Unequal-split Wilkinsons

Revised December 5, 2004

Click here to go to our general discussion of Wilkinson power splitters.

We are talking about 2-way Wilkinson splitters here. The way to make power split unequally requires two things: the quarterwave sections must be of different impedance, to encourage more of the signal to travel in/out the lower-impedance arm, and a second set of quarter-wave sections are needed, to transform the arm impedances back to 50 ohms. The structure looks similar to a two-stage Wilkinson without the second isolation resistor (here "R_W" is the Wilkinson isolation resistor).

The following set of equations when satisfied ensure that the ports will be matched and port 2 and port 3 will be isolated (equation for Z_0A was corrected January 16, 2004):

Plotted below are the four line impedances and the isolation resistor value as functions of the power split express in dB.

Below are plots of the power split and impedance match for PA/PB=4.0. The insertion loss bandwidth is reduced compared to the equal-split Wilkinson, but the isolation bandwidth is nearly the same. We didn't bother to plot the isolation.