the input power is divided equally between the two output ports, indicating that there are no resistive losses during power division. This figure shows the typical frequency response expected for all three-port Wilkinson power dividers.
The S-parameters show the frequency response curve of the crossover, indicating that the coupled power to each output port is approximately -3 dB at approximately 3 GHz.
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